You gotta purge the air out of the cooling system. The air bleed bolt is on the thermostat housing on the front of the engine roughly under the seat belt buckle area. Top it off in the radiator, get it running and warm enough to let the thermostat open and start exchanging fluids from the engine to the radiator, keep adding fluids until the radiator stays full, turn it off and crack open the bleeder bolt on the thermostat housing with a 10mm socket and let the air bleed out until it starts leaking fluid out of the bolt. Tighten bolt and top off radiator and overflow reservoir. Install radiator cap. Best to have front end elevated the whole time youre doing this. I bought a cooling system vacuum and that works good also. You dont have to worry about the 10mm bleeder bolt if you have the vacuum. A new radiator cap is cheap. Ive replaced the wifes a few times already just for the hell of it when messing with the radiator or cooling fans, etc... good luck!