Coolant flow diagram

[HarryM1BYT]

Originally Posted by FrenchMike

I wonder if among people having had thermostat problems, how many
have had fan issue previously ?
May be related ?

In my case,no overheating ,genuine thermostat...

Mike

Mike, don't forget this is the diesel we are talking about - it doesn't suffer over heating. :xmas-smiley-004:

My fan's low speed was originally faulty, but the only over heating issue I suffered was that of the a/c - where the fan would trigger to high speed, rather than the engine over heating.

[FrenchMike]

Originally Posted by HarryM1BYT

Mike, don't forget this is the diesel we are talking about - it doesn't suffer over heating. :xmas-smiley-004:

My fan's low speed was originally faulty, but the only over heating issue I suffered was that of the a/c - where the fan would trigger to high speed, rather than the engine over heating.

Yes Harry,i know;

It was a simple question;
what is strange is as far as i know, nobody reported having tried to find
an explanation for example by putting it in boiling water ?
punctured bulb,weakened spring ...

Mike

[HarryM1BYT]

Originally Posted by FrenchMike

Yes Harry,i know;

It was a simple question;
what is strange is as far as i know, nobody reported having tried to find
an explanation for example by putting it in boiling water ?
punctured bulb,weakened spring ...

Mike

A punctured bulb would not explain it, because a puntured bulb would mean it would fail to open.

I seem to remember someone tested the weakening spring theory, by adding shims to it and it made no difference to the opening temperature (as I would expect).

It really does all point to some change in the properties of the wax.

[T-Cut]

The spring is simply a return mechanism for the piston. The strength of the spring is irrelevant to the opening temperature of the valve. When the wax melts, it expands so forcing the piston/valve outwards. The hydraulic pressure is immense and no spring could stop it. On cooling/contraction, the spring ensures an orderly and complete return to closed. It prevent the formation of vacuum cavities in the wax pellet, which would allow it to settle part open.

All 'faulty' stats examined by Jules (hundreds he says) are shut when removed. I don't think he's checked them for reduced opening temperature, but it would be an interesting thing to do.

TC

[Mike Noc]

Originally Posted by man of kent

All interesting comments which is why I asked the original question. There is something unusual about the coolant flow on the engine which is why the stat fails so often. Haven't a clue at this stage why! Until the actual flow and proximity of flow route changes and components is known we will not know why.

Just to put this into perspective, not all M47R thermostats fail, and other cars' thermostats often do fail. My CDT stat was still working well at 304k and my Dad's Astra failed at around 50k.

And there wasn't much difference in the time it takes to change them, as on the Astra the wheel, inner arch liner, engine mount, cambelt, crank and cam pulleys and front and rear cambelt covers all have to come off to get to the thermostat.

If its any comfort we are not alone with thermostat problems or the difficulty we have with changing them!

Mike

[T-Cut]

I think the probability with ageing stats is that they never fail to open, but do so at a lower than desirable temperature. This effect expresses itself as a lower than ideal running temperature and heater. Many owners accept this as 'normal for a diesel' and regard everything as standard. This has become clear as diesel owners on the forums read the thermostat threads and say 'mine's like that too' and decide to change things. The percentage of diesel owners (on the forums) who replace or modify their thermostat to find an increased running temperature is quite significant. I suspect there are many thousands of owners out there who simply put up with their poor heater as a normal diesel quirk. The question is about what's 'normal'?

TC

[ardvark]

I've asked this question before and I'm sorry for being a pain. If I top up the cooling res or expantion tank with neat antifreeze, will it mix with the rest of the cooling fluid after a few runs?

[man of kent]

The assumptions in the very long stat and no heater thread is firstly the stats do fail. I'm lucky in never having had a stat fail in nearly 50 years of motoring. This suggests that they do not fail often. Wax stats have been around for many years and by the number of threads on failure it would suggest the BMW stat is defective but, BMW would have changed it or is the 75 is different in some way? Wax stats have been in petrol engines and work fine. They are just designed to open at a set temperature and if the BMW stat opens early there has to be something opening it. Not all replacements can be BMW OEM parts surely. Do we know that the problem is the BMW OEM stat only? Has anybody had a BMW OEM stat fail and then replaced it with a non OEM part and that had the same failure mode? in this case its an engine or cooling related design fault.

Not all diesels run cool so perhaps there are well designed diesels and poorly designed ones. That would suggest that you can change the running temperature by design changes (more friction or load). What I find intersting is that by design you can make an engine less thermally efficient and as the BMW 'runs cool' and thus becomes fuel inefficient, why not design the engine to create more heat i.e more friction. It seems to me that BMW MAY have designed a thermally efficient engine and then found out too late in the programme that it was too efficient. Personally I am not convinced at this stage that the BMW is thermally efficient. As I said in a previous post did BMW come up with a frictionless design, the holy grail of engine design. I doubt it. other manufacturers have been designing diesels fior many many more years than BMW.

Can anybody create an accurate flow diagram and post it? The one on the first post in this thread is pretty hopeles. The issues with flow diagrams are that the amount of flow through each 'hole' is important. All bends also affect flow.

[T-Cut]

Originally Posted by man of kent

The assumptions in the very long stat and no heater thread is firstly the stats do fail. I'm lucky in never having had a stat fail in nearly 50 years of motoring.

What's your car's mileage? What does your OBD show as the typical running temperature?

TC

[bl52krz]

Originally Posted by T-Cut

What's your car's mileage? What does your OBD show as the typical running temperature?

TC

Hi T-Cut. Just to add more mystery to the "flow of coolant around the system". My engine pumps water around and through to the header tank as soon as it is started up through the small hose.!! After testing the running temperature on a run to Salcombe last year in the winter, the obd showed that it was running at between, 84-88 degrees, and considering how cold it was, -3 to -5 degrees, i thought it did quite well, the thermostat i mean. From my observation of the running of the water to the header tank as soon as the engine was started,i would have thought that the thermostat was running partly open. I always thought that the engine coolant only flowed round the engine, until the thermostat opened at the set temperature, whatever that may be, and allowed it to go to the radiator to be cooled. Non plussed at the flow diagram, and the flow of water to my rad on startup!!