Simple Guide, How to add Additive to Gearbox C4 II, B7, 2013, Citroen

[frer8833]

Guide on how to top up with gearbox oil additive.

This very simple DIY method may be applicable to similar models.

Overall effect from using oil additive in both engine and gearbox: smoother acceleration with more power and car sounds more lubricated.

I added 6% of an oil additive called Mecarun P18 to the gearbox (an EGS6 but it works for manual too) because it is a car with old, but lifetime, gearbox oil.

Mecarun states that 6% is for harder driving conditions so I emptied a second bottle into the engine oil reservoir. In older cars 6% is better because they accumulate stress and wear from real world driving, the effect is also more noticeable for the driver in terms of sound, engine smoothness, fuel economy.

Oil additives like Mecarun P18 and Mannol can reduce friction over 20%. Even adding just 1% ester based friction modifier to 4L of 5w20 engine oil reduced the friction by 12.45% and improved fuel economy by 2.33%¹. Mecarun P18 may give 5-10% better fuel economy according to a reseller². In comparison using 5w20 engine oil instead of 5w30 reduces friction 1-2% but with risk of insufficient lubrication.

There are similar additives like Mannol 9829, 9929, 9903, and 9091 that form a resilient oil film on metal parts but that is different than Mecarun P18 which creates a sub-micron thick, super slippery, and permanent metal coating which is much better. 6% Mecarun P18 + 3% Mannol additive may be even better as it can improve the old gearbox oil (but try not to overfill the gearbox, max is 2.2-2.3L).

How I poured additive into gearbox (pics):

First I detached the lower end of the air intake pipe to make more room for my hand. Then I inserted my hand, palm up, into the area where the gearbox oil refill lid is located and turned my palm down, pulled off the lid and turned palm up again with lid between my fingers and pulled my hand out. A plastic bag covered my arm against scratches with holes for my fingers. The pump nozzle was shortened to improve the flow of the thick fluid.

The gearbox oil specification is PSA Peugeot/Citroën B71 2330. 2.1L +/- 0.1L refill after draining (semiauto/manual). B71 is C4 II.

BTW, on this C4 B7 model I prefer 205/60R16 tyres for better cushioning compared with OEM size 205/55R16.

¹"Experimental Research on the Impact of Lubricating Oils on Engine
Friction and Vehicle Fuel Economy" https://www.atlantis-press.com/article/25837920.pdf
²"This improvement in engine performance contributes in particular to a significant reduction in fuel consumption. For driving primarily in cities, the savings achieved are estimated at 5 to 10% depending on the vehicle." https://additifs-auto.com/hyper-lubrifi ... oteur.html

[akerolf]

Can you specify little further how to locate the fill plug for gearbox oil? My car is C4 2011 automat.

[frer8833]

Hi akerolf.

The filler plug is almost directly below the black battery tray. In the picture, you can follow the transparent PVC hose (next to the syringe with red additive fluid) back to the oil filler cap/lid. You’ll need a flashlight to see the lid clearly.

Without checking your VIN number you either have the semiauto version with small knob actuator handle in the center console (automated manual transmission) with gear shifting paddles behind steering wheel or the manual version with regular "big" gear shifter and no paddles.

If it is a C4 II (B7), then the gear oil spec is B71 2330, which is same for both semiauto and manual. There should still be 2.1 litres in the gearbox since car left factory because gearboxes have low temperature and don't consume oil unlike car engines. If the gearbox oil level is low because of leakage, you'd get a low gearbox oil error code in the OBD2 scanner. So I assume your car still has 2.1L in the gearbox.

There is no dipstick to check gearbox oil level. If you drain the gearbox you can see how much it is by collecting it in a measuring bottle or weigh it on a scale and pour back in an equal amount through the top refill (venting mount) hole. If you overfill a little bit, you may be able to use a syringe and hose to suck the surplus back out through the same top refill hole.

Do you have a problem with your gearbox, any symptoms? If not, I recommend simply topping up with 125ml of gearbox oil additive. This is more convenient than draining and refilling.

You can write a clear note in the vehicle’s service book or maintenance log stating the date, mileage, exact amount (125ml), and product name of gearbox oil additive. This helps prevent accidental overfilling by future owners or mechanics.

(BTW older cars are susceptible to rust, so when car is dry I inspect the vehicle from all angles, including underneath. On rusty areas I first spray brake cleaner, wipe clean with a cloth, and then apply 2–3 coats of 1K touch-up paint from spray can, using the car’s color code, and finish with 1-2 coats of 1K clear varnish from spray can. This saves the car from becoming destroyed by rust.)

[akerolf]

Hi frer8833,

Tanx for your replay!

[frer8833]

You're welcome, akerolf!

After adding the leftover fluid in the additive bottle, the engine now contains 9% Mecarun P18, up from 6%, which is a clear improvement in how the engine feels (more efficiency, more fuel saving). The gearbox still has its 6%.

Mecarun recommends 8% in both engine and gearbox, for most extreme driving. In tests it increased torque/hp, lowered drivetrain temperature and noise, resulted in metal to metal 85% friction reduction*.

Mecarun P18 contains antioxidants which can extend the life of the engine/gearbox oil if it is added at the oil change.

A good cheaper alternative is Mannol 9929, 10% in engine and 6% in gearbox (or extract/drain a little gearbox oil first to ensure not overfilling and add 10%).

My simple method avoids this complicated drain and refill disassembly shown in this YouTube video, which states 1.9L but should be at least 2L.



