I work with gas turbines. Parts of the engine work in a gas whose temperature exceeds the melting point of the metal it passes over. However, that does not make me an expert on the likelihood of pistons melting at the compression temperature because of the cooling systems in play in a reciprocating engines. Not wishing to flame you either Smokes, but sometimes it is better to be though a fool than get on your keyboard and remove all doubt!
If Mark says it's the thermostat, it's the thermostat, and if he says they work around 90 deg, they work around 90 deg - all his advice to me has been spot on. It isn't what you know, it's what you have done to apply your knowledge in context that counts. Mark has done that, we haven't - listen and learn.
MkV Golf is it? You have my deepest sympathy!! Check out the pages on Honest John (.co.uk) about the Golf MkV, and then look at the same age Focus. A mile of faults for the MkV and a few for the Focus. Just where does this fabled VW reliability come from? We have three VW cars in the pool at work, and each of them has failed on a journey in the last twelve months - two of them are '10' plates!!
Change the thermostat Big G, and I'm sure you'll have a cure.
