thunder2

Many apologies if this is straightforward. I've seen the issue replicated but cannot yet find the answer or where to look first.

Lovely A8, D2. A warning message came up saying the coolant level was low. Plus, the car had leaked (lots of) coolant but the engine temperature was still ok, in the middle. Topped up the coolant, drove for a few miles but then saw that the coolant in the expansion bottle was bubbling boiling hot and the lid was leaking, it was that hot! But, the engine temperature was still normal.

She has just had a new expansion bottle so, could it be the cap, the radiator?
I don't think it's the head gasket (which I've seen it could be) so, any advice would be much appreciated.

jfrahm

Could be the cap or a head gasket leak. If it pumps out coolant while you are driving that's more likely head gasket, particularly if the engine is not that hot. If it's OK when driving but gushes out when you park and shut down that is often a bad cap or other pressure problem.

In the USA you can rent a coolant pressure tester essentially for free from the auto parts store.

-Joel.