*"Épreuves d'endurance ou conditions extrêmes : jusqu'à 8% du volume d'huile", "Boîtes séquentielles à usage intensif : jusqu'à 8%", "Augmenter le dosage à 7-8% for rallye and tout-terrain for conditions extrêmes (poussière, variations de température)" and "Réduction de friction Jusqu'à 85% selon tests tribologiques spécifiques". Auto Detailing Reims,
https://web.archive.org/web/20250425120 ... itesses-1l

[frer8833]

Update: A mechanic drained the old gearbox oil and refilled it with fresh oil. The gearbox now feels smoother and quieter than it did with the old oil plus an additive.

Mileage was 270,000 km, so that “lifetime fluid” was probably a bit overdue

It can still feel a bit jerky sometimes when creeping in 1st gear, but that seems more related to clutch behaviour than the oil. It might be improved with a clutch bite point relearn/readaptation.

I haven’t tried adding an additive like Mecarun P18 to the new oil yet, but it might improve things even further.

If you change the gearbox oil every 5 years, you probably don’t need an additive. But if you only change it every 10 years, and especially if you do a lot of high speed motorway driving, frequent mountain driving, regular towing, long runs with heavy loads, or if the engine has been tuned for higher torque, an additive might be worth considering.

[frer8833]

To correct several critical misconceptions regarding the EGS6 (MCM/BVMP6) transmission, and to rectify some of my own earlier comments, here is the definitive breakdown of PSA product descriptions, fluid volumes, and additive chemistry for vehicles like the Citroën C4 B7 and Peugeot 3008:

Fluid Level Warning: First, it is a dangerous myth that a low mechanical gearbox oil level from a leak will trigger an OBD2 error code or dashboard symbol. The mechanical gearbox housing completely lacks an electronic level or pressure sensor; it can leak until bone-dry and self-destruct without warning. The warning symbols and error codes people experience related to "low fluid" actually stem exclusively from pressure loss in the completely separate electro-hydraulic actuator unit (which uses a distinct hydraulic fluid, such as Tutela CS Speed, not the gear oil).

Volume Specifications: Second, regarding oil capacity for the EGS6: The official factory specification dictates a refill volume of 2.1 liters (±0.1L) after a standard drain and refill, and 2.2 liters (±0.1L) following a complete overhaul. (Note: Newer ETG6 evolutions from 2013/2014 onward utilize a physically redesigned, smaller casing revised by PSA to a 1.7-liter capacity to optimize efficiency). When incorporating the Mannol 9903 additive, combine 2.0 liters of fresh gear oil with the 50ml additive. This total volume of 2.05 liters safely matches the standard maintenance target while remaining well below the maximum dry overhaul capacity.

Mannol 9929 Profile: Third, regarding Mannol 9929 (Ester Additive): Mannol’s official website states that 9929 is an "additive to engine oils and to oils for mechanical transmissions". While highly fluid and possessing a high viscosity index, its core chemical package is optimized for internal combustion environments, containing ZDDP and heavy detergents designed to prevent deposits of lacquers, resins, and sludge. At a 5% to 10% mixing ratio, adding these components to a dedicated PSA B71 2330 gear oil risks altering the precise friction coefficient required by the synchronizer rings. If the friction baseline shifts, it can delay synchronization windows, causing the automated TCU shifting logic to register sluggish engagement or actuator stress. Furthermore, these engine-specific detergents can actively compete with the transmission's native Extreme Pressure (EP) surface additives.

Mecarun P18 Profile: Fourth, regarding Mecarun P18: While Mecarun P18 is also marketed for universal applications ("for engines, manual and automatic gearboxes"), its chemistry differs fundamentally from Mannol 9929. P18 is not an engine oil concentrate with detergents; it is a highly refined hydrocarbon-based friction modifier engineered to form a micro-thin boundary tribofilm on metal surfaces under heat and pressure. It does not introduce engine-specific cleaning detergents or risk thickening the fluid layout. However, in a computer-controlled robotized transmission like the EGS6, applying a highly potent anti-friction surface treatment at a standard 4% ratio still introduces an operational variable. Because the TCU monitors synchronizer engagement down to milliseconds, making the synchronizer rings excessively slick can cause them to slide rather than grip properly, potentially triggering delayed synchronization codes.

Universal LS Limitations: Fifth, regarding Universal API GL-4/GL-5 LS (Limited Slip) Oils (e.g., Mannol Unigear 75W-80): Many universal gear oils list the PSA B71 2330 specification alongside "API GL-5 LS" on the bottle. While modern additive chemistry can technically balance GL-5 shear protection with synchromesh compatibility using inactivated sulfur, the "LS" (Limited Slip) designation introduces a critical mismatch for automated manual gearboxes. Limited Slip additives utilize potent friction modifiers specifically engineered to allow wet clutch packs inside a limited-slip differential to slide smoothly and prevent chatter. In an EGS6 gearbox, the synchronizer rings act as mechanical brakes that must instantly grip the gear cone to match shaft speeds within milliseconds. Introducing a fluid chemically modified to prevent friction surfaces from grabbing directly opposes the transmission's synchronization requirements. Any extended synchronization slip can trigger immediate shifting faults, shift logic delays, or actuator timeouts.

