When does the clutch fan turn on?

Mmathw · Feb 24, 2018

On the way home today I was stuck in traffic and the engine got up to 225 degrees. Got home and left it idling and the Efan was on but not the clutch fan. I was under the impression the clutch fan was always on? If not when is it supposed to turn on? Also I did the ecu swap before this and drove it home since the directions say to drive and make sure the truck runs correctly. Not sure if that could have any effect on that? Thanks in advance

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WilliamS · Feb 24, 2018

Clutch fan should be on when the AC is running or when the engine reaches over normal operating temp.

Mmathw · Feb 25, 2018

WilliamS said:
Clutch fan should be on when the AC is running or when the engine reaches over normal operating temp.

Thanks!

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Wahrsuul · Feb 25, 2018

I was under the impression that the clutch fan is temp driven, it doen't have a connection to the engine. The AC fan comes on when the AC is on, but the clutch activates by temp alone.

muddy12 · Feb 25, 2018

If by “clutch fan”, you are referring to the one attached to the water pump pulley, then it should be spinning any time that the engine is running.
The clutch just allows the fan to spin slower than the engine when it’s cold. Once it reaches a set temp, it engages, and the fan then spins at the same speed as the engine.

If you have two electric fans, one is set to come on with the AC system, and the other turns on based on coolant temp.

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Mmathw · Feb 25, 2018

muddy12 said:
If by “clutch fan”, you are referring to the one attached to the water pump pulley, then it should be spinning any time that the engine is running.
The clutch just allows the fan to spin slower than the engine when it’s cold. Once it reaches a set temp, it engages, and the fan then spins at the same speed as the engine.

If you have two electric fans, one is set to come on with the AC system, and the other turns on based on coolant temp.

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Yeah that’s the one I’m talking about. I guess since mine wasn’t spinning I have a problem?

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Hemi395 · Feb 25, 2018

The clutch fan should be spinning when the engine is running it's just a question of how fast it's spinning which dependent on how high the under hood temp is. If the mechanical fan isn't spinning at Al when the engine is running you definitely have a bad fan clutch.

This is why a lot of guys go to the V6 efan because the Hemi mechanical fan is causing parasitic HP loss from the engine because it's always spinning.

DavidN · Feb 25, 2018

It’s a viscous operated clutch.
How it works is explained here:

When does the clutch fan turn on?

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