Overheating problem help please...

[kelviny]

1991 B2600I 2wd. New head (rebuilt) cylinder,gaskets,water pump,thermostat,belts are good (tension) back flushed radiator, ran engine with radiator cap off to see if air was coming out. radiator less than 2 years old. Runs fine (about 40-50% on gauge) until I hit a 2 mile hill going home then it starts to get really hot 90% on the gauge. Fan working but someone said that the fan should have more power. Are you supposed to be able to stop fan from spinning if you held it right before you started the engine then ran it?

[BuckR]

I had the same problem on my 91 B2600i w/215,000 miles on it. I had a shop replace the water pump, thermostat, fan clutch and flushed the radiator all with no affect. They even blew the head due to overheating trying to diagnose it. Turned out to be a partially clogged radiator that made a cool spot in front of the fan clutch which kept it from engaging the fan when excess heat built up (might make your's seem weak). I diagnosed it by warming up the truck and then shutting it down and CAREFULLY feeling the radiator on the engine side. It should be pretty uniform temp all over. Needless to say the shop ate the cost of all those parts and a new head gasket! I know you said the radiator was fairly new but so was mine at the time. This is a cheap way to see what's going on. By the way, the fan is stiff to turn by hand even when the enginge is cool until you get some high rpm to make the clutch work. Mine "roars" when I start driving and then gets quiet in about a second. That's why you shouldn't try to restrain the fan when turning over the engine. Good Luck and let us know what the fault was.
Tom

[kelviny]

Thanks, I'm going to change the fan clutch because I couldn't feel any difference in my fan's resistance from running the engine for 2 minutes vs getting motor up to operating temp (as per Haynes manual) I'll be sure to test my radiator as you suggested. Thanks kel