Fan Clutch Delay

I have the NAPA ZJ fan clutch, I installed it approx 3 months ago. Here's the intermittent issue I have just recently noticed during cold starts. It seems that it doesn't engage when I first pull out of my driveway and then it engages about 100 feet down the road as the engine temperature rises. I haven't noticed this before, has anyone else run into this? Could it be time for a new fan clutch because this one may be faulty?

I believe that's the way they act normally.

I just installed a new fan clutch on mine, and the
instructions said that the clutch would not engage
upon initial startup.

vabeachtennis said:

I have the NAPA ZJ fan clutch, I installed it approx 3 months ago. Here's the intermittent issue I have just recently noticed during cold starts. It seems that it doesn't engage when I first pull out of my driveway and then it engages about 100 feet down the road as the engine temperature rises. I haven't noticed this before, has anyone else run into this? Could it be time for a new fan clutch because this one may be faulty?

Click to expand...

How could you tell when it engages? As far as I know, they spin all the time the engine is running,....slow when the engine is cold and faster when the engine is hot untill the engine cools down the it slows back down.
I remember driving a Chevy pickup 4 years ago, the fan will spin up really fast when the engine is started after it have been shut down for a few hours then it will slow down after about 30 seconds +/-. The roar of that fan was annoying to me.
I read here on this forum the % of speed of the fan blades verses the shaft speed engine cold verses engine hot. It was in one of the discussions about replacing the OEM XJ fan clutch with a ZJ fan clutch.
Yes, it is perfectly normal for the fan speed to increase when the engine is hot but unless you let the XJ idle a long time, I would think 100 feet is a short distance for the fan clutch to be fully engaged. I am driving a 1993 Toyota pickup now. After about 30 minutes in stop and go traffic I could hear the fan spinup really fast for a minute or two then I do not hear it anymore. From a cold start, I never did hear the fan for almost a mile and only in stop and go traffic on hot days.

One of these days I'm going to disassemble one of these
fan clutches to see exactly how they work.

The Hayden unit I installed a couple weeks ago had an info
sheet with it that stated the clutch ran the fan at between
30% to 70% of the pulley speed, depending on temperature.

I always figured a fan clutch would go from (almost) freewheeling
when cold to lockup when hot, but apparently that's not the case.

They use a heavy silicon "fluid" to engage. When cold, the fluid settles and causes the clutch to engage. After a few minutes it is distributed and the clutch disengages. Then when the temperature is hot enough, the bimetal spring opens the reservoir and allows the fluid to move, which causes it to engage again.

Here's some good reading http://www.peachparts.com/shopforum/showthread.php?t=67800

And you can tell when the HD fan clutch is engaged. It's kinda loud.

techno1154 said:

How could you tell when it engages? As far as I know, they spin all the time the engine is running,....slow when the engine is cold and faster when the engine is hot untill the engine cools down the it slows back down.
I remember driving a Chevy pickup 4 years ago, the fan will spin up really fast when the engine is started after it have been shut down for a few hours then it will slow down after about 30 seconds +/-. The roar of that fan was annoying to me.
I read here on this forum the % of speed of the fan blades verses the shaft speed engine cold verses engine hot. It was in one of the discussions about replacing the OEM XJ fan clutch with a ZJ fan clutch.
Yes, it is perfectly normal for the fan speed to increase when the engine is hot but unless you let the XJ idle a long time, I would think 100 feet is a short distance for the fan clutch to be fully engaged. I am driving a 1993 Toyota pickup now. After about 30 minutes in stop and go traffic I could hear the fan spinup really fast for a minute or two then I do not hear it anymore. From a cold start, I never did hear the fan for almost a mile and only in stop and go traffic on hot days.

Click to expand...

When it wasn't engaged, I could hear the engine noise, when it engages I can hear that loud assed fan noise.