Fan clutch

[RodnRudy]

I need to replace the fan clutch on my 68 SWB. It has a crate 350 with short water pump.
Question is what is the difference between a thermal and non thermal clutch?
The truck will be a daily driver and has a three core radiator with shroud.
Which fan clutch will be the better option? Thanks

[tdangle]

I just replaced mine with a thermal unit. the difference is that thermal locks up due to temperature, the other works on speed, basically locking up at slow engine speed and freewheeling at high engine speeds.

[Stocker]

Precisely what he said, and a website to back it up: http://www.aa1car.com/library/cooling_fan_clutch.htm

Definitely go for a thermal unit.


"There are two basic types of fan clutches: thermal and non-thermal (also called "torque limiting"). Thermal fan clutches have a temperature-sensitive bimetal coil spring on the front that reacts to temperature changes. When the air coming through the radiator is hot, the spring expands and opens an internal valve that reduces clutch slippage. This causes the fan to spin faster for increased cooling. As the air cools, the spring contracts and closes the valve. This increases the amount of clutch slippage, allowing the fan to slow down and decrease cooling.

The clutch consists of a fluid coupling filled with a silicone based oil. The area between the teeth on the clutch plates is filled with silicone fluid. An internal valve opens and closes a passage between the main fluid cavity and a fluid reservoir. When the passage is open, fluid enters the clutch and makes the fan to turn faster. When the valve is shut, fluid flows back to the reservoir but doesn't return, causing the clutch to slip and the fan to turn more slowly.

The non-thermal (torque limiting) fan clutch doesn't have a temperature sensing capability. It reacts only to speed, slipping to limit maximum fan speed to about 1200 to 2200 rpm depending on the application."

[RodnRudy]

Thanks for the responses fellas, thermal fan clutch it will be.

[stsalvage]

one thing that i did not read in both reply's is don't use the flex fan they are killers or you will have a new hood ornament sticking throw your hood

[RodnRudy]

No worry on the fan, I'll be using the original.