I put a new Flex-a-lite fan clutch on my rig and notice now that when I start it cold the fan is running pretty high (I hear the roar) while cool for the first few minutes when cold. Then it goes away and I don't hear the roar any more. I am wondering if it is supposed to do this? When it is cool, shouldn't it be disengaged and be free spinning until it warms up since it is a themal type fan clutch? I am wondering if it is defective?

 

The fan clutch should engage at low idle speeds. The purpose is to pull air through the radiator. At high speeds(it doesn't know if it is running or not) it thinks that the air is being forced through the radiator.


So, it should disengage at high rpms.

That's about all the help I can be.

 

Thanks for the response JB. Anybody else notice that the fan roars when started from cold and then the roar goes away after about 3 minutes? it is definately the fan causing it, but I am wondering if the fan clutch is defective since it is thermally operated and shouldn't be engaged unless hot I would think--agreed it should be engaged at low rpm, but I thought the thermal part meant at low rpm when a certain temp is reached.

 

I think the clutch just works on temperature, not on engine speed. When they do the emissions check here in NC, they idle the engine up to a steady 2500 rpm for a couple minutes just prior to the test. After a minute or so, I can hear the fan engage. I don't know why it would come on when you first start the truck though. Can you turn the fan by hand with the truck off?

 

Clutch is temp. controlled. A bi-metal coiled sping engages and dis-engages clutch with temp. change. The clutch has more drag on it when it is cold though.

 

Yeah, I can turn it by hand, when it is cold, but there is some resistance when I do it.

When you say there is more drag on it when cold, does that mean it runs more when cold?

 

There is a viscous fluid in the clutch - when this fluid is cold it won't allow the fan to free wheel so it turns. Every one of my vehicles roars when cold, until it warms up enough that the fluid in the clutch lets the fan free wheel.

What you are hearing is normal.

 

Is there a break in on these? seems like this will delay my engine warming up since the fan is blowing cold air on the engine/radiator??

 

Not if the thermostat is working right. It should keep coolant from going through the radiator until it gets hot anyway. Older cars/trucks didn't even have a fan clutch, the fan just ran full force all the time.

 

From what I have read in other threads, the fan clutch is triggered to "clutch" the shaft when there is sufficient engine heat to heat up the viscous fluid, thus turning the fan faster and pulling in more air through the radiator to cause cooling. That makes sense to me.

But I have also read that it is normal for the fan to "roar" at cold startup for about a minute, then quiet down...otherwise the clutch may be bad. This would mean the fan clutch is "clutching" when engine cold-> opposite of what I would think. How could this work if the viscous fluid is cold, and why would a cold engine need cooling?

Can any more mechanically inclined FTE'ers set me straight?

 

The viscous fluid itself needs to warm up by it's own friction to do what it needs to engage/release the fan. It takes a minute or two for this to happen, so it engages. Apparently it doesn't negatively impact the heating/cooling since the tstat is closed anyway. After a few minutes everything is operating as it should with the clutch.

I just put a new clutch in and noticed this right off. My old one wasn't bad as in causing overheating, but they wear over time and I don't recall hearing the roaring very much when I started with the old one.

 

i had to replace a clutch fan in another vehicle due to overheating and put a heavy duty one in it everytime i started up it would roar for the first 30 to a min on a cold start