Hopefully someone out there has a suggestion for me. I have a 1997 F150 4x4 with about 105k miles. At 58k I had a new engine (4.2 v6) installed by ford due to a recall related to the head gasket if my memory is correct. About 2 months ago, I was driving up interstate 5 in CA going about 70 mph. It was about 107f degrees, and all of a sudden I look down at the temp gauge and it is almost to the redline. I quickly pull over and by the time I stop & put the truck in neutral (manual) the temp is down to the 1/2 point. I think it is odd, and maybe a fluke, but as soon as I hit about 60, the temp goes to the redline. I turn off the a/c and drive with the heater on high & windows down to keep from overheating. So I think it must be either a blockage in the hoses or the thermostat is bad. A mechanic checks the hoses with a laser thermostat and coolant seems to be moving into the engine and back again. So he replaces the thermostat, but same problem - it overheats (or almost does) once I hit freeway speeds. Oddly driving around town, it seems to do OK. What could cause this? The first 5 years, the temp gauge never moved, now it jumps to the redline, but then shows cooler in under a minute. I dont think there is any way that the temp. of the coolant is changing that quickly, but I dont want to be wrong and damage the engine. Any ideas would be appreciated.

Thanks

 

it's going bad

 

I would agree with TexfordD. However before doing that when you say it hits redline and you pull over does it smell like it is overheating? I am guessing that it don't smell like its overheating and thats why I would agree with TexfordD, its an electrical issue with the sender.

 

he does'nt mention that it starts to miss real bad when it redlines....it would go into the four fire mode at over heat...thus the sender for the computer is reading fine ,the sender for the gauge is skewed...elementery watson LOL

 

Check the return hose from your radiator to the engine. Sounds like the hose is collapsing at higher rpms.

At operating temperature, i.e., the engine is hot, have somebody step on the gas while you observe the radiator hose. If it collapses, you've found your problem.

 

Have you checked for pressure in the coolant system? Could be a slight crack or hole in the system. under higher speeds the pressure is increased...???

Just a thought.

I had an altitude induced problem with my old chevy...in the city, at sea level it was fine. Once I hit 5,000ft., well that was a diff. story.

Good luck

 

It sounds like your fan clutch is bad . At lower rpm it will work fine , but at higher RPM will freewheels and does not spin at the rate it should .

 

The fan is completely uneccessary at 60 mph.

My parents car would over heat on the hyw with the A/C on, but not with the a/c off. I drove it back across Kansas with the windows down and 110 degrees. What a long trip. I got it home and it too would do fine around the city w/ a/c. The problem was a partially blocked radiator. I assume that the engine had to work harder to get to and maintain hyw speeds.

 

Spaceman's right too. Bottom line is something's being blocked at high speeds/engine rpms. I'm assuming airflow is okay, so it has to be water flow.

Check the hose as I suggested and check the radiator for cool spots.

 

it is mostlikely air in the cooling system. there is a bleeding procedure i do not know it however.

what you are decribing is the perfect scenario for air. what happens especially at higher speeds is that as pressure builds air will get around the sensor so it will actually read air/enigine/surrounding metal temps. i have seen it many times before and most techs miss diagnose it for a bad thermostat

pressure check your rad cap (if you have one)

good luck and let us know what happens-

 

5+ year old truck with 100k. Yeah you got a new engine but you didn't get a new radiator. Go to a radiator shop and have them flow test your radiator.

Since you live near an area with heat you might want to upgrade to a bigger radiator with more cores if it's available.

 

I had the exact same problem with my truck and guess what? Its the radiator. I flushed the coolant system, changed the thermostat, and the fan clutch with no change with the over heating problem. I got a 2 run radiator instead of a single. It was only 10 dollars more. I kept the old radiator and and the water flow was reduced. I put the radiator on one end and ran water from the garden hose thru it and it could not handle 1/2 the water flow coming out of it. My radiator cost was 215 for a 2 core with the fiitings for the tranny cooler. Get a radiator cause the problems your having were the same as mine. Good luck.

 

Not sure whether this is related but once after a flush and coolant change, I didn't bother to uncap the reservoir cap to "bleed" any air in the system. After a short time driving, the temperature guage fluctuated like crazy. The needle would move up and down wildly every 5 seconds or so. So I immediately stopped and slowly released the pressure and everything ran normal after that.