Possible head gasket

[MB2]

If the head gasket had gone wouldn't there be mayonnaise under the oil cap?

It depends where the gasket has failed and how the channels run - if there is not mayo (water getting into the oil galleries) then it is possible that water is getting into the combustion chamber which tends to result in water loss and (very) high pressure in the expansion tank.

This can be diagnosed by a pressure test of the cylinders and a gas test of the expansion test (for exhaust gas).

If it is the HG (which as many have said is unlikely) before committing to the expense of a repair there is some sealant K-Seal which I tried as a last resort on my mum's Polo which had a bad HG leak and 10 years hence it is still working. I actually put it in before driving it to the garage for her and by the time it was at the garage the problem was resolved so we just had them do an oil & plug change.

[MarkV8]

I believe after going to a proper garage unlike the previous one the driver side aux rad is leaking phew the previous garage said a head gasket, I won't be returning thair. Cheers guys

[rs user]

if its drivers side you can do away with that one...
i"m not 100% sure but even if passenger side leaking i am told you can substitute the drivers one for it if its still fresh
perhaps somebody on here can verify

[MarkV8]

Both my Aux radiators were leaking on the back sides only (so not visible until removal of belly pan) and the only sign was a 'sweet' smell every so often (mostly when going up hills slowly when then car was warm randomly!)

We've managed to find the drivers side aux radiator leaking cheers bud for the advice