reno928s

Ernest, Is it possible that the belt is not properly seated on the waterpump idler or pulley and is slipping at highway speeds. Did you replace all the idlers when you did your timing belt? My girlfriend will have my head if she sees me, oops too late, got to go. Reno

ErnestSw

Reno,
What you're basically asking is whether the belt is loose enough that it's not turning the water pump. If it were that loose I'd have a lot more problems than running hot.

Erik - Denmark

Ernest,
Dieter from Germany asked me to place this answer - he is not a Rennlist member but active on http://www.pff-online.de/
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Hello Erik,
because I´m not a member of the Rennlist I would ask you about suggesting to change or decalcify the cooler (only and carefully) in the Rennlist for solving the Overheating-Problem.
Certainly only if you thinking this could solve this problem.
Thank you.
Best regards.
Dieter (ds)

My latest posting at PFF:
Der 928 sollte bei 40°C Außentemperatur und zügiger Fahrweise noch keine Schwächen zeigen.

Ich denke, dass auch hier ein neuer Kühler das Problem beseitigen würde. Nach 10 bis 15 Jahren und ungefähr 4-5 Wasserwechseln dürfte sich schon etwas Kalk abgesetzt haben und damit die Kühlwirkung verschlechtern.

Entkalker greifen Dichtungen und unedle Metalle an (z.B. Aluminium und Kupfer). Darum würde ich höchstens versuchen den ausgebauten Kühler etwas mit Essig und dann mit Wasser zu spülen. Ob das zum Erfolg führt ist ungewiss.

ErnestSw

Hi Erik,
Thanks for the message. I have replaced the radiator and it has not helped.
Ernie

Earl Gillstrom

Ernest,

You probably already checked this, but are you sure that the fans are running full speed? One easy way to check is to remove one of the wires on the "pressure switch frigen". That is the switch on the top of the pipe next to the AC receiver drier. With the AC on and the ambient temp low (75F), if I remove a wire, on my '91 GT, the fans run considerably faster.

ErnestSw

Earl,
I THINK the fans run at top speed when the AC is set to recirculate. It's not acting like an air flow problem.

Earl Gillstrom

Ernest,

I tested in recirculate and the fans sped up when I removed a wire form the "frigen switch".

Fastest928

is the water pump flowing water?

Is the rad cold and the engine hot? Check that the 100C or there about is at the inlet, outlet and in the rad core....

If the temps are not within 20 degrees, the water pump impeller is failing and thus, the pump has failed.

Our race engine runs at about 185 at the head crossover, but the temp gauge always reads about 200-205 (cycling between the thermostat opening/closing)

marc
DEVEK

ErnestSw

Marc,
My last reading at the crossover was 219 by an infra red thermometer. The top hose read 215, but the thermostat housing read 190. My cam covers always read in the 215-220 range.
No matter what I do the car seems to develop the same temperature equilibrium. I've affected the slope of the curve by installing the Devek radiator and blocking the rear channel flow, but not its end point.
Any suggestions would be welcomed.

Drewster67

I thought I would at least try to throw some ideas your way. Please excuse the items if already discussed.

1. Control Unit
2. Pressure Sender Frigen
3. Engine Fan
4. Output Stage
5. Flap Positioning Motor
6. Tempe Sender, cooling water
7. Engine Compartment Lid Switch
8. Temp Switch

For Troubleshooting the manual goes on to say ...and as well as testing the above items -

Test the Control Unit - Voltage Supply
Function Test of A/C Button and slide switch

I have a question regarding the Heater. (I quickly went through the manual but came up short.) Do the later sharks run heater cores?. I remember a few years back, my 5.0 GT Pony had an OH problem and it turned out to be a plugged Heater Core?. If they do, could this be the issue w/your GT?.

Hope this helps - Good Luck

Don.

Ok, it appears that you've got good coolant flow. The only thing you haven't investigated is whether you have a blocked passage somewhere, and I don't know an easy way to check that.

You've mentioned previously that you're getting pinging even with the stock chips. Perhaps this is the source of your problem? I think since chasing the coolant flow issue hasn't solved your problem, perhaps you need to fix your pinging issue. If you're getting pinging at operating temp, perhaps you're running too lean. Is your mixture set right? Have you checked for false air sources? Could you check the voltage on your O2 sensor after warm up? Both at idle and at 2500 rpm?

You mentioned that you have newly cleaned fuel injectors, so that's probably not the problem. Are you getting good fuel pressure?

My car has an "octane loop", which makes it easy to retard the ignition by 3 degrees - I don't think you have this. Is there any way on your car to retard ignition 5-10 degrees to see if that keeps the engine from pinging? Hey wait, you have knock sensors. Are your knock sensors working?

-Don

DG84S

Ernest,
It may be worthwhile to splice a length of clear PVC pipe into an old upper radiator hose and mount it just to confirm that coolant flow increases in proportion to engine speed. This would rule out internal blockage or a slipping water pump impeller. The clear PVC ought to be available through a swimming pool supply store (like Leslie's in Arlington,TX). I don't know how PVC will hold up under heat and pressure, so be careful!
Dave Goyne

ErnestSw

Hi Dave,
My "visible burping procedure" accomplished the same thing. When I put a clear tube on the radiator return fitting and strung it over the open hood of the car it was evident that there was a very significant increase in flow when I revved the engine. Of course, it doesn't quantify the increase.

Gregg K

Hi Ernest,
I'm sure you wouldn't have gone this far without noting this, but could the temp guage or the pc board it's connected to be part, if not all, of the problem? I'm pretty sure you actually checked the fluid temp. independent of the guage. But, you know, I think about you sometimes while driving down the road, and that one just popped into my head. That wouldn't explain the pining, tho.

Jim bailey - 928 International

Ernest ... you might find this interesting ........Porsche for the 1992 GTS modified the cylinder heads " To achieve better
cooling of the walls adjacent to the combustion chamber as well as the
exhaust ports in the cylinder heads , coolant flow both in longitudinal and
in transverse direction was improved . To achieve a modified direction of
flow , additional passages were incorporated . ( four small holes near the
exhaust ports ) . You have to ask yourself "What was Porsche trying to fix?
" Something made them decide to try to cool down the heads . I would
speculate that it was a detonation issue brought on by the 10.4 compression
ratio otherwise it was very late in the production cycle to be redesigning
the heads .... But only Porsche knows for sure why they did it and they are
not talking .