Got a mild 512 based on a 400 big block in a dodge 4x4 and it gets hot in just a few miles. fresh engine, good compression and leakdown. New high volume water pump and 4 core aluminum radiator, twin electric fans and 7 blade clutch fan as well. Tried 180,160, and no thermostat. Gets to 240 in about five miles just driving. I has MLR gaskets on it and I pulled the engine out of desperation and pulled the heads off to try and find something. No cracks or signs of coolant in the heads or oil. holes in the head gaskets are normal. I have an old set of Clark copper gaskets from a race engine laying around and they have a couple extra holes in them for more water ports. I read the slits at the top are to vent steam and air as the water runs across the head. Most stock gaskets have no holes open along the bottom. The copper gaskets do. Has anybody had experience opening these holes up to improve cooling?