Fan Clutch Engaged on Start-up

7208 Views 23 Replies 14 Participants Last post by Bcataldi001, 10 mo ago

Kschill24

Discussion Starter · Jan 15, 2021

Hello all,
Since I've had my truck, every cold start has begun with the engine fan blowing at full bore, sounding like a semi truck. After about 30 seconds the fan will idle down with the engine and the noise will go away.

I brought it into my auto-tech class today and both my instructors were perplexed on why it was happening and ended up telling me "its just the way it is." There doesn't seem to be anything wrong with the fan clutch but it always goes full bore when its not warmed up (in the hot summer or below 0, it always does it on startup).

My question is - will replacing the fan clutch fix this loud startup? One of my buddy has a 2011 frontier and does not have this problem so i'm not quite bought on the "its just how it is" explanation.

Has this happened to anyone else and did you fix it?

Thank you, your experience or advice would be greatly appreciated

1 - 20 of 24 Posts

CT_Nismo

· #2 · Jan 16, 2021

As I recall, the fan clutch is temperature activated. A cold start should not engage the fan. Very strange.

Try this: With a cold engine, try to spin the fan by hand. It should freewheel. If you cannot spin it, something is wrong with it.

Reactions: 1

Skibane

· #3 · Jan 16, 2021

It's normal.

The clutch has a "viscous" fluid inside it that's thicker and stickier when cold.

The extra thickness makes it more efficient at coupling the engine fan pully with the fan.

After a few seconds of operation, slippage in the fluid warms it up, making it thinner.

Thinner fluid isn't as efficient at coupling the pully and fan - so the fan speed slows down.

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Reactions: 1

Kschill24

Discussion Starter · #4 · Jan 16, 2021

CT_Nismo said:
As I recall, the fan clutch is temperature activated. A cold start should not engage the fan. Very strange.

Try this: With a cold engine, try to spin the fan by hand. It should freewheel. If you cannot spin it, something is wrong with it.

Moves just the same as when its warm, not much resistance

Kschill24

Discussion Starter · #5 · Jan 16, 2021 (Edited)

Skibane said:
It's normal.

The clutch has a "viscous" fluid inside it that's thicker and stickier when cold.
The extra thickness makes it more efficient at coupling the engine fan pully with the fan.

After a few seconds of operation, slippage in the fluid warms it up, making it thinner.

Thinner fluid isn't as efficient at coupling the pully and fan - so the fan speed slows down.

View attachment 326268

Im sad to say you sold me on the "its just the way it is" explanation... Thank you!!

greenmachine

· #6 · Jan 16, 2021

My 2018 has done this since new. It’s random and doesn’t seem to matter what the temperature is. I don’t remember my 2008 doing this though.

Reactions: 1

SoCal

· #7 · Jan 16, 2021

Kschill24 said:
Hello all,
Since I've had my truck, every cold start has begun with the engine fan blowing at full bore, sounding like a semi truck. After about 30 seconds the fan will idle down with the engine and the noise will go away.

I brought it into my auto-tech class today and both my instructors were perplexed on why it was happening and ended up telling me "its just the way it is." There doesn't seem to be anything wrong with the fan clutch but it always goes full bore when its not warmed up (in the hot summer or below 0, it always does it on startup).

My question is - will replacing the fan clutch fix this loud startup? One of my buddy has a 2011 frontier and does not have this problem so i'm not quite bought on the "its just how it is" explanation.

Has this happened to anyone else and did you fix it?

Thank you, your experience or advice would be greatly appreciated

Maybe it does it when first started because the engine is running faster while warming up - so the fan spins faster. The clutch doesn’t completely disconnect the fan from the engine.

CT_Nismo

· #8 · Jan 16, 2021

Skibane said:
It's normal.

The clutch has a "viscous" fluid inside it that's thicker and stickier when cold.

The extra thickness makes it more efficient at coupling the engine fan pully with the fan.

After a few seconds of operation, slippage in the fluid warms it up, making it thinner.

Thinner fluid isn't as efficient at coupling the pully and fan - so the fan speed slows down.

View attachment 326268

Your explanation does not make sense. The fan should couple with the engine at elevated temperature; this is when cooling is needed.

Reactions: 2

RockMechanic

· #9 · Jan 16, 2021

Kschill24 said:
Hello all,
Since I've had my truck, every cold start has begun with the engine fan blowing at full bore, sounding like a semi truck. After about 30 seconds the fan will idle down with the engine and the noise will go away.

EDIT: most of this information is for Electrically controlled radiator fans, did not realize this is apparently a temperature controlled variant. This information may not be relevant.

