75 CDT - Engine too warm

[clf]

Originally Posted by catakate

clf,

Never had the time to check the temp prior to removing the in-line thermostat, it was too high for the lenght of my journey, I pulled it out as fast as I could.

Without the heater on max temp and speed, the engine just keeps getting hotter, I turned the heater on at 100 degrees, obviously something wrong somewhere.. Although a bit better at the moment, as per the update above, still can't find a speed to keep the engine happy and under 105 C.

No signs of life from the fan so far, unfortunately. I can only hope for the pipes tu unclog themself or I have another thousand miles to crawl from one carpark to the next

to check the fan works, turn on the windscreen demist option on the heater (assuming you have climate control/air con).

I was curious to the temp prior to fitting the inline stat rather than removing it (this will determine the condition of the original stat). With the temps you describe however, there is nothing that suggests anything scary though. They do seem strange though, but it could just be a failed sender (unlikely) or a plastic bag blown up onto the the grill. Although if it went beyond 105 I would become concerned, and would be happy at it running at between 85-92 degrees.

When you describe the gauge given you a heart attack, what happened? Did the red light come on? Did it reach the red, or quickly rise suddenly?

[NigelOBB]

The original stats can start working again


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[Avulon]

Originally Posted by catakate

I've been looking at the diagrams of the cooling system but can't tell for sure so here is the question: the original thermostat is blocking the coolant comming back from the radiator through the bottom hose, or have I got it completely wrong?

Correct. I believe it's also responsible for directing warm coolant to the cabin heater as well.

[klarzy]

Have you tested the temp probe for a fault??

Also I used to run mine with an in line stat at 92 and it ran like a dream...

[catakate]

Boy, getting to that thermostat is such a pita.

Many thanks to all of you guys for taking the time and sharing your thoughts.

The culprit was the original thermostat. Found intact, no structural damage, nice and shiny, almost like new, but irresponsive to temperature. Haven't had the time to trace the part number yet but chances are it's the original part.

So, after opening early for God knows how long, it gave up disabling the cooling system. It might be a one off but it might just as well be a disaster waiting to happen on all CDTs out there.

Bare in mind that the temperature gauge is useless, it's there only for esthetical reasons. The slightest move of the needle above horizontal should be treated as a serious warning but your engine might already be running too hot.

I was lucky it happened to me in below freezing temperatures. The outcome could have been completely different in anything above 20C.

My advice: take the damn thing off, now!

Happy motoring to us all

[T-Cut]

Originally Posted by catakate

The culprit was the original thermostat. - - - So, after opening early for God knows how long, it gave up disabling the cooling system. It might be a one off but it might just as well be a disaster waiting to happen on all CDTs out there.

An interesting development on the diesel thermostat story. We know how the wax in these ('Type 2') stats changes over the years to cause premature opening. When fully open, the wax has nowhere else to expand, but there's normally enough resillience in the rubber capsule to cope with potential overheat. However, if the wax continues to decompose, one wonders whether it reaches a situation where the stat's fully open before the maximum running temperature (the in-line one controlling this) is reached? This will create a hydraulic lock and a pressure increase within the capsule. This pressure will become irresistible if the temperature continues to rise. The rubber will give way at the seal around the piston and the wax will be expelled into the coolant. From that point on, the stat will assume the usual failed shut condition. That causes loss of flow and overheating. The lack of response from the failed stat when tested indicates loss of wax.

TC

[catakate]

Originally Posted by T-Cut

The rubber will give way at the seal around the piston and the wax will be expelled into the coolant. From that point on, the stat will assume the usual failed shut condition.

TC

Should that seal be round the thin shaft pointing into the case? None left on mine, found a little blob of something that looked more like gasket silicone, black. If that is all that keeps the wax inside, your theory in proven.

[T-Cut]

Originally Posted by catakate

Should that seal be round the thin shaft pointing into the case?

Exactly so.
If you're interested in the details and got a couple of hours free, there's a thesis on the whole thing here: https://the75andztclub.co.uk/forum/s...d.php?t=102943

None left on mine, found a little blob of something that looked more like gasket silicone, black. If that is all that keeps the wax inside, your theory in proven.

Seems so. That is until a better theory comes along.

EDIT: It also suggests your warning about potential trouble ahead for in-line stat engines is worth bearing in mind. It seems the saga hasn't ended yet.

TC

[catakate]

Originally Posted by T-Cut

It also suggests your warning about potential trouble ahead for in-line stat engines is worth bearing in mind. It seems the saga hasn't ended yet.

TC

I would have liked to find this warning next to the one about the plenum drains. Would be a lot easier to do the job in a garage while the maintenance work is done and could have a trouble free trip across the continent.

[T-Cut]

Originally Posted by catakate

I would have liked to find this warning next to the one about the plenum drains.

Yours is the very first report (that I've ready anyway) of this effect. As noted, your warning should be taken on board by diesel owners with in-line stats. On the other hand, it may never happen again.

TC