My 98 A4 1.8t B5 has recently developed a massive coolant leak. It needs topping off every 50km or so. I cant find a visible leak and there's no obvious telltale puddles when parked up, so my guess is that it's leaking when under pressure.

I've checked the oil and it's not creamy or frothy, and the plugs don't look steam cleaned so I'm assuming its not the head gasket (or at least I hope not)

The flange at the back of the engine doesn't seem to be wet and I don' think it's the pump - at least I can't see any white build up, so my question is, where the hell is the coolant going?

 

Could be the coolant expansion tank cap not on completely or you may need to replace it, also remove the belly pan and look for any white or pink stream after you notice it has started leaking

 

what does topping off mean? the tank is empty? how does you exhaust look/smell? dont just check the oil, drain it. it probably wont be frothy if coolant is in it. it will be swrily if you know what i mean. im kinda thinking your oil cooler might be leaking. if your absolutley positive it isnt leaking elsewhere, that is a very good probability

 

Sorry, I meant "topping up". The tank is pretty much empty and needs filling. The exhaust is clear and smells like, well, an Audi

I got it up on a lift this afternoon and noticed that there did seem to be a bit of a wet patch coming down from the left hand side, but I couldn't pin point a source.

 

id also check around the turbo coolant supply and return. the crush washers can leak. if you meant left side is passanger side anyways.