HELP! Fast and excessive heating > 225. Thermostat & hose replaced (top hose was split but themostat didn't appear that bad)....no detectible leaks now. heATER THrOWS HEAT ok AND WATER IN RADIATOR HEATS QUICKLY....so it seems like water is circulating through the engine. While driving, temp gets to > 225 quickly and varies several degrees for no apparent reason. After driving a while the preignition begins (engine rattling) and engine dies. I can't see where or if water is getting into the oil (bad head gasket?)..it seems ok but need positive check.
What else could cause this?