If you didn't give the head a hot re-torque when the engine was first put into service, you might have a leaky or blown gasket now. The most likely cause would be a stuck thermostat. Pull the stat and check it for opening temperature with a pan of hot water and a cooking thermometer. While it's out, fill the engine with water to the top of the thermostat housing, take the fan belt off, and start the engine. Quickly, goose the throttle a few times, and look for bubbles. If the head gasket is leaking, you'll see water gush out of the thermostat housing, or at least you'll get compression bubbles. The coolant will start to boil in less than a minute of running without the pump circulating, so be quick with your tests.
Jerry
