928S from 1985 - Running hot

[PorscheCollecto]

Hi all,

Need some help/suggestions.
My Porsche 928S from 1985 with automatic transmission, is running hot. Within few minutes of driving (10-12 min) and not loading the engine at all, it has the temperature gauge needle in the dash hitting the second highest white line, and continues to go in between last white line and the red zone. It stayes in that area and doesn’t seem to go all the way in the the top of the red. But I’ve not dared to keep on driving long enough to test it fully.
I know the engine is HOT, because you can feel in when opening to the engine room, everything just feels too hot, so I’m 99,9% sure the gauge in the car is right.

Many things have been tried fixed but without fixing the problem:
- brand new water pump incl cam belt installed
- brand new thermostat installed (btw did test it before installing it)
- all coolant exchanged (btw using red coolant)
- tried to vent the system to avoid air trapped in the cooling system
- jumped the wires to the temperature switch on the radiator, to ensure the fan in front of the A/C condenser is running full speed at all times (didn’t change anything)
- verified that the coolant system isn’t leaking, so no coolant is lost.

I have probably done more, but can’t remember now…
BUT is obvious for me that I’ve got no clue what next to try, hence this post.

What would you try next to find the culprit?

Bug thanks in advance for all your advise.

BR
Chris

[Opelotus]

What condition is your radiator in? Have you verified there is no debris between the AC condenser and the front of the radiator?

When the fan runs (belt driven fan, or the electric fan), do you feel hot air coming off the radiator? Does it run hot at idle, or only when you are driving?

With the engine off, does the belt driven fan spin freely by hand? Or does it have some drag to it?

[harborman]

Stuck thermostat? Even if a new one? Are the radiator hoses both hot? Sounds like the coolant is not circulating through the radiator.

[harborman]

You don't know for sure what the engine temp is? Did you put the new thermostat in correctly, not upside down?

[76FJ55]

When you changed the thermostat did you also replace the rear thermostat seal? the thermostat is designed to either recirculate the fluid through the block when cold or redirect it through the radiator when hot. this is done by either closing the outlet to the radiator and opening up the bypass port when cold, or closing the bypass and opening up the outlet to the radiator when hot. the thermostat has a rear seal at the bypass port to ensure it is sealed off when the thermostat is open to the radiator. if this seal is bad the water will continue to bypass the radiator and shortcut back to the engine. Item 33. part number 928-106-163-00.



Another possibility is the mechanically driven fan. over time the silicone fluid can leak out of the fan clutch and then the fan doesn't drive at full speed even when the clutch is hot. if the fan rotates very freely by hand (with engine off of course) then it is likely that the fluid has leaked out.. another way to tell is to have someone watch the fan when the warm engine is shut down. the fan should stop fairly quickly (about half a revolution as a ROUGH estimate). If this is the case, the fan clutch either needs to be replaced or have silicone fluid added (Here's a place to start. search rennlist if you need more info).

[PorscheCollecto]

Hi all,

THX alot for all the input, I really appreciate it.
I need all the input I can get, the problem is making me lose all my hair. (or least it feels like it)

I'll answer on your input now.

Regarding the rear seal (no 33 on diagram above), yes, I did exchange it. The old didn't look bad, but I still replaced it. I also when installing the thermostat insert it correctly. Also as it looks on the diagram above.
Is there anyway to test the new thermostat and the rear seal now with all assembled?


On the viscous fan, yes, there's a potential chance it's not working fully. When I test it at cold engine, I feel it has some resistance, but it still takes at least a full turn, perhaps even two, which I believe is too much. But when the engine is running the fan drives and I do feel it deliver airflow, but of course the good question is if it's enough. I'm concerning to replace it - but it's rather expense so would like to be 99,9% sure (if possible) before buying a new replacement.
Also heard I can rebuild it, but also see many complaining about after rebuild it only last for a few weeks/months. And that the new silicone oil is difficult to get. Don't know if these things are true?


Regarding if both radiator hoses are hot, well, in the begining the passagerside hose is hotter, alot hotter. Later the driver side gets hotter, but take time. I tried yesterday with IR-termometer to measure on the hoses. The passagerside hose rose to approx 150F before the other was at 85F (driverside) or some like that.
Is there a good way to identify if the coolant is circulating as it should?


Condition of the radiator is good, I would say. It's not new or anything, could actually be the original one, but looks fine. No bruises, no leaks, nothing idicates on the outside it would be bad. Of course could be different on the inside.
I've checked for debris, there's nothing there. There was a little, which I removed, but not enough to make a difference and after removing it, and testing no change.
The electrical fan in front of the A/C, I've now rigged to run all the time, fully speed (loud). I hope this would have help a little, but it make no difference really, I guess it's because the air only blows through the A/C first.


Really want to get out on the roads again, but don't like to drive it when it's so close to the red area after 10-12 min of engine running.
I hope to hear more from you guys - as I say - I need all the help I can get. :-)

Cheers
Chris

[Opelotus]

I think your next goal would be to verify actual coolant temperature, to make sure the gauge is actually reading correctly. Often times when the various connection points get dirty or corroded, the gauges will not indicate accurately. Inspect/clean the two terminals on the water temperature sender on the top of the water bridge and see if that makes a difference in the gauge reading. Also, see if you can measure coolant temperature with a thermometer placed in the coolant expansion tank. You may also be able to check the temperature of the water bridge with your IR thermometer.