Fluid Recommendations: Sixth, the best approach for the EGS6 gearbox is to avoid universal multi-vehicle lubricants, engine-targeted packages, or combined API GL-4/GL-5 formulations. While a standard 2L refill of the older PSA B71 2330 specification works (such as TotalEnergies Traxium Gear 8 or Fanfaro Max 7), the ultimate setup for a high-mileage unit is 2L of a fluid meeting the newer, more advanced PSA B71 2315 specification, topped up with 50ml of transmission-specific Mannol 9903 Getriebeoel-Additive. This combination ensures exceptionally fast actuator response during freezing winter mornings thanks to the lower viscosity and superior base oil of the 2315 standard, while the Group V esters from the 9903 provide a permanent, high-strength boundary layer on the gear flanks when hot. Prime examples for the 2315 base are Shell Spirax S4 G 75W-80 or Ravenol PSA SAE 75W-80, which are pure API GL-4 oils; these should not be conflated with API GL-5 fluids carrying the same approval (such as the Liqui Moly variant), as pure GL-4 chemistry is critical to preserve proper synchro friction.

Maintenance and Myths: Finally, ignore GearboxList (gearboxlist.com); there is no internal fluid filter, and while the core hardware is incredibly robust and can exceed 300,000 km on factory fluid under gentle driving, regular maintenance is vital to counteract the architecture's native flaws. In real-world operation—particularly in platforms like the Citroën C4 B7 and Peugeot 3008—the EGS6/ETG6 TCU logic is notorious for becoming jerky, hesitant, and twitchy over time. Because the automated system relies on millisecond-accurate sensor feedback (selector position, shaft speed) and high-cost electromechanical actuators, any degradation in fluid friction parameters directly accelerates these drivability issues and increases component stress.

Interval Recommendation: To maintain factory synchronization windows, ensure noticeably smoother gear shifting, and prevent premature wear and humming on the internal differential and output shaft bearings, a fluid exchange every 200,000 km is recommended. Note: This applies to the mechanical gear oil, not the separate Tutela CS Speed hydraulic fluid used in the external actuator reservoir.


Crucial Driver Operating Guidelines to Prevent Transmission Stress
Gear Selection Errors During Driving

1. Engaging Reverse (R) before the car has completely stopped
Problem: Forces the reverse gear components to mesh while rolling, which creates severe mechanical grinding and wear.
Solution: Always wait 1–2 seconds after the car is completely stationary before shifting to Reverse.

2. Engaging Forward (A/M) while the car is still rolling backward
Problem: Forces the clutch and internal gear trains to abruptly counteract the car's rearward kinetic movement, causing unnecessary stress.
Solution: Use the footbrake to stop all movement before changing travel directions.

3. Rocking the car back and forth when stuck in snow or mud
Problem: Rapidly throwing the shifter between forward and reverse causes severe clutch slipping and risks overheating the electronic clutch actuator.
Solution: Keep the car locked in either 1st or Reverse, apply gentle, steady throttle, and use external traction aids if the car remains immobilized.

4. Constantly downshifting manually with paddles at very high RPM
Problem: Forces the synchronizers to aggressively brake the input shaft speed to match high engine speeds, accelerating normal wear.
Solution: Let the TCU execute downshifts automatically during deceleration, or manually downshift only at lower, reasonable engine speeds.

Gas and Pedal Handling

5. Aggressive throttle inputs during an ongoing gear shift
Problem: Stomping on the gas pedal exactly when the robot is interrupting torque confuses the software and can lead to a jerky, poorly timed engagement.
Solution: Maintain steady, predictable pedal pressure and allow the robot to complete its automated shift cycle smoothly.

6. Flooring the gas pedal directly from a standstill
Problem: Forces the automated clutch to slip aggressively under heavy load to prevent the engine from stalling, causing rapid clutch wear.
Solution: Roll away smoothly for the first few meters to let the clutch fully engage before applying wide-open throttle.

7. Pumping the accelerator pedal during acceleration
Problem: Confuses the transmission control unit (TCU), causing it to hesitate, hunt, and cycle-shift between gears unnecessarily.
Solution: Hold a constant, linear foot position so the software can properly calculate, select, and lock the correct gear.

8. Pressing the brake pedal while simultaneously applying throttle
Problem: Confuses the transmission ECU, leading to conflicting commands where the system tries to engage the clutch while the brakes resist, overheating the clutch.
Solution: Drive strictly with one foot, ensuring completely separated brake and throttle inputs.

Cold Start Management

9. Starting the engine instantly without letting the hydraulic pump build pressure
Problem: Cranking the engine immediately after entering forces the hydraulic system to work before the system has reached its optimal operating pressure.
Solution: Unlock the car or open the driver’s door to trigger the automatic pump priming, turn on the ignition, and wait a few seconds for the buzzing sound to completely stop before cranking the engine.

10. Aggressive driving and high RPM before the engine and gearbox are warm
Problem: Heavy acceleration before the fluids reach operating temperature prevents optimal lubrication and increases wear on moving parts.
Solution: Drive gently, keeping engine speeds below 2500 RPM for the first few minutes of every journey.

Overloading and Towing

11. Towing a trailer heavier than the car’s maximum rated capacity
Problem: The extreme weight forces the automated clutch to slip excessively during take-offs and generates fatal heat buildup inside the gearbox clutch housing.
Solution: Strictly adhere to the manufacturer's towing limits or use a conventional manual vehicle for heavy hauling.

12. Driving with heavy loads up steep inclines in a gear that is too high
Problem: Refusing to downshift bogs down the engine and forces the clutch to endure maximum torque load under low RPM.
Solution: Manually drop a gear using the paddles to keep engine RPMs in an efficient range, ensuring proper power delivery.

Protecting the Drivetrain against Road Hazards

13. Speeding over speed bumps and deep potholes while applying throttle
Problem: When the front tires momentarily lose traction and suddenly regain grip upon landing, a severe torque shockwave is sent backward through the driveshafts into the differential.
Solution: Complete all braking well before the hazard, and coast over bumps with your foot off the pedals so the drivetrain is torque-free during impact.

