I diagnosed my overheat problem, hot upper hose cold lower hose, as a stuck thermostat. I pulled the coolant pump and replaced the thermostat. After roadtest: radiator heated up, lower hose heated up, fan came on, fan shut off, no overheating. My wife drove to work (12mi) no overheating. On the way back overheat problem is back. Is it possible that I got a bad part? What a pain to redo this repair!
I don't think the fan came on because the lower part of the radiator stays cold. If I remove the reservoir cap then there is coolant recirc. The new thermostat fixed the problem and the system functioned normal, but not very long.
You have to check to see if the coolant is still in the system. Did the heat on the inside of the car fade to cold? If so I would suspect low coolant level.
Yeah but he gets plenty of heat on the inside of the car so I would rule out the water pump. I would also guess he has not had the heater recall either. I don't recommend the recall in areas that get cold.
I am thinking that the fan is not coming on, or there is no air flowing through the radiator. Maybe the radiator fan switch is bad, or the fuse, or the wiring, or the fan motor itself. He has a new thermostat but I would ask if the radiator does get hot or not.
It will overheat within 5 minutes. Again the lower part of the radiator stays cold so the switch doesn't close and fan doesn't cycle. The thing that bothers me is that a new thermostat fixed it but only for a short time.
Did you use any 'stop leak' in it? Are you sure that there is plenty of coolant/water in it? You might want to take off the top radiator hose and fill both the engine and the radiator that way.
BTW 5 minutes is mighty quick for your engine to overheat if there is coolant in it. How is the heat inside of the car? If bad:................ Possibly low fluid level or bad water pump. If good:.................. Might be another bad thermostat. (I have seen a thermostat that was stuck open by it's bleed hole device) Of course in your case the thermostat is stuck closed. :-(
And then it could be an engine problem like cylinder head gasket, or maybe cracked cyl. head.
You might want to pull the thermostat out and throw it in a pan of water on the stove. Is it closed when cold? Does it open before the water boils?
You might have a bad thermostat. If the thermostat checks good (testing it in a pan of water on the stove), then I would check the water pump. While you have the thermostat housing off, try turning the impeller in the pump with a screwdriver. Don't push hard enough to break it, but if it spins easily, then the water pump is a problem.
I'm also a little suspiscious of the head gasket. With the engine cold (like after sitting overnight), start it up. Rev it a little (not high, maybe 1500-2000 RPM's a couple times) and shut it off. Now, listen carefully as you release the pressure cap. Do you hear hissing as pressure escapes? If the system pressurizes when it's cold, then you have combustion pressure (and heat) leaking through a failed head gasket.
I pulled out the thermostat and left it out. Engine overheated but, the fan didn't come on. I jumped the fan switch and it worked. Took off the fan thermoswitch and tested it in boiling water. It (only a few months old) failed continutiy test so I replaced it. Car still overheated but, cooled down after I jumped the fan and let it run. Checked the new switch in boiling water and it also failed to close. Will take it back tomorrow. I didn't know how to test for head gasket leak but I'll try that pressure test.
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