Does anyone have any idea where my A1 could be leaking coolant from?, it's had a new reservoir, I've had it pressure tested and that was fine, nothing on the floor when left overnight but then it just empties when on a drive, I can't see any obvious leaks from hoses...took it to a mechanic 3 times and each time they just can't find where it's coming from. The car is not overheating at all, I'm just fed up of not being able to get to the bottom of it. Any advice welcome.

Remove the engine under-tray. Check coolant level first and top up, then get car to operating temperature and park over cardboard. Shouldn’t be too difficult to trace the leak. Even determining which side of the engine is useful. Have decent LED torch handy.

Difficult to pinpoint, petrol and diesel version have different characteristics. Suggest you change your mechanic too. Three trips and no resolution?

https://www.audiownersclub.com/forums/topic/14457-coolant-loss/

https://www.audi-sport.net/xf/threads/384742/

A common culprit for invisible coolant losses is the EGR cooler, They have been known to leak internally yet still pass a pressure test.

59 minutes ago, cliffcoggin said:

A common culprit for invisible coolant losses is the EGR cooler, They have been known to leak internally yet still pass a pressure test.

Yeah the mechanic did mention the EGR cooler but said its an expensive part to replace if it's not that, he did mention something about the only way to find out was by-passing it to eliminate it before buying the part...can I ask where does the coolant go if its internal? Does it not have to come out somewhere? (Forgive me if that is a silly Q but I really don't know that much about it).

Thankyou for your reply 😊 

2 hours ago, spartacus 68 said:

Remove the engine under-tray. Check coolant level first and top up, then get car to operating temperature and park over cardboard. Shouldn’t be too difficult to trace the leak. Even determining which side of the engine is useful. Have decent LED torch handy.

Difficult to pinpoint, petrol and diesel version have different characteristics. Suggest you change your mechanic too. Three trips and no resolution?

https://www.audiownersclub.com/forums/topic/14457-coolant-loss/

https://www.audi-sport.net/xf/threads/384742/

It's a diesel, I have tried the cardboard underneath both when hot and cold and left overnight but there is nothing on it to suggest a leak.

14 hours ago, Kirsty said:

Yeah the mechanic did mention the EGR cooler but said its an expensive part to replace if it's not that, he did mention something about the only way to find out was by-passing it to eliminate it before buying the part...can I ask where does the coolant go if its internal? Does it not have to come out somewhere? (Forgive me if that is a silly Q but I really don't know that much about it).

Thankyou for your reply 😊 

If the EGR leaks, the coolant is lost into the engine and out of the exhaust. I believe it is possible to blank it off but your car will then fail the emissions test of the MOT.

3 hours ago, cliffcoggin said:

If the EGR leaks, the coolant is lost into the engine and out of the exhaust. I believe it is possible to blank it off but your car will then fail the emissions test of the MOT.

Not necessarily so. As I mentioned in an A6 C5 topic I only recently discovered the previous owner of my car had removed the EGR valve, however I had no problems with emissions when I put the car through its MOT in September. I realise this may not be the case for everyone but that's my personal experience if it's any help.