[harborman]

Originally Posted by Opelotus

I think your next goal would be to verify actual coolant temperature, to make sure the gauge is actually reading correctly. Often times when the various connection points get dirty or corroded, the gauges will not indicate accurately. Inspect/clean the two terminals on the water temperature sender on the top of the water bridge and see if that makes a difference in the gauge reading. Also, see if you can measure coolant temperature with a thermometer placed in the coolant expansion tank. You may also be able to check the temperature of the water bridge with your IR thermometer.

I had mentioned that earlier. See if the engine temp is accurate. I hope he informs us of what he discovered.

[PorscheCollecto]

Hi again,

Yes, good point - makes good sense to test the coolant temperature. So I just did some meassurements and pictures. It's in celcius degrees on pictures. I started the car and left it in Idle for about 15-20 min before driving for 15 min approx. Then came back and toke these pictures.

Temperature gauge:
https://ibb.co/ZhQbhN2

Passageside hose:
https://ibb.co/GsjRtRz
83.0C or 181.4F


Driverside hose:
https://ibb.co/YNHGZ2y
50.3C or 122.5F


Coolant tank:
https://ibb.co/0sGLqPf
84.1C or 183.4F


Regulator housing (towards engine):
https://ibb.co/yVZGpHz
83.7C or 182.6F


Regulator housing (towards radiator):
https://ibb.co/Byt5j8b
61.3C or 142.3F


I also toke a drive in the car after a few minutes it was very close to the red area. But never went into the red area. And after more 5-10 min more driving it ended up at the same line as seen in the first picture of the temperature gauge. And it stays there.

BR
Chris

[Mrmerlin]

based on your testing and parts replaced the last thing that you have to do is replace the fan clutch Roger has nice aftermarket replacements for under 250.00 the factory part is over 1200.00 .
NOTE also replace the coolant cap and the heater control valve and short hose,Roger has nice Behr stainless caps as well

this should fix the hot running,
if that doesnt wqork then replace the head gaskets

[PorscheCollecto]

Hi Mrmerlin,

Thanks alot, I'll follow your guidance and invest in the fan clutch and install it.
Regarding the "heater control valve", could that do anything in relations to my overheating problem?
I would just assume it stayed open and gave problems with constant heat in the car?

Actually, now you mentioned it (heater control valve), I inspected it today from below (car was on lift), and I could see a drop of coolant from the bottom of the heater control valve, so something could indicate it's leaking slightly. A few drops I would say, nothing major, since there's no visible loss of coolant in the system (short term).
But again, could it be the culprit to the overheating problem?

Cheers
Chris

[harborman]

Yes, replace that heating valve and also the small hose connected to it. I don't think is causes a over heating problem however. As MrMerlin mentioned, maybe your fan clutch is faulty, so check it out.

[honerboys]

is 185-ish degrees really too hot for coolant? - could gauge just be off?

[harborman]

Originally Posted by honerboys

is 185-ish degrees really too hot for coolant? - could gauge just be off?

I think many cars run at 195, so 185 is reasonable or on the cool side I would think.

[PorscheCollecto]

It feels rather hot - the engine. I mean hotter than I would expect it should be. Eg the cross-member in the engine room is so hot I can hold my hand on it.
But that's just my judgement.
But to rule it out - do anyone know how to "prove" that either the temperature sensor or temperature gauge is faulty?

Ps: I've tried to create a seperat thread to get the resistance values for the temperature sensor.

[honerboys]

since the gauge does not have actual degree markings it would just be a guess as to what the lines really represent - has anyone ever tried to figure what lines are what temp?

[harborman]

Originally Posted by PorscheCollecto

It feels rather hot - the engine. I mean hotter than I would expect it should be. Eg the cross-member in the engine room is so hot I can hold my hand on it.
But that's just my judgement.
But to rule it out - do anyone know how to "prove" that either the temperature sensor or temperature gauge is faulty?

Ps: I've tried to create a seperat thread to get the resistance values for the temperature sensor.

How about taking a temp reading with one of the infrared gauges. Or take it to a shop that can do it. You can't rely on the car gauge except for approximate reading. I bet Harbor freight has the gauge. About $25. https://www.harborfreight.com/121-infrared-laser-thermometer-63985.html

[PorscheCollecto]

Originally Posted by harborman

How about taking a temp reading with one of the infrared gauges. Or take it to a shop that can do it. You can't rely on the car gauge except for approximate reading. I bet Harbor freight has the gauge. About $25. https://www.harborfreight.com/121-infrared-laser-thermometer-63985.html

Hi Harborman,

Already did that - used an IR thermometer - if you look higher up in thread. I also added links to pictures.
Issue is that perhaps it’s not too hot after all, but the for sure the gauge showing wrong value. It’s at lady white lines always and will go up to the first redline, never over. But a 928 isn’t suppose to be that high. So if the car isn’t running hot, the gauge or temperature sensor wrong. This would be nice to verify, so I can fix the problem. :-)

[harborman]

Originally Posted by PorscheCollecto

Hi Harborman,

Already did that - used an IR thermometer - if you look higher up in thread. I also added links to pictures.
Issue is that perhaps it’s not too hot after all, but the for sure the gauge showing wrong value. It’s at lady white lines always and will go up to the first redline, never over. But a 928 isn’t suppose to be that high. So if the car isn’t running hot, the gauge or temperature sensor wrong. This would be nice to verify, so I can fix the problem. :-)

Sounds like the gauge or temp sensor. Also, possibly bad connection. These cars are old so could be some resistance in the connections.

[Crenshaw77]

You don't know for sure what the engine temp is?