My name is Brian I will do my best to help you.if the temp gauge does not go into the red and you still have pressure this sounds like a head gasket problem. what happens in this case the gaskets get small holds in the gasket and the pistons push air into the holes causing the pressure. In this case there are not the usual symptoms of losing water or white smoke. I hope this helps and I wish I had better news for you. if you have any further questions let me know.