Hi, Audi A6 1.8T. Fitted with standard viscous-coupled fan and electric fan. All completely normal at town speeds. At high speed, the coolant temp falls to the bottom of the guage. After a bit of experimentation this turns out to be engine speed related. Anything above 3800rpm for any length of time and the temp falls rapidly. Reduce engine speed for a few minutes and all returns to normal. Thermostat changed with no improvement.
Could it be viscous fan, temperature sender, weird electrical snag? Any thoughts please.
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Is the temperature of the water actually dropping? you can check by putting your heater on full, see if the temperature is lower than normal, or by stopping and feeling the temperature of the engine and radiator. If the engine is cooler than normal and the radiator warm - you have a duff thermostat.
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Check the fan will rotate by hand and is is not seized. Does the engine warm up as normal in a sensible time. Check the connections or the temp sensor for corrosion. This may still be a sensor problem if all else checks out. Not an uncommon fault. Regards Peter
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Thanks for the replies. The heater seems to work normally, the fan rotates freely and I've already replaced the thermostat. I'm leaning towards a sensor problem, although it just seems unusual that it's so predictably engine speed related.
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Is the viscous fan working properly? Ie fast when cold and slow or off when warm?
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ac
Should that not be the other way round? When the fan is turned by hand (Engine off of course!) the viscous coupling should be stiff on a hot engine, but free on a cold one. That said, I doubt this problem is fan related. Generations of cars maintained engine temperature with continuously driven fans before viscous coupling fans were introduced.
JS
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Probably you are just getting a false reading then. Sounds like an electronic fault, unless the sensor is faulty being cooled by the draught at high speed.
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Intriguing one this ... my first guess would be thermostat, but we've already been there, unless the replacement is also faulty.
Has it always done this?
Is it definatley related to engine rpm, not road speed?
wrong water pump, giving too much flow? OK that's 100,000:1 ...
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The temp sensor is a common problem as your dealer will dell you when to purchase a new one. Regards Peter
Edited by Peter D on 09/07/2008 at 15:37
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Thanks for all your thoughts. It is definitely engine speed related and not road speed. In 3rd, 4th or 5th gear it happens at about 3800rpm. It's a fairly recent problem, the car having been brilliantly reliable for nearly 100,000 miles.
I'm going to change the sensor next as it seems the most likely culprit. Just don't see why it should be linked to a certain engine speed. I'll let you know if it works.
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Thanks for all your thoughts. It is definitely engine speed related and not road speed.
Did you sove the problem, I have the same problem :)
Edited by Dynamic Dave on 30/09/2008 at 13:32
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