That's right, I don't think my engine is making enough heat. It's a slightly warmed up 350, Vortec heads, cam, 9.25:1 comrpession, etc... The trouble is that it takes forever to get up to temperature. My electric choke pulls off too soon and then my truck starts bogging down every time I step on the gas. The cooling system is working properly but I still tried replacing the thermostat just to see what would happen. There was no change. I would like to think I am losing a lot of heat through the heater core, but I'm not. It stays fairly cold in the cab as well. When I'm cruising down the highway, I barely make enough heat to open the thermostat. I guess I'll just put a resistor in line with my electric choke to slow it down. Oh yeah, there is no exhaust crossover in the intake manifold which probably has something to do with bogging down.