Figured out my cold truck howl is the fan clutch. Is this normal, if so it sucks. engine off the fan spins but with some resistance. How do they work normally

 

The clutch works as follow when your engine is warm it will engage and make your fan blade spin faster.when its cold it doesnt engage and your fan blade will spin slower till the engine warms.My suggestion is eleminate it and go direct drive with high performance flex fan or ditch the fan altogether and replace it with an electric fan.This will give your engine more power and less drag.Im going to eventualy do this with my Jimmy.

 

I have found mine sound like a jet engine on cold start then quiets down. Think I read its pretty normal.

 

The deal is there is a viscous fluid inside the clutch-if it roars when cold-the fan clutch needs usually needs replacing,because it has solidified,but a strange thing I notice on my Frieghtliner with a Cummins 525 is that the fan clutch roars when the air compressor kicks in,and does the same when the A/C runs at low RPM! But only in warm weather!
HUH? Any explains? Thanks!

 

Thanks Step

 

Uh, backwards. When the clutch is cold, it disengages and the fan roars. As the fluid in the clutch warms up, the clutch gradually engages and quiets down. If/when the engine starts to overheat, the clutch disengages, the fan roars, and pulls more air through the radiator. At normal engine operating temperature, the fan pretty much free-wheels. When the clutch is cold, or the engine overheats, it should be spinning at or near water pump rpm.

Learn about how the fan clutch works from howstuffinmycarworks

 

Once again Hook has it right, cold temps the fan will sound like a bear roaring for the first few minutes after that it gets quiet until neccessary

 

my boss has a 2000 blazer said his doesnt do that. Bugs the crap out of me. May try otherv options

 

The only other option is an electric fan. Keep in mind that with an electric fan you've got far more things that can, and do fail: thermostat, motor, relay, and the associated wiring and connections. On the plus side, you might notice slightly better fuel mileage and less noise, (only because it moves less air). A thermal fan clutch is far more reliable, moves more air and the overall cost is less, that's why manufacturers use them whenever possible, it's a no brainer.

 

My C12 cat in my 9400 does the same thing. I think it has to do with the extra load on the motor creates more heat. And I believe the fans are controlled electronically. Some tractors have a fan override switch.