97 A4 V6 keeps overheating...HELP!!
 

Hi everyone. I have a 97 A4 that overheats after running for about 10 minutes. I was told it was the fan switch so I changed it. Also changed the tstat, and water pump...not fun by the way..

Anyhow, it still overheats and not sure why. Any help would be appreciated. I didnt think 10 minutes was even enough time for it to overheat.

ac works, both fans come on. coolant isnt brown.

I just filled and drained the coolant a bunch of times with water and ran it and drained it again and its coming out clear but it doesnt seem to be getting hot. The reservoir seems cool still and the top hose. The bottom hose isnt that hot either.

Also when it says its overheating and i shut off the motor and crack the reservoir cap there seems to be a back siphon of water into the reservoir. Is this normal?

The coolant coming into the reservoir when you unseal the system is normal. If the lower hose isn't hot, then there's a blockage. Typically it's the thermostat, and new ones out of the box have been known to be bad. It could also be the radiator - get the car warmed up and try to feel the face of the radiator - it should be uniformly hot. If there is a cool spot, you have a blockage. Also, in 10 minutes' time from a cold start, the thermostat likely won't open if it's only been sitting and idling. Is the engine truly hot or is the gauge only saying it is? The coolant temp sensors are a known issue and fail - you may be seeing just a bad reading from it. Last immediate idea is a bad fan clutch. The fan spins all the time but is only driven hard when the clutch engages at temperature. If it's not engaging, you may be heating up because of that.

+1 on the thermostat. An infrared thermometer can be useful for diagnosing overheating issues because you can see that different parts of the engine are at drastically temps.

Does it "smell" hot when it overheats? Every engine I've worked on has a very distinct smell when it gets too hot. If it's just the gauge needle pointing to the HOT zone, but the engine doesn't seem hot or smell funny, try replacing the coolant temp sensor as suggested before. It's on the passenger side near the throttle body. Not real hard to do.

Engine doesnt smell or get hot. I can hold my hand on the top of the motor, and both coolant lines without having it hurt and it says the car is overheating. I will try the coolant temp sensor tomorrow.

any surefire way to test fan clutch. Mine does not overheat really, except if I am in standstill traffic and it has been runnign a while. I only noticed this the last two weeks after also starting to hear a whirring or whining noise coming from front of angine in fan area that is engine speed related.

Back again. Need more help. I bought the coolant temp sensor but its round and mine is square with 4 big pins. I had autozone pull up different types, years, and some makes and none match even jetta, not sure what to do.

They screwed up the way every store screws up. They gave you the one that goes into the side of the radiator, not the ENGINE coolant temp sensor. Tell them to look it up as the engine coolant sensor.

So I changed the coolant temp sensor today and it made the needle move a littl slower but still overheats. I let it run a while this time and i can get the ac to crank but the heat never gets hot??? Also the top hose on the reservoir gets hot but the bottom one was still cold...still confused.