Hi,
I live in North Dakota where it is very cold, My 98 A6s coolant temp will not move above C, even after driving for 1 1/2 hour on the highway. Weird thing is that if I shut off the car and then turn it back on the temp goes up like a quarter and they moves back down once I start driving. Is this a stuck open thermostat or some temp sensor? I do have a vag-com. If there is any way to use that to troubleshoot please let me know.

Thanks!
And a Happy New Year to All...

 

Sounds like temp sender, it's pretty easy swap on most engines. What engine do you have fitted?

 

98 is going to be the early 30v 2.8. And to change the temp sensor on a 2.8 is a PITA. Not hard per say, but very difficult to get to with man hands.

If that doesn't solve your problem then start looking into the thermostat. And if it turns out to be so, change the timing belt with it because you will be right there.

 

Thanks for the update guys. Yes I have the 30v 2.8. Been doing some searches online. I know there is a sensor behind the intake. Is that the only one I should try swapping or are there other sensors. Some have a green one and some have a blue one. Is there away to find out what I might have before pulling things apart, so I can buy the right sensor. And is there a way to check the sensor with the vag-com.

 

Agree. Forgot you only got limited engines in USA, in UK it could have been 1.9tdi,1.8t, 2.4 or 2.8 so it's a bit harder to guess!

 

My temp sensor on my 04, A6 did nearly the same thing. Sometimes it wouldn't work, sometimes it did, but it would go back down to cold. Brought the car to the used dealer I got it from because it is still under warranty.. They replaced the temp sensor, all seems to be better now. (Knock on wood) good luck!

 

is it ok to drive the car with a bad temp sensor. its very cold here and i was thinking about waiting till it get a little warmer to change it.

 

The blue one has a square connector.
The green one has more of an oval shape to it (kinda flat on one end.. round on the other end)
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I'd try to get it done soon. ECU thinking the car is cold = burning more fuel and not running as efficiently as it could.

Also, I'm not sure the thermostat should be ruled out just yet - If it consistently stays on C (and never straying from those symptoms) .. it's possible that it could be stuck open.

Cold Air + Highway Speeds with a Thermostat stuck open = it's not going to warm up until you stop, and leave the car idling for a while. The temperature rising after shutdown/restart could be heat-soak from the hot motor (don't quote me on this).

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But considering how flaky the temp sensors are on the C5 platform, definitely start there. Hopefully that fixes the issue, if it doesn't.. then it's going to get a LOT more involved.

 

thank u for the response. I guess Ill try to change it sooner. I was thinking of the thermostat too but i guess ill start with the sensor ans see what happens.