Hi ive got a smax 2006 2l tdci, recent purchase (60thou miles), the engine has started to overheat intermittently and has water loss but from no area we can see, tried it with thermostat blocked open to see if it stopped it overheating and still does. the temp gauge reads low and then goes from half way to really hot in seconds and engine looses power. there is pressure in the water filler cap when you undo it, water level rises then falls again, we refill and have to squeeze pipes to help water go down. checked the water pump and looks like the timing belt has been renewed aswell a sthe pump. any ideas of what it could be? my dads a mechanic and said its not cylinder head as would do it all the time. fan working fine and all general checks.etc. Where do we go next with it is there a common fault with them that we have missed?
There is no common fault with this engine, we would carry out all the checks you have suggested, but it looks like it may have a head gasket fault, we would have to check it out