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Re: 1990 chevy sub 350 eng runs hot only at...
You may want to check the thermostat for the radiator fan. It controls the activation of the fan. It is found on the hose from the radiator. You should see wires to it protruding. To test, try to remove it and see if the fan turns on. If it does not then the fan is the issue. Check out also leaks in the radiator and the hoses.
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If it was running hot before you replaced the thermostat and the new stat didn't help it, most likely you have another problem. First make sure you installed the new thermostat correctly and not upside down and make sure you have purged all the air out of the cooling system. Your radiator could be clogged and restricted, not allowing coolant to circulate. Your fan clutch could be faulty or the radiator fan is not working properly. You could have a bad head or head gasket causing combustion gases to enter the cooling system. The water pump impeller shaft could have broke---These are the most common causes for an overheating problem. Good luck, i hope this helps.
Check your your radiator cooling fan should come on at about 220 deg. and off at about 210 deg. at idle with a/c off, if it stats to over heat turn a/c on, fan should come on right away, if it dont check voltage at fan motor, if you do have voltage, you have a bad radiator fan motor, more then likely the reason it don't over heat while driving is air is being push through radiator where it cool's the coolant before it goes back into the engine, at stop's no air running through and never cool's coolant .
if you have replace the thermostat and rad cap, after the thermostat did you let the system burb it self. there might be an air pocket in the system. you can also check the strengthof the coolant if its low it won't remove the heat. also check the front of your rad the fins make sure that it's not all plugged up with dirty, bugs etc. after you get the over heating under control then we can look at the high idling
hope this helps
You can tell if your water pump is running backwards by the way the radiator fan is running. If the ran is pulling air from the radiator then the water pump is running the right way, if it's pushing air toward the radiator then your water pump is running the wrong way too. There should be a sticker on the fan shroud or on the hood to the direction the serpentine belt should run. IF the water pump is running the right direction, then it needs to be replaced. Good luck and hope this helps.
The first thing that I would check would be the level of the coolant. This is VERY important. Other things to look into would be a clogged radiator or a malfunctioning water pump. It would more than likely be one of the first two.
you can check if the water pump is working by feeling the top rad hose , if it is hot it should circulate into the rad and the rad should be hot at the top and cool at the bottom if the pump is faulty there will be no circulation of hot coolant into the rad. I suspect your head gasket might be blown if you are getting pressure built up in the rad. in that case you will need a new gasket and have your head skimmed
turn your heater on to max heat and high fan. then see if you can feel the hoses on the firewall for heat they should be hot. make sure that the fan unit on the radiatoris working if the upper radiator hose is hot the fans should be running if they are not that means that either the relay is bad the thermo sensor is bad or the fan unit is shot... please rate the solution..........thanks