I didn't build the engine. The way it was acting, I figured it didn't have a T-stat at all. Today my suspicions were proven correct. So I put an original stat in, the bellows type. I stove tested it first ofcourse. Well! I should've done that a while ago. The heater works better, It's holding operating temp, and fluctuating much less. I really think that was the problem. We will see on a hot day. An old timer friend of mine said a t-stat will keep the engine cooler. Because it slows down the coolant flow in the rad, allowing it more time to cool off. I've heard that before, but didn't have the experience to verify its validity. I'm glad I pulled it all apart. I got to replace all the rtv with gaskets, fix a belt alignment issue and verify the condition of the distribution tube.