It turns out my original fan clutch has been bad since I bought the truck used in '05 and over 100,000 miles ago. The engine's never roared like it does now, and it used to get up to op. temp real fast. I've never had a problem with it over heating, I've hauled bed fulls of stuff, towed numerous trailers, been stuck in amazing Houston "rush-hour" traffic in 100+ degree days.
But now my daily commute is 15 minutes side street traffic, if I keep the tranny in 2nd gear at 40 mph @ 2500 rpm the fan is still roaring like crazy. So now my truck doesn't get up to my normal op. temp (recipe for sludge I think I read somewhere here).
My main question is I'm thinking about returning the new fan clutch and just staying with the old one (until I do the e-fan mod). Does this sound like a bad idea?
Next ? is more of a how it works deal. I think that when the clutch heats up enough or spins fast enough it will disengage and let the fan blades spin at a lower rate when the RPMs are high. But i'm confused why it roars so much at idle and very low RPMs. Wouldn't the fan blades still be spinning at the same speed as crankcase at idle with a good or a bad clutch?
Sorry for such a big post.

 

Sounds like the clutch has failed locked to the water pump shaft. Can you spin the fan when the motor is off and cold? The fan will turn easily when the motor is cold and no cooling is needed. As the airflow through the radiator warms up, the fan clutch grips the water pump shaft tighter making it spin with the shaft. The goal is to have the fan cool the radiator only when the forward motion doesn't provide enough air flow.

I guess you could put the old clutch back on. It'll just pull more ponies from the motor than are necessary.

 

I haven't done the spin test with the new clutch yet, but the old one would not free spin at all, hot or cold. Honestly I'm not too overly concerned about a couple horse powers lost or gain. But now I've had a few cars think I'm trying to race them off the line at red lights because the engine roars so loud lol.

 

That confirms a frozen clutch.

 

Okay so I tried to spin the blades this morning with a cold engine and new clutch still on and they still wouldn't free spin. I'm still confused that if my old clutch was frozen why the blades never roared like they do now.

 

Did the fan turn at all? It won't twirl forever, it'll just turn easily. Hmmmm, can a bad water pump roar? I guess it's possible.

 

Nope, it turns with a lot of resistance and as soon as I let go it stops.

 

OK. I'd say this one's diagnosed. Just for giggles, I tried a brand new one at the local dealership recently. It was easy to move and probably went through a full revolution before it stopped.

It sounds like the new clutch is bad, too.