14. Accelerating hard on uneven surfaces (gravel, washboard roads, ice)
Problem: When the tires repeatedly lose and suddenly regain grip, it sends rapid torque-snaps directly into the differential and internal gear train.
Solution: Ease off the throttle and maintain a steady, low-load speed over loose or icy ground.

Parking and Diagnostics

15. Relying solely on the transmission to hold the vehicle on steep inclines
Problem: The EGS6 gearbox does not possess a mechanical parking pawl (P). If turned off in N, it rolls freely. If turned off in A/R, the car's mass pulls against the internal gear teeth and dual-mass flywheel.
Solution: Always apply the Electronic Parking Brake (EPB) firmly to absorb the vehicle's weight, and leave the gear selector in A (or R) as a secondary mechanical backup.

16. Ignoring transmission warning lights and continuing to drive
Problem: Disregarding a "Gearbox Fault" message can turn a minor, easily fixable electronic glitch or low fluid level into major mechanical damage.
Solution: Pull over safely, turn off the engine, and have the system diagnostic-scanned (preferably with a Diagbox/Lexia scanner) immediately when a fault light appears.

Tires and Differential Protection

17. Driving with mismatched tire dimensions on the driven axle
Problem: Using a wrong-sized tire alters wheel speed readings, which tricks the ABS/ESP sensors and forces sudden, jerky, or mistimed automatic shifts.
Solution: Only use identical tire sizes across the driven front axle.

18. Driving with severely uneven tire pressure on the front axle
Problem: Creates a constant rolling speed difference between the two wheels, forcing the internal differential gears to work continuously even when driving perfectly straight, creating heat.
Solution: Check and equalize front tire pressures regularly.

City Driving and Traffic Jams

19. Creeping in heavy traffic
Problem: Continuous creeping causes the EGS6 gearbox (Citroën C4 B7 2013 / Peugeot 3008 2012) to slip the clutch under 6–7 km/h in 1st gear and 13–15 km/h in 2nd gear. This creates a dangerous overlap where clutch slip and engine lugging occur at the same time, generating extreme heat and destructive engine vibrations.
Solution: Switch to Manual mode (M) and lock the gearbox in 1st gear, or use the downshift paddle while in Automatic (A) mode to force a downshift to 1st gear. This eliminates clutch slip and protects against engine lugging. Allow a gap to form ahead, then accelerate past 10 km/h to lock the clutch completely.

Advanced Driving Techniques

20. Holding the car stationary on an incline using only the accelerator pedal
Problem: Forcing the engine to hold the vehicle's weight on a hill without pressing the brake pedal causes the electronic clutch to constantly slip at high friction, causing extreme heat and burning the clutch lining within minutes.
Solution: Use the vehicle's built-in Hill Assist feature, or apply the handbrake until you are ready to accelerate away cleanly.


(Rustprevention: Older cars are highly susceptible to rust, so when the car is dry it should be inspected from all angles, including underneath. To protect the vehicle from rust damage, first scrape away loose rust, apply a rust converter to the remaining pores, and apply a base layer of 2K epoxy primer directly after the rust converter to create a superior, impenetrable barrier compared to standard 1K bases. Next, apply the 1K touch-up paint matching the car’s color code in multiple layers without sanding between them, as sanding the wet or fresh basecoat will ruin the metallic pigments. Once the color coat is dry, seal the repair by applying 2–3 wet, cross-coated layers of 2K clear varnish via spray or brush, allowing only a few minutes of flash-off time between coats without any sanding so the droplets can fuse into a solid, glossy plastic shield with no microscopic gaps; this completely blocks new moisture and road salt from penetrating from the outside. Only after the final 2K clear coat has fully cured for several days may you use an ultra-fine P2000–P3000 wet sandpaper to level out any dust or orange peel before polishing it to a mirror finish, while an elastic underbody coating should be used underneath the chassis instead of 2K clear varnish.)

[frer8833]

Definitive EGS6 (MCM) Guide: Gearbox Oil Paradox, Actuator Upgrades, and Additives Correction

To follow up on my previous posts regarding EGS6 (MCM/BVMP6) transmission maintenance, I need to make an important correction regarding the Mannol 9903 additive, and also cover the actuator fluid.

First, a correction on the Mannol 9903 additive. In my previous post, I recommended mixing 50ml of Mannol 9903 Getriebeoel-Additive with the newer PSA B71 2315 specification gear oil. This is incorrect. The 50ml of Mannol 9903 is only needed if you use the older PSA B71 2330 gear oil (like Total Traxium Gear 8) to boost its extreme pressure wear protection. If you upgrade to the newer 2315 spec oil, do not use the additive. Fresh 2315 oils already have advanced chemical packages, and adding extra friction modifiers risks altering the precise friction coefficient required by the brass synchronizer rings. This can confuse the robot's millisecond timing. In short: the additive is great for 2330 oil, but 2315 oil should be run pure.

Furthermore, upgrading the mechanical gear oil is highly important for the EGS6 shifting behavior. Worn-out gear oil causes the synchronizer rings to slip. The TCU monitors this speed match down to milliseconds. If synchronization is delayed, the computer pauses the shift to protect the gear teeth, which causes the classic hesitation or pause on warm days. Fresh gear oil lets the synchros bite immediately, eliminating this pause and making shifts quiet and responsive.

However, the EGS6 transmission has a completely separate electro-hydraulic actuator (robot) sitting on top of the mechanical gearbox. They use different fluids in separate reservoirs. If your car still hesitates on freezing cold days, or suffers from jerky take-offs and clutch judder, you need to change the actuator fluid as well.

