2003 chevy blazer head gasket

I had my head gasket blow a couple months ago
and after they were replaced my temperature
would jump all around. It was still a little cold out
so when I drove it the temp would go all the way
down but now that it's warmer out the temp jumps
waaaaay up and stays there. Goes down very little
when I drive but when I get 10 to 15 miles to my
destination the motor smells hot crazy hot. Just
trying to figure out what it could be. My mechanic
has no clue.