temp problem

[SD1too]

Originally Posted by fraz59

I have the heater on since you said have the Econ button on, I presume it must be switched on for it to work correctly ..

This is the simple guide to the 75/ZT heating & air conditioning system:

Econ: air conditioning compressor switched off.
Auto: air conditioning compressor switched on.

Otherwise the system works in exactly the same way. Hot coolant passes at full flow through the heater whether 'Econ' or 'Auto' is pressed. All the temperature control is done by flaps controlling the airflow and the blower motor speed.

Originally Posted by T-Cut

It would be difficult to fit incorrectly with the standard pipework. The results don't indicate that. The evidence suggests the stat is permanently open.

Fraser says that his engine reaches normal temperature at idle and low speeds. At high speeds the temperature plummets. Could this be a fault in the 'pressure relief' side of the PRT? I'm not sufficiently confident that I fully understand the PRT to be sure.

Simon

[SD1too]

Originally Posted by fraz59

I did also check the old thermostat it worked as it should, opened when boiling water was poured in, and closed again with cold water .

Most thermostats are designed to open around 88° Fraser, so a boiling water test is invalid. You need to heat the 'stat up from cold with a thermometer in the water. But your test at idle when the coolant reached 105° proves that the conventional part of the PRT is working correctly. It's when the coolant flow increases that you get problems.

... now starting to suspect the head gasket ..

It's not the head gasket.

I read about people fitting another stat someplace on these engine ...

No, that's the diesel engine.

By the way, your expansion tank might be overfilled. The level should only be up to the internal 'MAX' marker. This is quite low down in the tank.

Which colour PRT did you buy, and is it brand new? There are three variations apparently, with different characteristics.

Simon

[fraz59]

Yes it is a wee bit high, but I doubt that is the problem

it was comma G48, was what the local place recommended, but looking at it may be the incorrect type

http://www.commaoil.com/passenger-ve...ducts/view/353

but since I have flushed it a few time s most if not all will have gone now, so again doubtful that is the problem

will see what happens when I flush it again..I am really scratching my head with this car


just seen MGJohn reply...Have also changed the CTS (Black one) and the hoses are hot,,,top hose very hot can barely touch it, heater both hoses are hot, the one hose at the bottom is cool

[kaiser]

Not knowing how you drive, where you drive and how cold it is, it is going to be difficult to say exactly what is wrong. But it would make sense to stop using the heater, and see what the results are.
The heater itself can provide a lot of cooling, and if you slipper and pipe around with the heater on, and maybe even the demist switched on, the engine will be cooled inside and outside of the cabin.
48 degrees sound ridiculously low though.
One thing for sure is that the head gasket in your car is not gone, no car will ever get colder with a blown head gasket.

Switch your heater off, make sure the radiator fan is not running (no AC or Demist) make sure the water in the coolant system is sufficient and come back and tell us what the temperatures are.
In the meantime, don't worry if the system is overfilled or what antifreeze to use, these items have of no bearing on the current problem. Flushing and re-filling is not the problem here, over cooling is, or a temperature sensor fault. You have to start thinking logically and not shoot at everything that can possibly move.

[SD1too]

Originally Posted by fraz59

... heater both hoses are hot, the one hose at the bottom is cool

"The one hose at the bottom"?

Can you be more specific Fraser? If you mean the large hose exiting the radiator at the bottom it should also feel hot; not quite as hot as the top hose, but definitely not cool.
If you do mean this hose, and it is cool to the touch, then the problem is the thermostat.

Please report back on this one question Fraser.

Simon

[fraz59]

Originally Posted by kaiser

Not knowing how you drive, where you drive and how cold it is, it is going to be difficult to say exactly what is wrong. But it would make sense to stop using the heater, and see what the results are.
The heater itself can provide a lot of cooling, and if you slipper and pipe around with the heater on, and maybe even the demist switched on, the engine will be cooled inside and outside of the cabin.
48 degrees sound ridiculously low though.
One thing for sure is that the head gasket in your car is not gone, no car will ever get colder with a blown head gasket.

Switch your heater off, make sure the radiator fan is not running (no AC or Demist) make sure the water in the coolant system is sufficient and come back and tell us what the temperatures are.
In the meantime, don't worry if the system is overfilled or what antifreeze to use, these items have of no bearing on the current problem. Flushing and re-filling is not the problem here, over cooling is, or a temperature sensor fault. You have to start thinking logically and not shoot at everything that can possibly move.

