I changed my head gasket out a little while ago, and after that my engine temp fluctuates from about 180 to 200-210 and it does it all day long whether im pulling a load or not. And it fluctuates back and forth almost as soon as it hits the high and low temp. When it heats up, my engine sounds normal, but as soon as it starts cooling my engine gets a louder rumble/knock sound. just wonderin if anyone had some ideas thanks