PSA B71 2315 vs. B71 2330: Spec Sheets vs. Reality

The PSA B71 2315 specification (like Shell Spirax S4 G 75W-80) was introduced to replace the older 2330 mineral oils to improve winter shifting and fuel economy by lowering the operating viscosity. Under normal circumstances, a standard 2315 fluid flows easier than standard 2330 mineral oils.

However, Ravenol MTF-2 SAE 75W-80 (Article No: 1221103) is an exception. Even though MTF-2 is classified under the older B71 2330 standard, its laboratory parameters are heavily over-engineered compared to standard semi-synthetic 2315 fluids (like Ravenol Getriebeoel PSA SAE 75W-80, Art No: 1222100).

Data sheet comparison:
- Viscosity at 100 degrees Celsius: MTF-2 is a thicker 9.1 mm2/s. Ravenol PSA 2315 is 8.5 mm2/s. Shell Spirax is 8.7 mm2/s.
- Viscosity at 40 degrees Celsius (Warmup): MTF-2 is 50.8 mm2/s. Ravenol PSA 2315 is 43.1 mm2/s. Shell is 47.0 mm2/s.
- Brookfield Viscosity at -40 degrees Celsius: Despite being thicker at room temperature, MTF-2's advanced PAO base means its viscosity in extreme freezing conditions is only 21,900 mPas, while Ravenol PSA 2315 is more than twice as thick at 52,500 mPa·s.
- Pour Point: MTF-2 flows down to -51 degrees Celsius. Ravenol PSA 2315 stops at -39 degrees.
- Viscosity Index (VI): MTF-2 is 163. Ravenol PSA is 178. Shell is 166.
- Flashpoint: MTF-2 is 248 degrees Celsius. Ravenol PSA is 234 degrees. Shell is 216 degrees.

Why is Ravenol PSA VI 178 but worse in extreme cold? VI is calculated only between 40 and 100 degrees Celsius and does not measure sub-zero behavior. Ravenol PSA is a semi-synthetic using a solvent-refined Group I/II mineral base, which naturally contains trace amounts of paraffin (wax). In the cold, the wax crystallizes and the oil gels, making it thick (52,500 mPa·s Brookfield). MTF-2 is a pure Group IV PAO synthetic with zero wax, so it does not gel and stays fluid in the cold (21,900 mPa·s).

Also, Ravenol PSA relies on polymer Viscosity Index Improvers (VIIs) to reach 178 VI. These polymer chains shear (chop up) under mechanical stress, causing the VI to collapse over high mileage, which is why a 200,000 km exchange interval is recommended. MTF-2's 163 VI is natural to its PAO base, meaning it is highly shear-stable and will not degrade. For context, standard mineral-based 2330 fluids like Total Traxium Gear 8 have a poor Viscosity Index of 130-137 and a thick Brookfield viscosity of 104,000 mPa·s at -40C. Another example is Mannol 8104 MTF-4, which has a KV40 of 48.96 cSt and a VI of 142. Despite Mannol's marketing claiming "superior low-temperature properties... down to -30C", its actual lab-measured Brookfield viscosity at -40C is a massive 120,500 mPa·s. Fanfaro Max 7 also sits at a poor VI of 140 and hides its Brookfield numbers entirely. These standard mineral-based oils act like cold grease in the winter compared to MTF-2's exact, lab-proven 21,900 mPa·s.

Why isn't MTF-2 classified as 2315? Because PSA's B71 2315 specification strictly demands a slightly thinner viscosity profile (around 8.5 mm2/s at 100C) to optimize fuel economy. MTF-2 prioritizes maximum gear-flank protection and extreme-load stability (meeting heavy-duty specs like BMW MTF-LT-2 and Volvo) over thinness, resulting in its robust 9.1 mm2/s profile.

There is also no reason to fear running a B71 2330 oil in these gearboxes. When the EGS6 (MCM) transmission was manufactured in 2012, it left the factory filled with B71 2330 oil (such as Total Transmission BV). The synchronizers, gear clearances, and shift logic were physically calibrated for 2330 viscosity. While PSA later superseded this with 2315 primarily to meet newer European emissions regulations, running a premium, over-engineered 2330 like Ravenol MTF-2 is actually closer to the gearbox's original design targets, with the added benefit of a thicker fluid cushion for older gearsets.

Real-world Warmup: Calculated Viscosity at +10C

While comparing cold flow at -40C shows the absolute limits of the base oil, a normal spring or autumn morning in Europe at around +10C is a much more realistic scenario. This is where the gearbox spends a significant portion of its warmup phase. At +10C, these fluids are far from their wax-crystallization or pour points. The viscosity curve follows the 40C and 100C data sheets linearly. The fluid with the lowest viscosity at 40C and the highest Viscosity Index (VI) will flow the easiest. In data sheets, dynamic viscosity in mPa·s (Brookfield) is usually only measured at sub-zero temperatures. However, for positive temperatures, we can calculate the exact dynamic viscosity (mPa·s) by multiplying the kinematic viscosity (mm²/s or cSt) at that temperature by the oil's density (g/cm³).

