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I apologize if this has been covered elsewhere to these particular specs, but…
I just bought a 2002 Ford F-150 XLT 4.2L V6 from a family member and the engine is running extremely hot. It only does it at highway speeds (55 MPH and up) but at city speeds it cools back down. Also, the heater blows cooler at HWY speeds but heats up at city speeds. The fan is belt-driven, and constantly spinning, so I’ve been able to rule that out.
I bled the coolant system and at about 195 degrees the coolant level in the reservoir expanded to the top and then dropped back down to where it should be which, I believe, is due to the thermostat opening to let the coolant flow through the engine. When I did this, I discovered that the coolant system was over-filled by about 17 ounces so I removed the excess. I ran the truck both at idle and revved up (2500+ RPM) for about 20 minutes and the temperature gauge stayed between 195-210. The heater blew satisfactory heat at this point. The upper radiator hose got hot and the lower radiator hose was barely warm. Then I drove the truck 20 miles, both at CTY/HWY speeds and it still got very hot (246 degrees). The temperature gauge didn’t go all the way to the red but it almost did. Each time I let off of the gas, the needle on the temp gauge would begin to decrease. When I returned home, the heater didn’t blow as hot before during bleeding. I checked the radiator hoses again and this time the lower radiator hose was hotter than it was when I bled the system. The coolant wasn’t visibly boiling and I didn’t smell anything odd or out of place.
There are no visible fluid leaks. I cannot see or find any vacuum leaks. The upper and lower radiator hoses are soft to the touch, both hot and/or cold. I have yet to flush the system. I feel like the radiator hoses may be the culprit. Does anyone have any ideas?
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My thought is a flow issue.
What is the condition of the radiator?
Is it original? if so it may have a partial blockage.
May also be a issue with the water pump.
It could be the impeller is slipping at higher rpm reducing the flow.The radiator looks to be in decent shape, however it is original. There isn’t any debris blocking it, either. I’m thinking the lower radiator hose is collapsing at the higher speeds.
A possibility…
Might try fixing a gopro aimed at the hose and see what it does during a highway trip.That happened to my buddy’s 2003 F150 after we replaced the exhaust and fuel rims plus brake pads. It was the thermostat. No overheating issues after replacing.
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