Hi fellow Audi masochists
Got a 2001 2.7bi-turbo allroad. At tickover speed heater blows cold or cooler yet above 2000rpm it blows hotter (but still not real hot)
Car had new stat before I bought it and engine temp gets up to normal nice and quick and stays there.
When I removed the hose which covers the bleed hole in the heater pipe hardly any coolant came out of heater. Expansion bottle is up to correct level and I've run it with cap off. Only way to get coolant to come out of bleed hole is unscrew exp bottle and raise it 6-8 inches. Did this, refitted hose as coolant poured out of bleed hole, topped up system but still same effect. Seems like heater has air blockage but how to displace it? I've worked in vehicle heating/cooling for over 30 years but this is baffling me. Read some old post on a forum that this could somehow relate to low vacuum pressure. I think there are issues with the car in this area (another job to sort) but how would this affect heater flow? Are there valves in the heater circuit that could block flow.
Sorry for long post but it's bloody freezing sitting at traffic lights just now!!
Jeff – in sub-zero Glasgow

 

if you had air in the system it seems like it would be effecting the cooling for the rest of the car. have you done a flow test on the heater core? it makes sense that it would cool down as you pick up in rpms since the coolant cools through the radiator, are you sure that its properly getting up to temp? have you touched the radiator hoses to verify that they're hot? also feel the radiator hoses going into the heater core. if its cool then you have some other problem, but the valve that controls flow into the heater core could be faulty as well and not letting enough coolant into the heater core, thus not producing much heat.

 

Thanks for reply. The problem is definately air in heater. Rest of system works fine but I discovered damp around the metal part of a coolant hose that connects to the turbo. The coolant hoses that connect to turbos are metal close to the turbos and they are crimped around rubber hose that then runs across the back of the engine. This hose is perished and I have had to put in a repair piece. However I noticed the metal hose where it crimps round the hose is damp so my theory is this. Car gets hot and up to temperature and hoses are pressurised and so rubber hose seals against inside of metal crimped part so no loss of coolant or drips. When warm I can bleed air out of system and heater works great. I have rigged a proper bleed valve in to heater pipe so its easy to bleed. However, when car cools, pressure in system naturally drops and then the rubber hose contracts and allows air to be drawn in to system. Start the car next day and its full of air again. I have managed to improve things by running some sealer in to recess round metal part of pipe.
Alas, car is up for sale - too much expense already and I can see more to come!!

 

Great! Glad you got it figured out! Yeah I've had mine for 2 months and I'm just trying to fix it enough to sell it!