I have an 85 F-150 inline 6 that is overheating in traffic. In clean air it is fine. It has a new water pump and thermostat. Someone suggested that it could be the clutch on the cooling fan. My Hanes book says that if you spin it by hand and it spins freely 3 or more times, the clutch is bad. It doesn't even spin 2 times by hand. It also says that as the engine runs and starts to warm up, I should be able to hear the fan get louder. I have not been able to hear any change in the fan. NAPA wants $55 for a new clutch. I would like to be sure it is the problem before I spend that. Any ideas on how I can really tell if it is the fan clutch?

 

First- are you sure the motor is overheating? Don't put any faith in the stock gauge, they are notoriously inaccurate and sometimes flat out wrong. But lets assume it really is.

So it overheats in traffic, but not driving. There's an airflow problem, which is most likely the fan and/or clutch. Check the fan for bent or broken blades.

Being able to spin the clutch twice? That seems a little loose. Mine will go maybe 1 turn. That Haynes test is generally regarded as inaccurate.

I'd vote for the clutch as well. Since the pump and thermostat are new, really the only thing left is the fan clutch.

A radiator flush wouldn't hurt either. Easy saturday mechanic work. Just watch, the radiator drain pet****s are typically broken or seized on older trucks. You have to unscrew the handle, and let it all leak out of the gap there. Get several buckets to catch the various drips.

LOL- it censored that

 

The correct test for a fan clutch is described in this thread.

My personal way to test a radiator is:
1) with the engine cold, jam the fan so it can't spin, or remove it;
2) hose down the radiator & start the engine, allowing it to warm up slowly at idle;
3) when the thermostat opens, the water on the radiator fins will evaporate quickly, so observe HOW it dries;
4) if a line appears & remains distinct for a while, it means the tubes that stay wet are blocked, and little or no coolant is flowing thru that part of the radiator (usually the bottom, where sediments collect);
5) if more than ~20% of the radiator stays wet, replace it. If more than 10% stays wet, consider replacing it soon, or at least getting it backflushed & pressure-tested.

 

Had the same problem with my 1994 4.9. All the same symptoms, Ended up putting a new radiator in it and It solved all my problems. That what i got for not flushing it regularly!