[cooperino]

Originally Posted by FrankF3

It just occurred to me and I hate to say it, would a blown head gasket behave like this?

If you had a blown head gasket, you would likely have smoke from exhaust and be adding coolant from time to time.

Couple of questions. Are you certain that you gauge and sender are providing accurate temps? When its running with cap off is it bubbling out? Have you checked the water pump? If fins on pump have deteriorated flow would be diminished. I ask because you say it only happens at lower engine speeds. Maybe the pump is able to move enough water at higher rpm