How much pressure in the coolant system is acceptable after leaving it over night, went to undo it today and there was a small release of pressure is this normal as I know when there is a lot it indicates HG failure.

Think I'm more paranoid then anything but is a small release enough to presume HG needs sorting?

There's no mayo, no white smoke coolant goes down a little but not much

This is normal. I'd of thought head gasket failure would leave no pressure in the system as it would leak out through the failed gasket ??

A small release would be acceptable, probably hard to quantify really on here, if it sounds like you've just opened a bottle of fizzy pop every morning then I'd keep an eye on the system, for coolant levels dropping in the header tank etc.

This is normal. I'd of thought head gasket failure would leave no pressure in the system as it would leak out through the failed gasket ??

It depends how the HG has failed, it can increase coolant pressure if for example exhaust gasses are escaping into the cooling system, as the op mentions two things that are *possible* symptoms of HG failure, they're both normally also mutually exclusive. A system that's loosing coolant wouldn't normally hold excess pressure unless the leak was pressure dependent in which case it still shouldn't hold pressure when cold as coolant will have been expelled when it was hot.

Personally if it's only a very small amount of pressure i'd not get too excited but if it's more than a faint hiss then i'd suggest getting a sniffer test done. It's cheap and quick, you can buy your own kit or you can get a garage to do it at minimal cost.

^^

Makes sense . Thanks for info.

Cheers for help guys, I have to change expansion tank anyway due to the faulty sensor in it, so will go from there

There is a definite hiss but more like half opening a fizzy drink doesn't hiss for very long if that quantifies the sound.... it's doesn't explode in my face put it that way lol

Might just go and get a sniff done to be sure it's cheap from what I read?