I just went on a trip that was 150miles with my 1997 extended cab. The truck is a 4.2 with a manual tranny. I was pulling a 5X10 enclosed trailer that came in at 1037lbs. The only thing in the trailer is a large RC plane. Once I got going the truck kept running just at the last line before that H on the temp guage. It has never been that hot or even close. If I turned the heater on even on the lowest setting the temp went down to my normal running temp (about 1/4 of the way up). So my question is is my radiator shot, or is it somthing else. The truck runs fine without the trailer, and I have pulled a larger trailer last summer on a much longer trip (6X12 over 500 miles with hilly terrain). On that trip it was even hotter out and I ran the AC most of the way. Someone mentioned I may have to much water in my coolant system as well. Please help because my local mechanic wants to start with the radiator and work from there. I hate to replace somthing and it not be the problem.

 

sounds like a plugged radiator. the heater core cooling it is a pretty good clue

 

I'm more inclined to think that the gauge is wrong. The heater core won't generate enough BTUs at almost any setting to effect the temp that much. I would suspect a bad or hyper active temp sending unit. You might try a mechanical gauge before spending major bucks on a radiator. But while you are checking things, check the function of the fan clutch. If it is working correctly and you didn't hear it roaring under the hood, you didn't have an overheat condition.

 

Maybe the thermostat? Maybe it was stuck closed and wouldn't open.

BTW, you forgot the most important piece of info. What kind of rc plane was it? I have a F27 Stryker and a partially built Slo-stick. But I'm not very good at flying.

 

Its a 42% SD extra 260. Big boy. LOL Not the thermostat because it did it again today while towing the trailer.