Fan Clutch

[Stubby79]

Originally Posted by Jez77

I think others use a viscous clutch and sense coolent temp from the waterpump shaft.

This is the basic idea as far as I understand them to work. It needs to be up to a certain temp before the clutch engages. But...they're also designed to run when the engine is dead cold, so the fan will be spinning when you first start up and stop running a minute or two later as it warms up. It's a fail-safe, I believe...if the viscous part of it fails, it will get stuck ON.

Don't quote me on it. Just what I picked up in the brief time I drove a truck, years ago.

[oil pan 4]

The fluid in the clutch will drag more when it's cold.
They are actually designed to spin 25% to 30% of crank speed when "off" with the engine bay at operating temperature. When they are cold they probably spin close to 100% of crank speed till the fluid starts to warm up.
Then nearly crank speed when "on".
They temperature of the air behind the radiator tells it when it needs to be on or off.

[redpoint5]

I'd go electric if one can be had for under $100. Then I'd need to figure out how to trigger the fan based on engine coolant temp.

[Gasoline Fumes]

Originally Posted by redpoint5

I'd go electric if one can be had for under $100. Then I'd need to figure out how to trigger the fan based on engine coolant temp.

Junkyard parts should end up a lot less than $100. You'd need a temp switch in the cooling system and a relay to power the fan.