Hi all, got a 97 A4 Avant 1.8T that's got a coolant leak but it only appears to happen once the car is up to temperature with the engine turned off. At first I thought it might be the water pump but that would result in a leak all the time as the water appaers to be coming from around that area but evrything is hidden behind the alternator and power steering pump dropping onto the undertray and running off that. Has anyone any ideas, I'm going to have to get it up on the ramps and get underneath to make sure but if I know what iti is I can get the parts to fix it and do it all in one go.

Air con water drain?

could be that the block is getting very hot and once the coolant stops circulating (ie. engine/water pump off) it boils locally and pressurises the system causing it to 'overflow' through the pressure cap.

does the electric fan carry on after the engine is turned off? Did it used to?

How much is it leaking and how often?

Have you checked the engine (via the oil filler hole) to make sure there's no milky appearance to the oil? Possible head gasket trouble.

Hi the fans are fine, had one go three years ago when running the car sits at 87degree coolant temp, I thought it might be the pressure cap on the expansion tank but it's not coming from there. Boiling up causing pressure sounds likely and I've heard of issues with a coolant pipe to the oil cooler leaking but not sure what engine that's on

sounds just like mine a few months back. 'Twas the water pump.
Shame you cant even really get a look at it until the front end of the car is removed.
I knew I should have bought a Renault. 🙂

Could be the radiator expanding when its hot and leaking coolant from a split. Coolant then evaporates off hot radiator making detection difficult. Radiator then seals up when its cold. How much are you losing? P.s. That undertray was the first thing to go on my Golf, what a pain!