Mechanics

RANDOM OVERHEATING

1997 Ford Expedition • 4WD Automatic •

1997 Ford Expedition 4.6 with 197,000 miles randomly blows cold air. Then the temp gauge goes all the way up and the radiator overflow blows. I shut the car off relieve the overflow pressure and start the car back up and it is fine. I have replaced the thermostat and the problem continues. There is no pattern. When the temp gauge tops out the car immediately governs the engine speed down as well. Does anyone know the cause?
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Dougwo
December 20, 2010.



Could be a couple of things, the radiator cap could be bad, also coolant needs to be 50/50 otherwise you will have a problem, also air pockets.

Legitimate007
Dec 20, 2010.
Ok. Just replaced the cap. Coolant is fine. I was driving back to my shop after the cap was replaced and in about 2 miles the cool air started coming through the heat and the truck started to slow down again and over heat. I get out of the truck and crack the radiator for a couple seconds and get back in the truck and all is fine. It will not overheat again until the truck sits off for awhile. It only happens shortly after the truck is run after a period of non running. The truck runs fine with no power loss except for when this issue starts.?

Tiny
Dougwo
Dec 20, 2010.
Ok, then we need to verify that the radiator fan is coming on when the gauge signals that it is beginning to get too hot. It sounds like its not coming on if its overheating like that, if this is the case, then your problem is one of two things, the fan is bad, or the relay switch is bad.

Legitimate007
Dec 21, 2010.
Thanks for your help. The fan is running. I took the car out last night after replacing the rad cap. Still the same. The temp gauge bottoms out. The air gets cold then the gauge shoots up all the way. The engine idles down. I turn the car off for 30 seconds or so. Start back up the gauge drops to normal. The rad stops overflowing and it will not overheat again until it sits for awhile. I have driven it for 30 minutes after an episode and it will not overheat again until it is off for 20 min. Or so. The check engine light does go on but a scan indicates a overheat episode. It does not specify why.
Thanks

Tiny
Dougwo
Dec 21, 2010.
Bleed the system and top off the coolant, if that doesnt work, you'll have to have it pressure tested, to reveal if the heater core is clogged and or the radiator is clogged

Legitimate007
Dec 21, 2010.