New here and have checked all the previous coolant threads but didnt find my specific problem. As of last week I have a 98 A4 2.8. As long as I'm driving with the engine revs at around 2k or better my heat operates normally. I'm new to Audi but in previous vehicles my issue was usually a sign of low coolant. But the coolant is full and appears clean as does the overflow tank. It takes what seems to be to me a long time for the engine to reach operating temperature, about 10 minutes when idling and about 5 to 7 miles when driving. Takes at least 2 to three miles of driving before any heat at all comes out of the vent and probably at least ten miles of high revving operation before the heater blows as hot as I think it should. I'm thinking my thermostat is stuck open. But before I go digging into that I would like to hear any thoughts or opinions from you experienced Audi owners.

Thanks

 

Thermostat is a good guess from me!

 

Sounds more like air in the system or a blockage in the heater core. No heat at idle is the opposite of what you'd see with an open t-stat. If its open, you'll have heat at idle and will lose it while driving. When you get none at idle and have heat while driving its typically air or heater core.

 

Ok since the first post i have flushed the heater core and it appears to be clog free. Found a receipt in the glove box for a new thermostat and water pump, called the P/O and he claims yes he installed them two years ago. So thanks to your replies I'm thinking maybe the "air in the system" idea. I have not had this issue before on any auto I have had, if anyone has experience in this please post. Ill do a search for the procedure but would still like to hear from you audi guys.