temp gauge, irregular/inconsistent
 

audi a4 1,8 ts quattro

previously my temp gauge used to stabilise around and stay in a narrow spectrum around 90 C, (the middle) now it tends to stay around 80 C sometimes even slightly lower and only rarely reach 90, is this a sign of busted thermostat or other malfunction that I need to deal with?

thanks
/
David
Sweden

check the coolant temp sensor, thats usually a culprit on b5 audis

Okay thanks, should I just replace it or is there a good way to determine that it is broken before replacing ?

Thanks

just replace it. its like 15 bucks and causes too many problems.

okay, thing is when I turn the engine on after having had it turned of for a while it will display 90 C and will continue to do so for a while, and then it will back down again as if it was cooling too effectively. So maybe it is showing the correct temperature but something else is wrong?

thanks

It wouldn't go down if it sat, it would go uP a little. The sensor can cause bad readings if it's bad. What have you done to troubleshoot so far?

Replace the damn thing lol

Among the weird readouts, and yes it should go up a little if you turn the car off, come back a little while later and turn it back on., but it will also kill your gas mileage because it is tied into the engines warm up process. It will add more fuel to each cylinder thinking the engine needs to warm up still. It will also cause a rough idle.

Replace the damn thing haha

haven't done very much yet, was thinking at first that the thermostat was the culprit, I'll start with the sensor as suggested and do the thermostat if that doesn't do it. thanks both of you for helping :)

noticed funny thing today, for some reason if I change settings on the climate control, for example engage ac and change temperature the temp gauge will soon start to display 90 C as it should, after a while it will go back down to 80 C, then if I change back again and wait for a while I can repeat this process to get it to show 90 C, anyone recognize this weird behavior ?

How big of a job is it to replace the temp sensor? My gauge readings recently tends to go up after turning the car off but quickly goes back down after re-starting the engine for a few minutes.

P.S I thought the electric fan should stay on if the car is turned off while it's running ?!?!? Is that also a sign of a bad sensor?