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Discussion Starter #1
My '95 F-150 overheats at highway speeds even though I have replaced the thermostat and water pump. The pump was leaking, being the reason for replacement, and I changed the thermostat just because of the high mileage on the truck. But now, at sustained speeds at 55+, the temp. gauge pegs for 10-20 seconds then falls back to normal temp, hangs there for a couple of minutes and then starts climbing back to the high temp side of the gauge. Just driving in town in stop-and-go traffic the temp. stays in the normal range. Could the lower hose be collapsing? I've kept an eye on coolant level and that's at normal level. I would appreciate any insight to this problem that anyone might have. Is there a way to replicate driving conditions in the driveway? Maybe place the truck on jackstands and block the airflow through the radiator.
 

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And I would advise against trying to run the truck at highway speeds on jack stands. That's a recipe for disaster.
Do you have a flex fan or a mechanical clutch fan?
 

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Discussion Starter #5
Thanks for the reply.
I didn't mention that I replaced the radiator about four years ago and I do try to change the coolant every other year. The coolant looks clean. This truck has been a good one, bought new, and now has over 228,000 miles. I try to stay on top of the preventive maintenance.
 

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Have you properly purged the system of air? Maybe at highway speeds the water pump can't push the air out of it that collects there.
 
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