Same problem as always. Coolant in the oil.

Mike ,I'm no expert but, the fact that it seems to not leak into the oil until it's up to temp makes me think your heads may have a crack in them letting water into the exhaust and oil once the thermostat is open and starts pushing the water through them. I only think that because in a previous post you said there was water coming out the exhaust. If it was a cracked block wouldn't the oil be contained to just the pan?