Can I call on your collective wisdom and expertise guys? The radiator crapped out on my 1998 A4 2.4 earlier this week. I have just changed it out, refilled the cooling system (no leaks) and started to bleed it up. After about half an hour I am still not getting hot air through the heater vents, but there is no more air coming out of the expansion tank and it is not overheating. I put the cap back on and took it for a spin as this sometimes helps. The scary thing is, the higher the revs get, the warmer the air gets, but as soon as the revs die down the air gets cool again. I have my suspicions as to the problem, but want to see what you guys think. I'll keep my theory to myself for now to reduce the chances of looking daft! lol. All input gratefully accepted. Thanks everyone.