I'm new to the H.A.M.B. but have read many posts here and hoping for help! I have a '40 dodge coupe that I "finished" several years ago. I have never been able to drive it far due to overheating. I put in a 392 hemi, which is a stock rebuild with new stock water pump, and have a 64 ford 4 core radiator and electric fan. The strange thing is it will idle all day and be fine driving in town under 45 mph. As soon as you hit highway speed it begins to slowly heat up, and up, and up. When you slow down it will eventually cool off again. I've double checked the timing. I tried taking the hood off thinking it could be an air flow problem. I've tried different thermostats. Tried no thermostat. All the same result. More recently I pulled the radiator and had a shop put larger inlet and outlet on it and that seemed to help, but not solve the problem. Half the people I talk to think I need to restrict the coolant flow, that I might be cavitating in the water pump creating air bubbles, and the other half think a high flow water pump might help. Everyone seems to think the radiator should be adequate, but I'm starting to think its just too small. Although I really can't get anything bigger in there. I've tried the water wetter products, and also made air dams to force more air through the radiator. I'm kind of stumped at this point and would love another idea to try!