My audi a6 keeps overheating at leat thats what the gauge tells me. It only happens when you are doing 40 or more . When you free wheel the temp shoots back down rapid. Any ideas

I would check the thermostat first. Remove the thermostat and place it in a pan of water on the stove. Place a thermometer in the water with the thermostat and slowly increase the temperature until you have reached 194 degrees Fahrenheit or 90 degrees Celsius. Watch closely for the thermostat to open slightly. If it opens then the thermostat is good. If it does not open, replace it. Try that first and see what you come up with.

if the temp gauge does not return to zero with cold engine then the problem is going to be a gauge/instrument pack fault

Thermostat might be stuck.

Sound like either the Thermometer Housing, Thermometer or water pump may be in trouble.

If no leaks you can rule out the Thermometer Housing.
But regardless you will need to replace all three if any one is bad.
And the timing Belt while you are in there,
Only because it a 5 hour Minimum Labor job to replace either of them.
And there all right near one another,

A real pain to get to those. Thank you Audi...

Selvol

Hi there:the Audi manual never talks about a 2 stage aux fan just that the aux fan runs with ac on and it can run with out ac on if there is an overheat issue on the coolant side where as the a4 info clearly states a 2 stage aux fan system that would lead me to think the early 4.2 did not use a 2 stage system. Your car is not overheating and boiling over out of the coolant tank it is showing a little hotter than what would be perfect but it is still in what Audi calls acceptable range. The whole coolant system is new I would start looking at your sensor and gage systems there is a coolant sensor in the rad but that is most likely new if they replaced the rad. The gage uses a temp sensor on the engine for the gage I would replace that sensor and test the gage with a resistance input tool we have at the dealer. Could be a gouge or the wiring to it. There is a coolant fan module that could be defective if your sure there was a two speeds to the aux fan.




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Here it is...Hope this is some help to you ??

THIS IS AS IT SHOULD BE,the temp should rise after about 1 to 2 miles,VW group engines have very little water in them compared to some other makes and should get to "operating temp" far quicker than most other cars.as long as your not overheating/overcooling,your gas mileage will be at its optimum.

overheating where is the thermostat housing located

in the back of the engine , below intake boot , closer to the pass. side of engine.
seats on top of plastic water flange outlet.
very hard to get. 4 wire sensor.

can anyone tell me where the fuel filter is located on the 2001 audi A-6