Foaming coolant under heavy load, bad head gasket?

[wwirz]

It could be that you overfilled the cooling system. Mine also "frothed" when I overfilled it. As a starting point the coolant level should only be as high as the baffles. You likely do not have a problem at all except for too much coolant in the system. It stopped coming out of the bottom of the cap because the coolant found its own level. Drive it, have fun, keep an eye on it.