Today I was cleaning up my greasy handprints and generally inspecting the general condition of a variety of things. I grabbed the main fan blades to more or less check out the viscous coupler resistance. It turned real easily by hand with the engine completely colod. I guess that means I need to replace it?

I guess the cooling system will be one of my next major projects now that the driveshaft install is complete.

 

Wouldnt hurt to replace it, check the tech section for the "how to" with part numbers and such included.

 

When cold, expect it to turn only one or two blades worth of rotation. The internal fluid settles, and provides maximum coupling. When engine cranks up, fan should make a "roar" that goes away in a minute or so, the air flow is max at this point, then drops off. Coupling is dropping from 75% to about 20%, to save gas, etc. When warm (normal running temp) and you switch off the truck, the fan should still have some resistance, but not a full rpm when spun. Ones that "free wheel" have lost some of the internal fluid (looks like oil on front of fan), and can't re-couple when hot. When face plate of fan gets to about 170 degrees from radiator air flow, which is about 200-210 water temp, the fan starts to recouple and will be stiffer, and blow more air. If radiator is clogged, you can have a cold spot where the air hitting the front of the clutch is located, likewise you can have trash in front of the radiator also blocking air flow. The write up on the Chevy fan clutch conversion is good, and for $50 and drilling out four mounting holes in the fan you are good to go.

Normally a weak fan clutch shows up as big temp rise when not moving in traffic or just idling. The fan only works at low speeds, at highway speed most air comes from the vehicle motion - just try holding a pizza box out the window.

search for the post with "doing the viscuous fan conversion" which has more info and pix of completed unit.

 

Danny....any thoughts of converting to an electric fan ? I've thought about this myself for a while , but havent done anything about it yet. Kenlowe ( in the UK) makes a "kit" for our trucks...looks good but sorta pricey by the time you could get one here....

 

You need to be concerned if you spin the fan when the engine is hot and it still spins easily.
Take your clutch to a local parts store they can match it up with a Chevy truck, standard duty clutch for around $80.

 

$49 at Advance, $56 at O'Rielly - be sure to get standard duty, not heavy duty. The HD operates at a slightly lower temp, so you basically "roar" more of the time and MPG will suffer. I went with HD, and then swapped to the regular because I had failed to listen to wiser wrench wigglers. You will need to follow the sticky and enlarge the fan blade mount holes slightly and use new bolts. Fan clutch is for a 2000 Chevy Express, 4.3 liter, no AC.

 

Savannah,

I appreciate the details. I will go ahead and plan to do just that. And replace the rad hoses at the same time.

Thanks gentlemen for everyone's input.