I drive a 74 chevy truck. I had to change the thermostat beacuse it was suck open causing the truck to not get very warm. I replace it, and after that it would go almost into the red and then come back down to normal operating temp and stay there. This only happens when the truck is trying to get warm. I thought I might of gotten a hold of a bad thermostat. So I replaced it again and now the same thing keeps happening. Any Ideas. I dont want to drill a hole either.