L98 that was driven with a stuck thermostat about two miles before noticing the overheating condition. That's two miles after starting the car when it was cold. Now with a new thermostat I can run the car for a few minutes before the white smoke appears and that will happen before reaching operating temperature. When I kill the engine the radiator cap spurts out about 8 Oz of coolant the quickly stops. Seems to me that it's got to be one of the big three: heads, head gasket or block. Is there any reason not to start pulling the heads?