audi 4k engine cooling / interior heating issues

[tom winter]

Kevin - take a very close look at the overflow tank. I had a similar problem
in an '86 4000 that I used to own. The culprit was a hairline crack in the
tank. Once I replaced the tank, it held fluid and my problems went away (the
crack was small and the leak was hidden from view, so it took me awhile to
figure out where my coolant was going).

The tank is easily removed, replaced (20 minutes work time, max). I used one
from a junkyard that was intact. cost was $15.

HTH

Tom W