I think my car has an air block somewhere. It starts every time, cold or hot, with no sludge or mayonnaise anywhere but when driving, the car gets hot and starts making gurgling noises from where you put the water in, as if it is going through to the radiator. It does get really hot and the water fills up in the header tank, then drains and squirts into the tank. Someone said it sounds like an air block and suggested to drain it and start over. What do you think?