I bought a 96 A4 2.8 today with 118,000 miles. The coolant resovoir was just replaced by the previous owner. After purchasing and driving about 20 miles the temp needle started rising it got to about 3/4 so I pulled over and popped the hood. Both cooling fans are on, ran the heater and it cooled down. Also let the car sit then opened the resovoir cap to see if it would "burp" Drove the car another 20 miles on the freeway and it stayed normal. When I came to a stoplight it started to rise again but never passed 3/4, although I could smell coolant. Could someone PLEASE help me to get the temp to sit perfect always, I love this car! Is it most likely the thermostat? Water pump? Has anyone else experienced this issue and what resolved it? Thanks for your help.

 

It could be the temperature sensor.

 

What color is your coolant?

 

If the resevoir was JUST replaced before you bought it, there could be an air bubble in the system. There are a couple ways to bleed the air out, but my favorite technique is to take the cap off the resevoir (with engine cold, heat on) start it up and rev it up a bunch of times. Dont hold the revs, just put the pedal to the metal for a quick sec till rpms raise to about 3/4k rpms and let off and repeat. The air should make its way through the system and out the resevoir. Bad temp sensors dont cause over heating. So its either air in the system, or a sticky thermostat.