Adding a clutch to my fan - part?

[Ekliptix]

My 402 is very slow to warm up. I'd like to add a fan clutch to delay the fan from spinning, until it's warmed up.

Any ideas how to find the right clutch fan + parts that will work? I'm running the OEM fan shroud and the fan from my C10 when it had a 350. Stock rad.

[Steeveedee]

That's more likely the thermostat not closing all the way. In any event, my fan has the following numbers on it.

3947772 914087 L69

and I have a NAPA 2747 clutch.

My engine is the L47 402, so I don't know if the L69 on the fan means anything.

[Stocker]

Agreed, check the t-stat first. Clutch fan is a great move, though more for cooling than a faster warm-up. It will reduce rotation (until more is needed) but does not actually 'free-wheel'. NAPA's Hayden #2747 mentioned above is an excellent heavy-duty clutch unit. That's what I have, along with the stock 7-blade fan. My K20 never overheats. Your stock shroud accommodates an 18" fan -- I recommend a 7-blade fan, though a good 6-blade should do the job.

[sick472]

I know it's a bit outside your question, but electric fans with the controller have this ability. I have an electric set up that has a 160° thermostat (mechanical) in the intake , but the fan does not operate until 180° is achieved. On cold days on the highway, my fan does not even kick on.

Back to your specific question: I have had clutch fans on most all of my cars/trucks and they all spun at idle speeds. Are there such mechanical style clutch fans that do not?

I would suspect a stuck open thermostat too...like Steve mentioned.

[Ekliptix]

I think you guys hit the nail on the head with the thermostat. I'll check that first. Chances are, that's the culprit.

[68 P.O.S.]

Another vote for the thermostat. A fan clutch wouldn't help with that because it's supposed to spin at idle.

[Stocker]

Throwing this out there for general info on clutch fans.
One thing mentioned is % of rotation speed when engaged / disengaged for standard-, heavy-, and severe-duty thermal clutches.
https://www.haydenauto.com/en/produc...-types/thermal

[Big Kev-O]

I don't think adding a thermo clutch fan is going to help your situation much due to how they operate. It will reduce the speed of the fan but on a cold start you will discover the fan is actually engaged until the fluid is pumped back into the center reservoir. This can take over 10 minutes and even longer in cold temperatures due to the increased viscosity of the fluid. After the car sits the fluid falls down from the reservoir into the shear plates which causes the fan to be engaged upon startup. I know this from experience because I started with a brand new severe duty clutch and my truck sounded like a street sweeper for the first 10 minutes. All I could hear was wind then right before I got to work it would disengage and my truck would sound so much better. I switched to a regular duty fan, same issue. I got tired of hearing the fan over my motor and switched to dual electric.

This video explains the general operation but does nobody ever tells you that the fluid will drop down into the shear plates and cause the fan to be engage upon startup.

https://www.youtube.com/watch?v=UwM4OqsLek4

[Stocker]

^^ Interesting! I'm familiar with the typical 'roar' for a short time on cold start-up, but never knew exactly what caused it.

[Boog]

Does the truck currently have a direct drive fan or a fan clutch setup from a 350 truck? If it's a direct drive fan by all means install a clutch setup. Not only will it aide in engine warm up but will run quieter as it freewheels running down the road. Less drag from the fan equals more power and we all like that right?