Hi Thanks for the reply

The head gasket was done less than 1k ago so hopefully it wont be that

There is no sludge around the oil filler cap or anything like that!

I had a look at the fan switch and the connector looked a bit dodgy but the fan was coming on but it didnt look as if it was going as fast as it usually does!

It would only cool down if I coasted down the bypass at high speeds so would that be the rad doing all the work?

Fan seems to be a bit better now so I think this is the problem!