Here is the ranking based on mathematical interpolation from the official data sheets, ordered from thinnest (best flow) to thickest:
1. Ravenol Getriebeoel PSA SAE 75W-80 (B71 2315)
- KV40: 43.1 cSt | VI: 178 | Density: 0.843 | Pour Point: -39C
- Calculated value at +10C: approx. 135–140 mPa·s
- Brookfield Viscosity at -40C: 52,500 mPa·s
2. Shell Spirax S4 G 75W-80 (B71 2315 - International Spec)
- KV40: 47.0 cSt | VI: 166 | Density: 0.891 | Pour Point: -45C
- Calculated value at +10C: approx. 170–180 mPa·s
- Brookfield Viscosity at -40C: Not published by Shell (SAE 75W limit: max 150,000 mPa·s)
3. Ravenol MTF-2 SAE 75W-80 (PAO / B71 2330)
- KV40: 50.8 cSt | VI: 163 | Density: 0.847 | Pour Point: -51C
- Calculated value at +10C: approx. 190–200 mPa·s
- Brookfield Viscosity at -40C: 21,900 mPa·s
4. Mannol 8104 MTF-4 75W-80 (B71 2330)
- KV40: 48.96 cSt | VI: 142 | Density: 0.850 | Pour Point: -46C
- Calculated value at +10C: approx. 195–205 mPa·s
- Brookfield Viscosity at -40C: 120,500 mPa·s
5. TotalEnergies Traxium Gear 8 75W-80 (B71 2330)
- KV40: 57.7 cSt | VI: 150 | Density: approx. 0.880 | Pour Point: -45C
- Calculated value at +10C: approx. 250–265 mPa·s
- Brookfield Viscosity at -40C: 104,000 mPa·s

Comparing the newer 2315 spec from Ravenol against the old factory standard Traxium Gear 8, the difference in fluid drag at +10C is clear. Total Traxium Gear 8 has a heavy resistance of around 250–265 mPa·s, while Ravenol PSA (2315) sits at just 135–140 mPa·s. At +10C, the Total oil is almost twice as thick. On a cool morning, the robot meets significantly higher fluid resistance when pushing the synchronizers with Traxium Gear 8. Ravenol PSA heavily reduces this internal drag during warmup.

Ravenol PSA draws benefit from two parameters simultaneously. It starts thinner at 40C (43.1 cSt vs. 57.7 cSt) and has a much higher Viscosity Index (178 vs. 150), allowing its viscosity to stay flatter as temperature drops. It also has a lower base density (0.843 vs 0.880), further reducing dynamic drag. At a standard +10C, Ravenol Getriebeoel PSA is the clear winner for flow, minimizing the hydraulic and mechanical load on the shift actuators during warmup.

This leaves EGS6 owners with two distinct, excellent pathways:
- Option 1 (The Indestructible PAO/Arctic Specialist): Run Ravenol MTF-2 (2330). Since the EGS6 was originally designed with the B71 2330 standard, its synchronizers and shifting logic are perfectly calibrated for this viscosity. Its premium PAO base oil offers unbeatable thermal limits (248C flashpoint) and exceptional fluidity in extreme sub-zero conditions (-40C Brookfield is only 21,900 mPa·s). Additionally, its slightly thicker hot viscosity (9.1 mm2/s) provides a protective cushion for worn, high-mileage gear flanks, and its shear-stable PAO base means its 163 VI will never degrade, making it the ultimate long-term choice.
- Option 2 (The Fast Warmup / OEM Spec Purist): Run Shell Spirax S4 G 75W-80 (or Ravenol Getriebeoel PSA). Shell provides the exact thinner B71 2315 viscosity (8.7 mm2/s), while Ravenol PSA (2315) offers the absolute thinnest viscosity at typical +10C warmup mornings (135–140 mPa·s vs. MTF-2's 190–200 mPa·s) at a lower price point. Just remember that these semi-synthetics rely on polymer VI improvers which will shear down over time, necessitating a 200,000 km exchange interval.

Note: Since both of these premium options are chemically optimized, run them completely pure without additives to avoid upsetting the friction coefficients.

Actuator Hydraulic Fluid: Spec Sheets vs. Real-world +10C Viscosity

The EGS6 is essentially two separate systems: the mechanical gears (lubricated by the 75W-80 gear oil) and the electro-hydraulic robot actuator on top (which operates the clutch and shifts the gears). They have entirely separate fluid reservoirs, but they must work in perfect harmony as equal partners.

While fresh gear oil perfectly restores the synchronizer speed and eliminates mechanical shifting hesitation, the hydraulic actuator fluid is what physically powers the robotic movements. Over the years, this fluid degrades, turns black, absorbs moisture, and fills with micro-debris over the years. When the fluid ages, the small electric pump struggles to build the required 40 to 50 bar of pressure quickly—especially on freezing winter mornings when the fluid becomes thick and sluggish. This prevents the hydraulic valves and clutch actuator from physically moving fast enough, leading to persistent cold-weather hesitation and clutch judder even after a gear oil change.

For those wanting the absolute lowest fluid resistance (lowest viscosity) in green color for fast, responsive gear changes on a typical +10C European morning, we can use ASTM D341 interpolation to find the exact kinematic viscosities (cSt) at +10C.

Kinematic viscosity ranking at +10C (from thinnest/fastest flow to thickest):
1. Motul Multi HF (Central Hydraulic Fluid, PSA 9979.A4 & Fiat 9.55550-SA1) / Pentosin CHF 11S (or Febi Bilstein 06161, PSA S71 2710)
- Base data: 18.7 cSt at +40C | VI: 313
- Viscosity at +10C: approx. 39.8 cSt
2. Ravenol GHA-F (Gearbox Hydraulic Actuator Fluid, PSA 9979.A4)
- Base data: 19.7 cSt at +40C | VI: 333
- Viscosity at +10C: approx. 40.5 cSt
3. Petronas Tutela CS Speed (Factory Fill, Fiat 9.55550-SA1)
- Base data: 24.22 cSt at +40C | VI: 270
- Viscosity at +10C: approx. 56.1 cSt

Why the factory oil causes a sluggish experience: Petronas Tutela has the lowest Viscosity Index (270) and starts the heaviest at +40C. At +10C, it thickens to 56.1 cSt, which is over 40% thicker than its rivals. This extra viscosity is what causes the actuator block to feel sluggish during the first few kilometers.

