Diesel thermostat definative answer

[Thomas]

Ok here are my findings

I fitted mine this afternoon and ran the engine at 3000rpm whilst stationery, the temperature went up and up and up even higher than I thought it would and it peaked at 99 degrees! now I was alarmed at that but it steadily dropped to 90 and then went back up to 99 and repeated itself at that, after that I took it for a roadtest where it peaked at about 77 and didnt drop below 73, the outside temperature was minus 3 so I guess the windchill factor on the motorway was quite a factor, I havent blocked the hole in the thermostat up and just fitted it straight to the car, I was wondering how the temp would be in the middle of the summer if stationery at minus 3 it reached 99 although holding it at 3000rpm was obviously a factor!

[James.uk]

Is your fan working Thomas??
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[Thomas]

Originally Posted by James.uk

Is your fan working Thomas??
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It is yes..

[wuzerk]

Thomas: a strange set of readings there! First it stays shut for too long and then it seems to open for too long! Hope it settles down.


COLVERT: I have been running with an in line 'stat which has only a minute bleed hole built in with no problems for nearly two months.

STEVE B: Brilliant, that should add to your motoring pleasure!

[Thomas]

weird indeed, I am not really using the car at the moment and it was only out today because I fitted the thermostat but I shall monitor it and keep everyone posted!

[T-Cut]

Originally Posted by Thomas

ran the engine at 3000rpm whilst stationery, the temperature went up and up and up even higher than I thought it would and it peaked at 99 degrees! now I was alarmed at that but it steadily dropped to 90 and then went back up to 99 and repeated itself at that.

Well I guess that proves one thing. These engines are quite capable of producing enough heat to get into the optimal range (95-105C). In my personal opinion, it's a myth that these engines can't produce sufficient heat to get them into the 100C area. With an appropriate thermostat system, and maybe with draft exclusion, they obviously can. I guess your stat is at the upper end of the manufacturer's tolerance range.

I was wondering how the temp would be in the middle of the summer if stationery at minus 3 it reached 99 although holding it at 3000rpm was obviously a factor!

Summer will have an effect, but less than you expect I believe. Typical petrol engines run at 95-100C whether it's -3C or +30C outside. The cooling system is more than adequate to cope. In fact it's probably over-designed in the diesel since few owners have actually experienced the cooling system in operation.

TC

[James.uk]

If one wanted to fit a wiggly thing then a long undersized pop rivet would be an easy fix..
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[Mintee]

Originally Posted by T-Cut

Summer will have an effect, but less than you expect I believe. Typical petrol engines run at 95-100C whether it's -3C or +30C outside. The cooling system is more than adequate to cope. In fact it's probably over-designed in the diesel since few owners have actually experienced the cooling system in operation.

I agree. I doubt 'summer' will be a problem at all.

[Samuelle]

Originally Posted by BigRuss

I had certain reservations when I saw the stat fitted to Phil's car yesterday, although I was impressed with the ease of fitting, the look and quality of the stat housing and the neatness of how it fitted, I did wonder about it's suitability in controlling the temperature correctly.

Firstly there will be approx 10-15C difference in the temperature between the engine water jacket temperature (measured by the IPK/Scanguage) and the actual temperature in the top hose. (Add a second digital temp sensor/guage into the top hose and you'll see if you watch the two guages together you'll see exactly what goes on in the cooling system under all load conditions)

Another thing to consider would be the cooling effect of the airflow through the radiator hitting the alloy casing of the thermostat housing but suspect this would only be a small amount and with the car moving.

Looking at the original design the stat is fitted to the return, this will restrict the flow through the radiator then will allow an amount of cooled coolant into the engine before it shuts again. Fitting a stat to the outlet will allow a bigger slug of cooled coolant to be drawn into the engine before it's shut off by the thermostat (basically it will over-cool).

It may be better to locate the themostat into the return, it's something that needs a little more thought and ideally some accurate temperature readings need to be taken, but I'm sure a perfect solution cannot be far away.

Russ

I think you may be being a bit over cautious here. The bottome line is the temperature of the engine block rather than the temp of the coolant. The thermostats don't operate that acurately anyway, with a fairly large leway built into the system, and that is of course if you have an operating thermostat in the first place, which a lot of people don't. The thermostat mod is fitted just after the coolant exits the block IIRC, and I find it hard to beleive that there would be a 10-15C difference in this short distance. My previous car was a BMW E12, and on the excellent 'first fives' board there were some yanks who raced in some kind of classic class. some of them fitted second temp sensors to the top tube, and IIRC I don't recall any of them talking about a big temerature difference between the two sensors.

As to the extra slug of coolant you mention, I don't see what difference it would make if the thermostat is closing flow at the exit or inlet point. Surely either way it is going to stop flow? or am I missing something here? If I am missing something, and there would be an extra slug of cooler coolant, how much difference would that make to the temperature of the block anyway (as opposed to the temperature of the coolant)?

As to fitting the second therm to the inlet rather than the exit hose? Wouldn't the temp of the coolant just after it exits the block be closer to the temp of the standard therm that is integral to the block, than if it was fitted to a hose after the radiator but before the engine block?

[rossocorsa]

Originally Posted by Samuelle

As to fitting the second therm to the inlet rather than the exit hose? Wouldn't the temp of the coolant just after it exits the block be closer to the temp of the standard therm that is integral to the block, than if it was fitted to a hose after the radiator but before the engine block?

yes I was rather thinking that fitting the stat in the bottom hose might well encourage later opening of the stat as given that the rad is cooled and heat rises the bottom hose should be cooler than the top hose(???)