I recently broke in my rebuilt 455 (due to a flattened cam) and everything went smoothly. Ran it on the hose for the break-in. I was running a bypass thermostat setup with headers and one overboard dump. It stayed locked at 160 degrees. On the first run on the water it over heated. I trouble shot and found my pressure regulator was stuck fully open causing reduced flow through the engine. Took it apart, found nothing wrong, and reassembled. Second outing, over heated. Re-plumbed to remove the regulator. Same result. Next I ran it on the hose with the thermostat and it over heated. I then plumbed it the old school way without the thermostat (just two connections on the housing, overboard and headers). Ran on the hose at idle and couldn't see lower than 150 degrees at full hose pressure. It should be COLD!. BTW, on the hose my water pressure is about 3 psi at max which is more than the pump makes at idle. There is no water in the oil and except for running somewhat rich it runs great. I'm so stumped. Any thoughts?
