I just bought a 1990 formula. It has this weird overheating issue. I will drive for a few days and then all of a sudden it will just start to overheat. I stop the car let the pressure out add some coolant and I am good for another few days. When I start to add coolant I notice that the coolant has a frothie look to it and there are little black specs floating around in it. It has a new water pump, radiator, thermostat, and radiator cap. I don't smell coolant or see smoke from the pipes or the engine compartment. What could this be? I was thinking a head gasket. Which intern to me would mean time for a new motor. Before I going spending all that money does anyone have any ideas on what it might be?