Thanks everyone with the help on the timing belt/water pump procedure. My car appears to be running ok with the new belt.

However, now I'm frustrated with the overheat warning sensor -- it comes on after 5-10 mins of average driving.

The water temp guage appears to be working as it always has (looks as if the car runs cool) -- I've never seen the guage go above the middle. The fans appear to be running ok, they both come on after a while (they don't stay on after the car is turned off though). I attempted to 'burp' any bubbles out by removing the coolant cap and squeezing the lower rad hose, but not sure how well I did (or if that has anything to do with it).

I drove at least 20 mins with the light on and the car doesn't FEEL or smell like it's overheating, the intake manifold is not cool, but I can put my hand on it without burning.

Anybody have some basic troubleshooting ideas to see if I can isolate?

Thanks in advance.

 

Doug,
I think you mean the warning light for cooling water level!
Check the cooling water level and if this is ok, then check the two sensors - One for level and one for pressure
Most properly the problems is due to a faulty pressure sensor
Also see:
https://rennlist.com/forums/showthre...ressure+sensor
Regards from Erik in Denmark

 

Erik,

Thanks much for the reply.

The light I'm talking about is at the upper band of the coolant temperature gauge, similiar to how the low fuel light is at the lower band of the fuel level indicator... In the owner's manual, it's referred to as the Coolant Temperature Warning Light.

 

Doug,
There's another possibility, and that is air still locked in the cooling system after the water pump job: the 928 is frequently a proper PITA to get a complete air bleed on. There are two thermal sensors in the top of the thermostat housing - if the one driving the temp gauge is in air...
To bleed the air, back out the thermal sensor on a warm engine to check/allow for air to escape. Once all air is out, the upper/lower rad hoses will be 'hard' at operating temps.

 

Thanks Garth, This sounds like a good avenue to check! I'll check it out this evening. [he says crossing his fingers]

 

Doug, i have exactly the same problem with my car... it bugs the sh*t out of me!!! unfortunately i have the 928S Euro Manual, so the thermal sensor is right down under the oil filler/various hoses, copper pipes of some description, etc... let me know how you get on, as i'd love that light to go out permanently..

 

I'll definitely report back Gareth.

 

Garth,

I did what you suggested and backed off the thermal sensor on the thermostat housing just enough for some fluid to seem through to make sure there was no more air. It was pretty late so I didn't get a chance to test drive, but I revved it pretty long and hard and NO INDICATOR!!

I'm impressed with your kung fu. It appears to have fixed it! Thanks for the suggestion.

I'm curious though, I don't get those sensors... I grounded each of those sensors and it made the coolant temperature gauge shoot to the top (and make the indicator light come on. If the sensors are right there next to each other, why was the warning indicator illuminating and the temperature gauge stay low at the same time? Do they not work the same?

Thanks again everyone!

 

well that sounds like good news.. let me know how you get on today, Doug..

G

 

Well, damn. Halfway to work I'm thinking it's licked, but then the lamp comes on again. Maybe it's more air bubbles? I'll try backing off the thermal sensor again this evening...

I know this will sound stupid, but I wish I could just eliminate the possibility that I am in fact overheating... If I ground the thermal sensors the gauge goes to the top so I think the gauge is working. The fans work. The water pump appears to be moving water because I see turbulence in the coolant resevoir when revving during the burping exercise. What else could I check to make sure I'm not really overheating?

 

If you have the WSM, chapter 90 lays out the steps to check out the Central Warning Unit (CWU) - the red lamp in the temp gauge you are referring to is driven by the lead with the narrow female spade on the coolant temp sensor: It's sounding more like an electrical glitch in the wiring or CWU, for it sounds from your last note as if the temp gauge is operating through it's normal range.
Since the behavior of this warning light changed (somewhat) after last night's exercise in playing with the leads, I'd first look at the connection and wire for breaks/corrosion.
On the coolant side, sounds like you've done a thorough job bleeding the system; as far as coolant circulating correctly - if the thermostat was out, the two seals have to be in and in the correct order: lastly, the majority of times I've seen a thermostat stick is after letting it dry out (not that there is a choice) when doing a water pump etc. - consquently, started taking this as an opportunity to install a new unit.

 

Perx,
I am not familiar with the S4 instruments, but it seams you have a normal cooling water instrument plus a warning lamp. As your your manual said:
-------------
quote:
Needle in upper field – warning
If needle enters the upper field, the engine is overheating. The central warning light will also come on. ..............
quote over
--------------
Is the instrument in the upper field?
If yes, look for a general cooling problem
If now, check the cooling water temperature with an external temperature instrument (infrared) and find out which of them are wrong.
Most properly the signal for bouth comes from the same sensor (Check in el-diagram)
Good look with your search

 

Lamp went on on the way home from work again... nothing new.

I tried backing off the thermal sensor unit, but that didn't have any effect.

I borrowed an infrared temp gauge to validate temperature. When the lamp is illuminated after running for 20-30 minutes, the temp of the thermostat housing is approx 55C and the lower rad hose is approx 75C. I don't think it's overheating.

I'm discouraged... Should I start troubleshooting the sensor, wiring?

 

I haven't really made much progress on this yet. I was thinking of replacing the sensor for the hell of it. But... Get this...

I was getting tired of seeing the light while going to and from work, so I unplugged the smaller spade wire from the thermal sensor (the one I though controlled the warning lamp), but the light still came on while I was going to work.

I think I'm looking at an electrical problem, not a thermal switch problem. Anyone agree? Any ideas on what to check next? Central warning system?

 

The coolant warning light can also be indicating a problem with the cooling fans and or front flaps . It gets a signal not only from the temperature sender but also the fan control circuit . So with the temperature sender unplugged it probably is alerting you that the fan control system is having some issues . There are pages and pages in the repair manuals about how the cooling / fan / flap / speed control / brain function .