Coolant flow diagram

[T16]

[QUOTE=DerekS;891121]

Originally Posted by wuzerk

I have been lurking , reading all these posts, and finally have been stirred up enough to add my own observation >>>>>>

I totally agree with you Wuzerk.

In times past, I used to find that after a particularly heated session (towing caravan usually) when the temperature went 'over the top', the waxstat failed apparently in the open position, cos the engine then took a long time to warm up. Fortunately they were easy to replace in the Maxis/1100/minis.
It was quite a usual occurrence, overheat the stat, even for a short time, and it had to be replaced

In the 75's, the stats may get overheated, and we are not aware of the fact, as the temp detector may be situated away from the stat housing .
(Guessing here as I dont know its exact position ).
.

Surely the only way a stat will overheat is if its failed closed? I thought they were designed to fail open, hence why we have so many diesels running cold.

[T16]

Originally Posted by T-Cut

So, we all still await that crucial temperature test on a failed stat. Until that's done (on several different samples hopefully) we're still guessing. My money's not on the spring tension, but I hope we'll see - sometime soon.

TC

Well, watch this space...Im changing my failed stat tonight!

I have a new method of doing it I am trying, without jacking the engine, or even moving the engine mount.

[James.uk]

T16, you seem to have missed the point, that being that 88 degrees is too cold for the engine to run efficiently, hence all the discussions about increasing the thermo opening temp, or finding some other way get the engine to run hotter.. innit.. ....
...

[Mike Noc]

Originally Posted by T16

Well, watch this space...Im changing my failed stat tonight!

I have a new method of doing it I am trying, without jacking the engine, or even moving the engine mount.

Did a water pump and then later a thermostat change without jacking the engine up. I did support it though as taking the top engine mount off gives you easier access and it doesn't take long to remove it.

Mike

[David340R]

Originally Posted by T16

Im slightly confused as to all the confusion over this!!

Its a BMW 88 Deg Stat, therefore the engine SHOULD be running at approx 88 degrees when up to temperature.

If its not, then the stat has failed, either partially or fully open.

As we know, you can have a failed stat even with the temp gauge appearing NORMAL on the dash.

As for all this "cool running" stuff... well, it can only be cool running if the stat has failed!!

If the engine starts to cool then a correctly working stat will start to close off, keeping the engine at the correct temp surely.

So all this hoohaa about cool running diesels and an overcooling rad etc etc cant possibly make any difference whatsoever, as a working stat should always keep the engine at the correct temperature.

My stepdads ZT has a correctly working stat, and it comes up to temperature and stays bang on the same temp give or take a degree or so.

This is surely the correct operation, and anythign else has GOT to indicate a failing stat....


This is how I see it anyway.

Bang on the nail IMO. If adding a stat (with a similar opening temperature) in the top hose increases running temperatures then it MUST be that the standard stat is no longer doing it's job. Whether it is stuck partially open or is opning early is pretty much irrelevent (though interesting).

Could you please try to get a photo of the inside of the thermostat housing when you change yours?

I can see the top hose stat is a handy/cheap short term fix to save replacing the standard stat, but if they are really proving so unreliable and the job is such a PITA then I think a PRT is a more suitable long term solution. The comments on the other massive thread about temperatures spiking over 90 before the thermostat opens are one of the things that concerns me.

The cream Freelander K series PRT (88C) is probably the most suitable off the shelf and there looks to be plenty of space for it behind the radiator. Some of the R75/ZT 1.8K PRT hoses might also provide a short cut to fitting, but the connections to the engine are in different places so it might needs some other hoses cutting to fit.

[HarryM1BYT]

Originally Posted by T16

Im slightly confused as to all the confusion over this!!

Its a BMW 88 Deg Stat, therefore the engine SHOULD be running at approx 88 degrees when up to temperature..

The engine can only get to 88C, if the stat is working correctly AND if there is a sufficient surplus of heat. Both are critical - the M47 and other modern diesels are very thermally efficient, there is just not much waste heat produced. In winter the use of the heater is often enough to take away all of the surplus heat, so that the stat does not achieve its opening temperature.

[wuzerk]

I can see the top hose stat is a handy/cheap short term fix to save replacing the standard stat, but if they are really proving so unreliable and the job is such a PITA then I think a PRT is a more suitable long term solution.

The 'top hose stat' is not a short term fix and there is no reason why they should be any less reliable than normal thermostats. Mine has been in use for 15 months now with no problems and, should it need changing, it will take about 15 minutes. What is a PRT?

[David340R]

Originally Posted by wuzerk

I can see the top hose stat is a handy/cheap short term fix to save replacing the standard stat, but if they are really proving so unreliable and the job is such a PITA then I think a PRT is a more suitable long term solution.

The 'top hose stat' is not a short term fix and there is no reason why they should be any less reliable than normal thermostats. Mine has been in use for 15 months now with no problems and, should it need changing, it will take about 15 minutes. What is a PRT?

A PRT is a Pressure Relief Thermostat. It's the remote thermostat fitted as standard to later K series powered cars (75 and ZT as well as Freelander and MGF), but has also been retrofitted to quite a few earlier models of these and other K series cars (e.g. S1 Elise). The main reason for fitting is to reduce the incidence of head gasket failures by giving much better control over the water temperature flowing into the engine, but it also gives the water pump an easier time (which is the pressure relief bit). At higher RPM if the pump is pushing against a closed thermostat it can lead to cavitation, which can eventually cause failure. This is one of the things that worries me long term about adding a R5 top hose thermostat - it will mean the water pump is always pushing against an extra restriction.

[T-Cut]

Originally Posted by David340R

This is one of the things that worries me long term about adding a R5 top hose thermostat - it will mean the water pump is always pushing against an extra restriction.

But it's not. Water pumps aren't running against a blind exit or a significant restriction. The heater circuit is always open and this buffers the output from the pump. The thermostat simply provides a second route (to the radiator) by acting as a branch line. Isn't this where we came in?

IMO a PRT wouldn't make the slightest difference to the problem and would be a complex task in itself.

TC

[HarryM1BYT]

Originally Posted by David340R

A PRT is a Pressure Relief Thermostat. It's the remote thermostat fitted as standard to later K series powered cars (75 and ZT as well as Freelander and MGF), but has also been retrofitted to quite a few earlier models of these and other K series cars (e.g. S1 Elise). The main reason for fitting is to reduce the incidence of head gasket failures by giving much better control over the water temperature flowing into the engine, but it also gives the water pump an easier time (which is the pressure relief bit). At higher RPM if the pump is pushing against a closed thermostat it can lead to cavitation, which can eventually cause failure. This is one of the things that worries me long term about adding a R5 top hose thermostat - it will mean the water pump is always pushing against an extra restriction.

The pump is not pushing against a closed closed thermostat, there is always a continuous main path for the pump to circulate coolant around the engine, FBH and heater. The thermostat only closes off or restricts the path via the radiator. The PRT on other engines is there to solve an issue unique to the petrol engines of over heating.

The diesel engine has no such issues, rather the problem is one of lack of sufficient heating. The OEM stat also benefits from being located in the flow of water from the engine, making it more responsive, whereas the mod of inserting it in the top hose considerably reduces its responsiveness - despite that, it would seem to work.