The clutch gets stiffer as it heats up.  The fan doesn't need to push much air on a cold engine.

9 hours ago, Zed Head said:

The clutch gets stiffer as it heats up.  The fan doesn't need to push much air on a cold engine.

That's the strange part, the most air the fan ever blows is when the car is first starting

See how many rounds you can spin the fan by hand when it's cold. I can't get one complete rotation on mine.

I found the restore clutch from Blue's Tech Tips. It's a download now, the original site is unavailable.

FAN 280zx Datsun rebuild fan clutch (1).pdf

 

3 minutes ago, siteunseen said:

See how many rounds you can spin the fan by hand when it's cold. I can't get one complete rotation on mine.

I found the restore clutch from Blue's Tech Tips. It's a download now, the original site is unavailable.

FAN 280zx Datsun rebuild fan clutch (1).pdf 316.72 kB · 1 download

 

Just gave it a shot and when its cold I can spin it about a quarter turn which seems pretty good.  That said, when it's warm I'm able to spin it considerably more than that, shouldn't the opposite be true because it's supposed to grip harder to move more air when warm?

It might be bad.  Don't forget that fan only matters at low vehicle speeds.

15 hours ago, Zed Head said:

It might be bad.  Don't forget that fan only matters at low vehicle speeds.

So while driving, if the fan was directly connected to the engine instead of through a clutch for example, cooling performance wouldn't really change all that much?

I understand the logic in having the fan clutch heat actuated BUT I think it would have been an improvement to have the fan clutch only actuated when the vehicle slowed below 10 mph.. As Zed Head stated "The fan only matters at low (or no) vehicle speed.

I don't know how but mine blow with the motor rpm's until the thermostat opens. I crank them at least once a month holding at 2,000 inside the garage, the fan gets quiter and then I see coolant flowing across the top of the radiator. 

This is something you guys already talked about I'm guessing but I finally read what explains it to me in simpleton speak.