I have a 1974 Pontiac Grand Am with a 400 cu in engine, TH400 tranny. Unknown actual miles. It had been running a little hot (but never overheated), so I replaced the radiator and the water pump. Now after driving about 100 miles the radiator will be down about one gallon of coolant. There are no leaks. I can smell the coolant when I shut off the car. Head Gaskets?