The thinnest fluids (Motul Multi HF, Pentosin/Febi 06161, and Ravenol GHA-F) are tightly grouped between 39 and 41 cSt. While Ravenol's high VI of 333 keeps its curve flat as it gets colder, Motul Multi HF and Pentosin CHF 11S take first place as the thinnest green fluids at +10C thanks to their low 40C starting point of 18.7 cSt. With any of these top fluids in the actuator reservoir, the hydraulic pump faces less resistance, leading to faster pressure accumulation (reaching the 40-50 bar target quicker on startup) and more exact solenoid valve modulation. Because the thinner, high-index fluid flows faster through the microscopic valve channels when cold, it heavily reduces the cold-weather shifting hesitation or clutch judder before the system reaches operating temperature.

Note on parts database compatibility (such as Autodoc): In the official Peugeot/Citroën service manual, the EGS6 actuator is classified as a "closed, lifetime-filled" unit. Therefore, parts catalogs like Autodoc completely lack an official category for EGS6 actuator fluid. This leads to major database paradoxes. First, if you search for Petronas Tutela CS Speed (the actual factory-fill fluid), it will not list the PSA 9979.A4 specification on the site. This is because Petronas only labels the commercial bottle with the original Fiat 9.55550-SA1 standard (which PSA's robot supplier, Magneti Marelli, designed the system for). In reality, Fiat 9.55550-SA1 and PSA 9979.A4 are completely interchangeable because the EGS6 and the Fiat Selespeed are the exact same Magneti Marelli hydraulic robot. Second, if you search for Febi Bilstein 06161 or Pentosin CHF 11S, they will show as "compatible" simply because they are cataloged under the vehicle's electro-hydraulic power steering (EHPS) system, which also officially requires the PSA S71 2710 standard. PSA S71 2710 is Peugeot/Citroën's master specification for synthetic central hydraulic fluids. While Febi 06161 officially lists PSA S71 2710 (alongside other hydraulic specs like PSA 9979.64 and 9979.69), it does not list the EGS6 clutch actuator spec (PSA 9979.A4). However, because both the EHPS steering and the EGS6 actuator are high-pressure systems designed by the same suppliers using the exact same internal rubber seals, these green central hydraulic fluids are chemically compatible and can be used interchangeably in the actuator, bypassing the database limitations while maintaining perfect green color compatibility.

Why is Factory Tutela CS Speed Thicker? The Defensive Trade-Off

If fluids like Motul Multi HF and Pentosin CHF 11S flow faster at both +10C and sub-zero temperatures, why did Petronas and PSA optimize Tutela CS Speed to be thicker? The answer lies in defensive engineering. When designing the EGS6 actuator, PSA and Petronas prioritized high-temperature pressure stability and mechanical component longevity over extreme cold flow:

First, high-temperature internal leakage protection. The EGS6 actuator operates under high pressure (40-50 bar). Under heavy motorway driving or stop-and-go summer traffic, the hydraulic block gets extremely hot. At high temperatures, a fluid that starts very thin becomes highly volatile and thin. This increases the risk of internal bypass leaks through the solenoid valves and seals. If pressure drops due to internal leakage, the electric pump must run much more frequently to maintain pressure, accelerating pump wear. Tutela's heavier startup profile (24.22 cSt) ensures sufficient fluid "body" to maintain pressure stability when scorching hot.

Second, anti-shudder friction additives. Unlike central hydraulic fluids (CHF) like Febi 06161 (which are highly engineered, fully synthetic fluids but designed primarily for steering and suspension), dedicated actuator-spec fluids like Tutela CS Speed (Fiat 9.55550-SA1), Ravenol GHA-F (PSA 9979.A4), or Motul Multi HF (which officially carries both PSA 9979.A4 and Fiat 9.55550-SA1) contain a specific friction modifier package. This package is tailored to provide linear, predictable friction inside the clutch slave cylinder to prevent stick-slip (shudder or judder during engagement). Power steering fluids do not require these specific clutch-modulation additives as steering racks never operate clutch pistons.

Third, extreme shear stability under pressure. Every gear shift forces the hydraulic fluid through microscopic solenoid orifices under 50 bar of pressure. This extreme mechanical shearing literally chops up polymer chains. Petronas formulated Tutela CS Speed with highly shear-stable molecules to withstand thousands of high-pressure shifts without losing its original viscosity.

Therefore, EGS6 owners must decide on a maintenance philosophy:
- The Factory Defensive Setup (Tutela CS Speed): Optimized to work acceptably under all conditions—from an Arctic winter to Sahara heat—without losing pressure stability or shearing down over the manufacturer's nominal lifetime. It sacrifices responsiveness at +10C to ensure zero leakage at +100C.
- The Low-Temperature / Cold-Start Setup: Optimizes for daily cold-start responsiveness, which is the primary drivability issue in temperate/Northern European climates. These premium synthetic fluids are fully compatible with PSA's high-pressure actuators and seals. Motul Multi HF is the premium choice. It officially carries the PSA 9979.A4 and Fiat 9.55550-SA1 approvals, meaning its fully synthetic shear stability and chemical life are certified for the entire lifespan of the transmission without any abnormal pressure loss.

