We have been having troubles with our Audi 90. The car has been serviced at least once a year for its entire life and just recently was serviced again.Just prior to this thetemperature warning light came on after awhile of driving. Thenafter the service as soon as the carwas started the light was on. After a few minutes of driving the engine is overwhelmingly hot, even in the rain. The levels of fluid are fine. We took it to get 'fixed' and were told there was nothing wrong. We investigate ourselves and found that the fan was not starting. We took it back and told them that we thought they were related. We were told that the car over 100 degrees (on the guage) with very hot coolant was normal for the car. It wasn't like that when we got it though.It was never hot.
Now when we have the car stationary it overheats and cools slightly to 85 degrees on the highway (the light still on) Does anyone have any ideas what is wrong? Oh, the mechanic said that the fan comes on when the temperature is over 100 degrees (celcius)

Any additional help would also be appreciated by email. (I'm in Australia)
kyana_assassin@yahoo.com.au

 

well firstly 100C isnt actually overheating and sounds the norm, although typical culprtis would be the ECT sensor sending false reading, thermostat sticking or the coolant level sender being bad, i would in this order try this replace the coolant level sender, replace the ECT ( these 2 are relativley cheap part) than if all else fails check to see if the thermostat is working but taking it out and putting in a pot of boiling water if it opens up measure the tempreture and need be repalce with a new one.

 

when you did your last service did they back-flush teh coolant system? if not, try that before spending on replacement parts. always try teh cheapest solution, first, then work your way up the cost-scale. Most times you'll hit on teh solution before spending BIG for something small.

 

Thanks for all of that. Here is an update: Had it checked again. Once again nothing wrong. Drove it home. Red light on. Then now every second drive it is off then on etc. The mechanic said that the guage could be wrong so its normal temperature before of 60 degrees now reads as 100. (It is such a relief if 100 degrees is normal and the guage is correct) We don't know if the coolant system was back-flushed. I guess things are touch-and-go.

 

The coolant temperatute sender (not the ECS) could get wrong by the age or mostly by engine wash (happened to me on 4kq).
Verify the engine (coolant) temperature by measuring with external tool.
The fan should be on at 93C. The fan Thermo switch should be at the bottom of the radiator, not complicated to replace.
Look for proper flow from the radiator to the expansion tank (I had a plugged hose in the past)The worning light gets on by the fluid level (on turns).

 

is there heat in the cabin? does the cooling fans come on when pressure builds up? when was the water pump changed?
all symptoms could lead to a failed water pump and coolant wouldn't be pushed round the engine then it would overheat or show this symptom,
are all the components working is the question?