Fan Clutch - Theory of Operation

[chengny]

As part of a thorough PM check, I discovered (I thought) that my stock Delco Remy fan clutch was not operating as per spec.

I came to this conclusion because at room temperature, while holding the driving hub in my left hand, I encountered some resistance to rotation while turning the fan clutch nousing with my right (hand). Ran it under hot water for several minutes, still no free wheel effect. Let it sit in the sink in hot water (130 F) for 15 minutes. Still a smooth roll, but nothing resembling a free wheel.

So, based on these admittedly crude tests, I had the kid go and pick up a good quality replacement clutch.

"Hey, lets feel the difference and I'll explain how this thing works", I told the boy.

Long story short; they feel exactly the same. I think that my original is functioing fine. At least as comapred to a brand new $91 unit.

Who can expalin why the clutch doesn't free up at higher temps? I won't bore everyone with the full story, but it involves the freezer, the oven and plenty of PB Blaster.

No matter what temperature I subject either clutch to, they both do not really change at all.

[merlin5577]

Originally Posted by chengny

As part of a thorough PM check, I discovered (I thought) that my stock Delco Remy fan clutch was not operating as per spec.

I came to this conclusion because at room temperature, while holding the driving hub in my left hand, I encountered some resistance to rotation while turning the fan clutch nousing with my right (hand). Ran it under hot water for several minutes, still no free wheel effect. Let it sit in the sink in hot water (130 F) for 15 minutes. Still a smooth roll, but nothing resembling a free wheel.

So, based on these admittedly crude tests, I had the kid go and pick up a good quality replacement clutch.

"Hey, lets feel the difference and I'll explain how this thing works", I told the boy.

Long story short; they feel exactly the same. I think that my original is functioing fine. At least as comapred to a brand new $91 unit.

Who can expalin why the clutch doesn't free up at higher temps? I won't bore everyone with the full story, but it involves the freezer, the oven and plenty of PB Blaster.

No matter what temperature I subject either clutch to, they both do not really change at all.

I dont know if I understand your question correctly, but I will give it a shot. The clutch is designed to stay engage at high temperature to cool the engine when its running at a higher temperature. At colder temperatures, the clutch disengages and allows the fan to "free spin".

Make sense?

[75K30]

Good call. Lets actually look at what the fan does. It draws air through the heat exchanger (radiator) right? Now, if the clutch were to disengage during higher temps, then the engine would overheat if the vehicle was not moving, because the fan would not be effective.
When the vehicle is cold, it does not require air to pass through the heat exchanger, so the drag can be minimized.

In theory the fan clutch is designed to reduce noise, and parasitic losses when the vehicle is at or below operating temps.
This clutch will never completely disengage, and will always drag. It will never freewheel, but will have less resistance when it has not reached its greatest resistance, and this is when the spring reaches its thermal or heated condition.

[merlin5577]

Originally Posted by 75K30

Good call. Lets actually look at what the fan does. It draws air through the heat exchanger (radiator) right? Now, if the clutch were to disengage during higher temps, then the engine would overheat if the vehicle was not moving, because the fan would not be effective.
When the vehicle is cold, it does not require air to pass through the heat exchanger, so the drag can be minimized.

In theory the fan clutch is designed to reduce noise, and parasitic losses when the vehicle is at or below operating temps.
This clutch will never completely disengage, and will always drag. It will never freewheel, but will have less resistance when it has not reached its greatest resistance, and this is when the spring reaches its thermal or heated condition.

Well if you want to be wordy about it........

J/K.

[75K30]

Originally Posted by merlin5577

Well if you want to be wordy about it........

J/K.

Thats how I roll......

[merlin5577]

Originally Posted by 75K30

Thats how I roll......

Yeah, Yeah, Yeah, we all know you and I both know our stuff..... you just use WAY more words to explains your stuff.....

[75K30]

Sometimes I use far too many words, this I know.

[merlin5577]

Originally Posted by 75K30

Sometimes I use far too many words, this I know.

Not a bad thing, better to be clear and precise, then risk leaving anything out.

[gmctrucks]

Good info after this write up I found go to-wards the bottom.
A fan clutch is a thermostatic device that exists as an integral component of certain automotive cooling systems. When the engine is cool or even at normal operating temperature, the fan clutch partially disengages the engine's mechanically-driven radiator cooling fan, generally located at the front of the water pump and driven by a belt and pulley connected to the engine's crankshaft. This saves power, since the engine does not have to fully drive the fan.
However, if engine temperature rises above the clutch's engagement temperature setting, the fan becomes fully engaged, thus drawing a higher volume of ambient air through the vehicle's radiator, which in turn serves to maintain or lower the engine coolant temperature to an acceptable level.
Most fan clutches are viscous or "fluid" couplings, combined with a bi-metallic sensory system similar to that in a thermostat.
Normally fan clutches are fairly reliable, but sometimes they fail. A common symptom of fan clutch failure is overheating at idle or in heavy traffic. Bad fan clutches can also cause poor performance of the car's air conditioning system because the fan also cools the air conditioner's condenser, which is directly in front of the radiator.
Another potential symptom of fan clutch failure (always drawing air at a high rate) in a cold weather climate is that the heating system blows lukewarm air never delivering sufficient hot air. (I found this info it's not my write up like 75K30 which already set us straight along with Merlin but I did find this because I knew there was two types of clutches.)
Fan Clutch Tutorial - Part 1 Good info.
Fan Clutches & Fan Blades Types of clutches.

http://www.mwrench.com/Whitepapers/FanClutchtest.pdf Testing clutch.

I still need to check my clutch like I wrote last week while stopped at a store on my trip to buy a soda pop & smoke a cig my temp went over 210 but once I got on the road it came down fast and my stat is one week old and I have always kept good antifreeze in my baby one has too with this TEXAS heat.

[75K30]

Now that was good info!!!