My '73 F100 390 has a bad fan clutch. Napa sells two types: centrifugal or thermostatic which do I want. I understand one locks in at certain rpm and the other locks in due to temp changes. Which is better? It's a daily driver with a/c (well, once I find the FE a/c brackets... but that's another story) and runs 70+ on the highway for over 40 miles often. Which one do I need? Would I even notice a difference between the two?

Marty

 

73Custom, you'll find this thread very informative, https://www.ford-trucks.com/forums/s...ght=clutch+fan

-----Buck------

 

Thanks, I agree with the thread and am wanting to keep my clutch fan. But I need to know if a thermostatic clutch or centifugal clutch is better...

Marty

 

Thermostatic always, just like the thread said.

 

Thanks Eric, that's what I'll get.

Marty

 

The Difference is the centrifugal is always on until a certain RPM range, then it starts to slip. 2000-RPM or around there. It never turns faster than that, or slower than idle. Usually used on vehicles not equipped with A/C.

The thermostatic one turns at around/or slower than idle speed, no matter what engine RPMs are at. When the temperature warrants, the fan will begin turning faster and faster until it is full on, turning at around the same speed as the engine RPMs, thus turning faster at higher RPMs, or slower, when the temperature warrants it. usually installed on a/c equipped vehicles, and is by far the superior of the two types.

One thing the other post didn't mention is a flex fan by design, flexes flat the higher the RPMs are, therefore moving less air, than an engaged properly working clutch fan, at the same RPM, because of its rigid fan.

Think of it this way, you are going up a hill doing 25 miles an hour at 3500 RPMs, the engine heats up....

On the flex fan, the blades are flattened and not moving the air as it should, but still turning at full possible rpms....

On the Centrifugal clutch fan, full fan RPMs is reached at 2000 RPM, it won't go faster, so wont blow the air as well, as a thermostatic fan, but does a better job, than the Flex fan, cause it still has a rigid fan blade. After the engine cools, the fan does not slow down, it stays at the 2000 RPM mark, therfore wastes energy, something the thermostatic fan would not.

On the thermostatic Clutch fan, it engages, and turns the fan at full rpms, and with a rigid fan, can move more air than it's flex fan, or centrifugal counterpart, cause it will turn at 3500 rpms under this condition. After the engine cools down, the fan disengages, and turns slower than it's centrifugal partner at 2000 rpms, therfore saves more energy.

Hope this explains it all.

 

Make sure the hole in the clutch coupler is the same size as the water pump nub.

There are 2 sizes - 3/4" & 1/2"