Found the problem - air pockets in the cooling system. Ran the motor without the radiator cap for 45 mins. just like old fathfull, burped 3 separate times, repleneshed lost fuild after each air pocket release. Let run for 15 more mins. with coolant level full. Then put on radiator cap back on after topping off once last time. Let run for another 30 mins., never overheated. Problem solved. Same as bleeding air out of the radiator in an old house every fall.