ok here is my issue. my 2001 a4 quatro just started over heating and so i replaced the thermostat. that didn't help. so then i replaced the coolant temp sensor that also didn't help. what could this be caused by? also when i changed the thermostat i noticed when i took the throttle body off i noticed that there is oil in the intake hose i'm guessing that is not good. please help.

 

wish I knew enough to help on this issue.
Have you had a chance to scan for codes? Did you find anything? Engine codes (even if the CEL is not lit) might give some clues.

 

If it's a 1.8T, you maybe have a bad water pump. The plastic propeller breaks and so the shaft just spins connected to nothing. Happened on mine.. i replaced with a new water pump with metal propeller while i did the timing belt and tensionner.

 

water pump, coolant having leaked out, or a clog in the cooling system. Or if it only happens at idle/low speed then possibly fan-related (fan, relay, fan belt, etc.)

 

are you using g12 coolent?

 

what dragon said, or its pretty unusual but sometimes t-stats are defective when they come. I ALWAYS check them prior to installing by boiling some water and dropping them in to make sure they open. Takes an extra five minutes, but can save you a headache...

 

2nd the water pump problem! Just replaced mine a month ago.

Just make sure you completely "burb" the system when you're done putting the new coolant in. Otherwise You'll have no heat. That ALSO happened to me

 

after i replaced my water pump i started it up and it was overheating but my dad turned the heater on to max and the coolant level went down cuz the air bubble got out i added more coolant and was good to go no more overheating.

 

Yes I am using g12. Does the metal waterpump come with certian years or was this developed after the b5? Also someone not from this forum mention to me that it could be a head gasket is this a possiblity. At the current time in not wanting to drive her and I don't have any codes but I'm triing to get a obd II reader so that I can pull some codes. Thanks to all of you that responded. Also I noticed that when it does over heat the coolant in the overflow tank appears to be boiling.

 

did you replace the coolant recently? looks like you have an air bubble and thats why it looks like it is boiling. try opening the cap of the coolant tank and turn the car on, also turn the heater on to max. it should let all the bubbles out if not i have no idea what is going on