Another critical warning is the "Color Chaos" issue: Original Tutela CS Speed and Febi 06161/Pentosin/Motul Multi HF are green. Orange or red fluids (like Total Fluide LDS and Fluide DA) must be completely avoided in this specific system. Because the EGS6 actuator block is highly complex and impossible to drain 100% without complete disassembly, residual green fluid will remain in the system. Mixing green and orange/red hydraulic fluids turns the mixture into a dark brown, muddy-colored fluid. This makes future visual inspections of the fluid condition impossible, as you will not be able to see if the oil has darkened from wear, absorbed water, or accumulated microscopic metal shavings.

Warning: Depressurize Actuator System Before Fluid Change

Do not attempt to simply extract the actuator fluid from the plastic reservoir. The system operates at 40-50 bar, and a large portion of the fluid is stored under high pressure inside the accumulator sphere.

You must use PSA Diagbox / Lexia (or an advanced bi-directional diagnostic tool like Kingbolen Ediag / Launch) to run the "Depressurise hydraulic circuit" command first. This electrically opens the valves and forces all the fluid inside the accumulator back into the plastic reservoir so you can see the true maximum fluid level. Extract the old fluid, and fill with fresh actuator fluid to the MAX line. If you top off a pressurized system, it will violently overflow later when the system rests and the pressure drops. After refilling, prime the pump (e.g. by opening the driver's door) to rebuild pressure, and check for leaks.

EGS6 Maintenance Setup

Summary for EGS6 setup:
1. Drain and refill the mechanical gearbox with exactly 2.0 to 2.1L of a high-performance oil. Your two best pathways are either the ultra-premium PAO-based Ravenol MTF-2 75W-80 (for maximum gear protection and shear stability) or a dedicated B71 2315 oil like Shell Spirax S4 G 75W-80 or Ravenol Getriebeoel PSA SAE 75W-80 (for the thinnest warmup flow and exact OEM specification).
2. Depressurize the actuator, extract old fluid, and refill reservoir with fresh green fluid. The system holds around 0.9L of fluid in total, but a standard reservoir drain and refill will extract about 0.5L to 0.6L. Therefore, a single 1L bottle of Motul Multi HF (for the absolute best, fastest winter response in green with official PSA 9979.A4 and Fiat 9.55550-SA1 specifications) is more than enough. Alternatively, you can use Pentosin CHF 11S / Febi Bilstein 06161 (for the same extreme flow under master steering specs) or Ravenol GHA-F / Petronas Tutela CS Speed.
3. Perform a Diagbox clutch bite-point and grid re-adaptation to restore shifting smoothness instantly. However, this is not strictly mandatory, as the TCU is self-learning and will slowly adapt to the new fluid over time on its own.

The Ultimate Real-World Combination (Fastest Response):

For standard driving climates, the absolute fastest-flowing setup is Ravenol Getriebeoel PSA SAE 75W-80 in the gearbox combined with Motul Multi HF in the actuator. This combination provides the absolute lowest fluid drag, fastest synchronizer engagement, and quickest hydraulic response during cold starts and warmup while maintaining perfect fluid color compatibility within the actuator reservoir (both the factory Tutela and Motul Multi HF are green) and official manufacturer specifications.


Official Technical Product Data Sheets (TDS) for reference:

- Ravenol MTF-2 SAE 75W-80 (B71 2330 / PAO Full-Synthetic): https://ravenol.de/storage/app/media/pr ... 103_en.pdf
- Ravenol Getriebeoel PSA SAE 75W-80 (B71 2315 / Semi-Synthetic): https://www.ravenolitalia.it/wp-content ... 222100.pdf
- Shell Spirax S4 G 75W-80 (B71 2315 / Group III): https://www.shell-livedocs.com/data/pub ... 6eaf81.pdf
- Total Traxium Gear 8 75W-80 (B71 2330 / Mineral-Synthetic technology): https://total-cdn-lmdb.afineo.io/tdsV2/ ... TSH_EN.pdf
- Fanfaro 8710 Max 7 75W-80 (B71 2330 / Semi-Synthetic): https://sct-b2b.com/out/msds/sdFF8710_- ... 0_(IE).pdf
- Mannol 8104 MTF-4 75W-80 (B71 2330 / Synthetic technology): https://www.mannol.de/create-pdf/211/en https://zsu.hu/uploads/dokumentumok/MAN ... 90XuTn516L
- Ravenol GHA-F (PSA 9979.A4 / Selespeed Hydraulic Fluid): https://www.ravenol.de/storage/app/medi ... 201_en.pdf
- Petronas Tutela CS Speed (Fiat 9.55550-SA1 / OEM Actuator Fluid): https://epliportal.pli-petronas.com/ePl ... ageCode=EN https://epliportal.pli-petronas.com/ePl ... ageCode=EN
- Pentosin CHF 11S (PSA S71 2710 / Central Hydraulic Fluid): https://logistikportalen.fmv.se/tjanste ... PDS_SE.pdf
- Total Fluide LDS (PSA S71 2710 / Orange Hydraulic Fluid): https://totaloilnz.co.nz/technical-documents/4203.pdf
- Febi Bilstein 06161 (PSA S71 2710 / Central Hydraulic Fluid): https://cdn.partsfinder.bilsteingroup.c ... 0906_D.PDF
- Motul Multi HF (PSA 9979.A4 & Fiat 9.55550-SA1 / Synthetic Actuator Fluid): https://azupim01.motul.com/media/motulD ... 211022.pdf