Thermostats - troubleshooting

[Rhothgar]

For reference purposes, if anyone should have any doubt about the veracity of this thread.

Here is a photo of my old thermostat (datestamped 07-94 coincidentally!).

The gap looks bigger on photo than in real life.



What you see in the photo is the sum of the entire gap on the 'stat. It is NOT like this around the whole circumference, just what you see.

Would've have thought it could have such an effect?

I think some Vikal will bring it back to life...

[white exec]

That's all it takes for valuable hot water to find its way out of the block/head, and head off towards the radiator. As it does so, unfortunately, cold water enters the block (and heater matrix) to replace it!
Good photo!

[Rhothgar]

I took one with a kitchen spotlight behind and it made it look as though it was open almost.

Well! It looked twice as bad as the uploaded photo which is a good representation.

The other issue I guess is the system is designed to operate at 1.4 bar and the loss of pressure may affect things.

[white exec]

Even with a leaky thermostat (or one completely missing) the system should still pressurise. It'll be the at same pressure in all parts of the system, simply because as it heats up the coolant expands and creates pressure. Pressure relief is provided by the pressure cap (radiator or expansion tank), and, as you say, is usually around 1.3∼1.4 bar. This also has the beneficial effect of raising the boiling point of the 'water' towards 130°C, which allows the engine to safely run at 90–100°C, where it's most efficient.

The only additional 'pressure' behind the thermostat is down to the water pump, shifting coolant round the system, and it does this at very little extra pressure — it's essentially just a centrifugal paddle.

Good time of the year to get the heater working again!

[Jetjockey]

Hello Peter.

Did you ever produce that guide for changing the C5 X7 Thermostat. That’s the 2ltr Hdi Exclusive Tourer?

Thanks,

[Peter.N.]

I haven't as there seemed no demand, but I will if you want it.

Peter

[Jetjockey]

If it’s not too much trouble please. I can’t find any info anywhere.

Thank you.

[Peter.N.]

Neither could I which didn't bode well, either no one has done one or certainly haven't published it if they did. Will try and do it today.

Peter

[Jetjockey]

It looks a bit of a bugger!!

Quick thought....... I fitted an in-line stat (modification) to the top hose of a friends Rover 75 t'other day, it had been running cold for the last two years. He hadn’t bothered fitting a new one as it involved jacking car up, removing wheel and arch liner, jacking engine, removing engine mounting, removing the water pump, and lots of porch and fiddle!
The mod took only 30 mins start to finish, and that included removal and refitting of the inlet manifold.
It worked a treat, returning the engine operating temp to 88°C.
I wonder if this might work with the C5??????

Hmmmm.

[white exec]

Just out of interest, could you post a link to that in-line device?
Not for one moment recommending it for our cars, but would be interesting to know more.

[Jetjockey]

Hello Chris.

Here’s the you tube link and it’s just as shown in the video. The parts (£9.99) come from DMGRS, an MG and Rover spares company.



Parts from here:-

https://www.dmgrs.co.uk/collections/the ... 89-degrees

[Peter.N.]

I wish I had known about that inline stat, I looked but couldn't find anything.

Peter

[Paul-R]

Wow! £45 for a £6 thermostat plus two jubilee clips. Those instructions must be printed in gold leaf on vellum.

[myglaren]

Thermostats are certainly not what I was brought up on.

[white exec]

My main reservation about the idea of just fitting an additional in-line 'stat is the unknown condition of the failed original. If by an chance it is unable to open completely, the two 'stats could have a restricting effect on coolant circulation, which might not be helpful. A small risk, admittedly. Also just don't like the idea of leaving the old one in without investigating.

Located a short distance along the top hose, it will also not be exposed to the full circulation temperature of the coolant in the block/head, but left in something of a non-circulating temporary 'dead-leg', made worse by the old 'stat still being in position. This will have an effect on how rapidly it opens, but might or might not be important.

The in-line unit looks very short and stubby. Would have liked to see some extra clamping length for inserting into the (maybe curving) top hose. Shame to have to cut one of those in any case.

Can see the appeal, but it looks something of a bodge. Not exactly cheap.