I do not drive like I am the Chauffeur with Miss Daisy in the back lol, and on the Motorway the speed is around the limit

Those pictures I posted are with the temp is set to high but the blower is not running and the econ button is on

the PRT I bought was this one http://www.dmgrs.co.uk/products/prt-...ries-pem100990

Will be going out to re flush thoroughly and try a flush additive, check the PRT

[T-Cut]

Originally Posted by SD1too

Fraser says that his engine reaches normal temperature at idle and low speeds. At high speeds the temperature plummets. Could this be a fault in the 'pressure relief' side of the PRT? I'm not sufficiently confident that I fully understand the PRT to be sure.

Yes that could be an explanation, but with three separate PRTs exhibiting the same effect, there's seemingly another underlying issue. The PRT operates like any standard thermostat until the engine revs increase above a certain point (it's actually the water pump's pressure differential). At that point, it progressively blends cool flow from the radiator with hot flow from the head. I believe the theory is that this reduces the thermal 'shock' across the head and thereby mitigates against HGF.

The proportion of each flow seems to vary with engine revs. Low revs, low hot bleed. High revs, high hot bleed. I suppose the proportions are calibrated for each PRT spring rate against the default water pumping capacity. Maybe it's the water pump that's the underlying factor? This engine has had two HGF episodes and it would be reasonable to suggest the water pump was replaced on one or both occasions. Maybe an unusual pump was fitted?

I've still not gotten around to making my PRT animation to help us understand the issues which seem to appear regularly from it. These 'stills' may help those interested in learning how the PRT works.

These are the flows









Exactly how the over-pumping theory stands up should be clear from these drawings - I think.

TC

[kaiser]

Originally Posted by T-Cut

Yes that could be an explanation, but with three separate PRTs exhibiting the same effect, there's seemingly another underlying issue. The PRT operates like any standard thermostat until the engine revs increase above a certain point (it's actually the water pump's pressure differential). At that point, it progressively blends cool flow from the radiator with hot flow from the head. I believe the theory is that this reduces the thermal 'shock' across the head and thereby mitigates against HGF.

The proportion of each flow seems to vary with engine revs. Low revs, low hot bleed. High revs, high hot bleed. I suppose the proportions are calibrated for each PRT spring rate against the default water pumping capacity. Maybe it's the water pump that's the underlying factor? This engine has had two HGF episodes and it would be reasonable to suggest the water pump was replaced on one or both occasions. Maybe an unusual pump was fitted?

I've still not gotten around to making my PRT animation to help us understand the issues which seem to appear regularly from it. These 'stills' may help those interested in learning how the PRT works.

These are the flows









Exactly how the over-pumping theory stands up should be clear from these drawings - I think.

TC

No, T-cut that does not make sense. The flow can only go in one direction, you can't suddenly get flow back from the head against the pump direction.

The sprung disk is only there to seal the return into the block. So how it works, in you drawing, is as follows. When cold, the thermostat is closed, and the engine returns the flow from the pump into the block. As the temperature increases, the thermostat opens and the little sprung disk gradually closes the return into the block, until, at fully open, all the water is returned to the radiator for maximum cooling.
Furthermore, I think your flows are reversed, but that I will leave to you, as I don't know where the pipes are attached. But normally the heat sensing part of the thermostat, the wax filled part, brown orange, in your drawing, would sit in the supply side of the water, thus on the pressure side of the pump, for obvious reasons. I know the 1.8 is a bit upside down in many respects, but I don't think they would have been making an exception here.
I believe the flows are reversed. However, if you have a diagramme of the 1.8 cooling system, then the pressure side of the pump will be on the tangential side of the pump, and the suction side is connected to the center of the pump, so you can check it.
In theory, it should even work in reverse, but I doubt it.
Check the rotation of the engine, the rotation of the pump, and the flow is given.

[T-Cut]

For those that don't know, here's how the PRT fits into the circuits with the internals added to go with the drawings..



Note that hot flow to the radiator top is only possible when the PRT opens and unlocks the circuit.

TC

[T-Cut]

Originally Posted by kaiser

No, T-cut that does not make sense. The flow can only go in one direction, you can't suddenly get flow back from the head against the pump direction.

I don't think that's what I said.

The sprung disk is only there to seal the return into the block - - - -

The PRT isn't like the KV6 and diesel stats. The sprung disk in this case is a pressure sensitive valve.

Read this:http://wiki.seloc.org/a/Pressure_Rel...ote_Thermostat

TC