no power foam in radiator
Do a compression check on all cylinders. Compression gauge screws in the spark plug holes and turn the engine over a few turns. I think you will find a blown head gasket leaking into one of the water jackets. Makes for foam in the radiator. You can check them one plug hole at a time and just remove the coil wire so the engine won't start. One cylinder and probably two, "cylinders adjoining" will check a considerable bit lower than the rest.