This reminded me of something, but I could not remember what it was until now. We have a very old vent fan in the bathroom that does the same thing. (sounds like a damn jet taking off but then slows down and stops after less than 5 mins of running). I wonder if when your fan starts out cold everything inside is loose and as it heats up it slows down due to internal friction/heat. This would explain it's loud noise (due to being out of internal alignment). It may be the fan clutch, or the internal bearings on the fan, or even if its getting too much voltage or voltage changes during operation (I'd at least check it), but something I think is creating internal heat and slowly seizing up the fan, or like I said the power supplied may be to blame.

Does the fan speed back up when the engine is under load/hot? I know they are supposed to at a specific rpm, if not that may be the cause. I believe a multi meter can be used in order to detect a resistant force on a motor,( this is from my college days of many years past so bare with me). I do not remember exactly how, but I believe the resistance will spike as it heats up/encounters load if the load is significant it will do this abnormally fast. For all I remember this may as well be akin to voodoo magic.

Outside of that, If it appears to be working fine and speeding up as the engine is under load, it could be what I think it is. Outside of the noise as long as it's working you should be good.

Definitely something to look more into though.

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Reactions: 1

SoCal

· #10 · Jan 16, 2021

CT_Nismo said:
Your explanation does not make sense. The fan should couple with the engine at elevated temperature; this is when cooling is needed.

The fan still spins when the engine is cold - just not as fast as when the engine is warm.

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RamTest

· #11 · Jan 16, 2021 (Edited)

It depends on the state of the clutch when the engine is shut down. There's a thermo-spring on the front to open and close an internal valve releasing oil to engage or disengage the high speed mode of the fan.

If it was hot enough for the thermo-spring to open the valve before shutdown, or if the radiator was hot enough to open the valve after shutdown, the oil will fill the "clutch" vanes to engage high speed even with the motor off. As it cools the valve closes, but it takes centrifugal force to pump the oil out of the clutch. Starting cold will spin that oil out of the clutch in a few seconds, but for those few seconds it runs at high speed.

If you start cold, let the fan return to normal speed and then do a cold shutdown, when you restart again the fan will not run at high speed, as there is insufficient oil in the clutch, and the spring never got hot enough to open the valve.

Reactions: 2

CT_Nismo

· #12 · Jan 16, 2021

SoCal said:
The fan still spins when the engine is cold - just not as fast as when the engine is warm.

View attachment 326273

Yes, your post is my understanding on how fan clutches work. The situation with the OP is that his fan spins rapidly upon a cold startup. Some time later, after the engine has warmed a bit, the spinning goes down. I think this is strange.

Clint

· #13 · Jan 16, 2021

I had that happen on my last Titan 3 or 4 times without being able to pinpoint a particular reason whether first start or temperature outside etc. I know it was in the first 6 months approx and then never did it again whether here in NJ or in Florida but it never occurred again and had just under 60,000 miles at trade in. My thoughts were it was some type of thermostatically controlled spring. Some carburetor chokes had it done that way.
I wasn’t aware it was a fluid driven system and find it amazing how things are engineered.

Clint

Reactions: 1

bajasam

· #14 · Jan 16, 2021

I hope your not taking out student loans to attend this auto-tech school, as your getting ripped off if both your instructors have no knowledge about a cooling fan technology thats been the mainstream pick for close to seventy years.

Reactions: 1

RamTest

· #15 · Jan 16, 2021

bajasam said:
I hope your not taking out student loans to attend this auto-tech school, as your getting ripped off if both your instructors have no knowledge about a cooling fan technology thats been the mainstream pick for close to seventy years.

I disassembled one from a 1970 Cadillac just to see how it worked, that was around 1975. So they've been around at least 50 years.

Kschill24

Discussion Starter · #16 · Jan 16, 2021

bajasam said:
I hope your not taking out student loans to attend this auto-tech school, as your getting ripped off if both your instructors have no knowledge about a cooling fan technology thats been the mainstream pick for close to seventy years.

Its a highschool class. Free free free

RamTest

· #17 · Jan 16, 2021

Kschill24 said:
Since I've had my truck, every cold start has begun with the engine fan blowing at full bore, sounding like a semi truck. After about 30 seconds the fan will idle down with the engine and the noise will go away.

My 2017 has always done the same. Most clutch fans do.

Reactions: 1

Ryno_7

· #18 · Jan 16, 2021

My 2010 V6 almost never does this on start up, probably fewer than 10 times since I've owned it. Odd!

Kschill24

Discussion Starter · #19 · Jan 16, 2021

For those of you that have the same problem.... Is it this loud? Cant hear myself talk.

Reactions: 2

Clint

· #20 · Jan 16, 2021

Yes, mine was just like that on a rare occasion.

Clint

Reactions: 1

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