I have a 98 a4 2.8 quattro. last week it started running hot, at 105 - 110 on the guage instead of 90. today i checked under the hood and noticed the upper rad hose is hot, but the lower hose is cold at operating temp. I am thinking it is a stuck closed thermostat but not sure. never owned an audi b4 and only had this one for 2 months. any ideas? a friend suggested the water pump but if it was toast the car would overheat right away and bury the guage right?

 

try a thermastat. I hate to say that cus its a bitch to get to. and be sure to fill the coolant back with the correct stuff to.

 

Before you start taking the thermostat out that is located behind the timing belt I would plug in diagnostics and run final control on the analog dial this is where I would expect the fault to be if not check the temp reading from the temp sender in dah pannel measured block values and in engine measured block values at the same time move the wires about on top of the temp sender to see if this causes any fluctation in the temp meaning that you need new conectors at the plug (all though if the temp sender is nakerd it will cause a fluctaion doing this any way so replace it first and then re-check).
The temprature diffrance that you are talking about is quite normal this is because the a raditor cools the coolant down, it also has a viscos fan so the fan is constantly cooling the raditor/coolant which works relay effectivly. A sign for a failed water pump on stright four engine is that the coolant isn't pumping out of the small coolant return on the coolant bottle but this isn't so on the V6 engine only drabs return.

If you don't know somone with the diagnostics who know how to use it properly your best off going to the audi centre otherwise you'll be paying for things that you don't need.

Audi scientist