It is just pressurizing a little bit. I let the motor cool down completely then the radiator still is pressurized when I remove the radiator cap. There should be no pressure in the cooling system once a motor completely cools down so I know the orings are leaking a little. The motor never overheated. It seems like I am not getting a perfect seal with the domes on the cylinder. It is a cub cylinder and a Noss head. I guess I need to check the cylinder for flatness. Any chance the domes could be damaged in some way? I was thinking of sanding them down a little so they put more pressure on the orings.