No sign of warped head. Mine is cast iron. That's comforting. Changed oil and no sign of coolant in there. Nice and black. Drained coolant. Came out fairly clean with very little scale and no sign of an obstruction in the radiator. Not much came out (maybe 2 quarts), so I'm thinking there wasn't enough and that was the initial problem. Installed new water pump and thermostat. Filled radiator with fresh coolant/water. Started engine and all sounds and looks good. Ran it with radiator cap off for about four minutes. Turned on heat and within 30 seconds again got the overheat light. Shut down. Heater hose still cold, lower radiator hose cold, upper radiator hose warm from thermostat to about halfway to radiator. Engine does not seem overly hot. A slight wisp of steam coming up through open radiator fill tube. Thinking no flow through thermostat, probably due to air in system, and it never did burp. Confirmed no flow past thermostat as there was no coolant when I pulled heater hose and upper radiator hose. Decided to pull the thermostat and drill a little hole in it to let the air pass through, allowing coolant to reach the thermostat. But need a new gasket first. Will try that. If it works to bleed the air out of the system, I will install a new thermostat thereafter. Otherwise, I am completely stumped. Don't think the heater core is cloggled, because that would most likely be gradual. Also, the heater hose would still be warm and the rest of the system would theoretically work properly - just no heat. Any other ideas, or am I on the right track with the air thing?
Friday, February 2nd, 2007 AT 10:42 AM