Thermo clutch fan

[Mettler]

My fan seems like it comes on at the wrong time. Does anyone else's fan come on at first start up and then every time I stop at a red light it comes on again. At start up the truck is cold so I would think that a fan would not be needed till the the vehicle is at normal operating temp. Is it me or is this normal?

 

[Maniak]

At first startup is normal. At stop from a red light, I don't "think" is normal..

If you sitting still, when the motor gets warm you should be able to hear the fan turn on.. Of if sitting still, bring the rpms up to 1500 or so, and after upwards of 5 minutes you should hear the fan turn off.

~Mark

 

[Willard]

It sounds right to me. Mine comes on at a red light. I can't hear it until I accelerate, but I know it's coming on.

Quick experiment. Go for a drive and get the truck good and hot. When you get home, pop the hood. You need to have access to the throttle for this, so you might need to remove the plastic cover protecting it. Open the throttle enough for the fan to disengage. Let off the throttle, after it sinks all the way into idle, you should be able to hear the fan clutch engage and the fan spin up. If it does then that means it's working fine.

 

[doonze]

Am I missing something? How do our fans "come on?", and how would you hear it?

Did some of these come with electric fans? Is this what we are talking about?

My fan is turning no matter what temp my truck is at, the clutch never "disengages", is my truck not acting right? These fan clutches never "free wheel" do they? I'm confused....

 

[Willard]

No, none of these came with electric fans.

They are all equipped with a thermostatic clutch fan. The clutch engages the fan based on engine speed and temperature. Under some conditions you can hear the fan roaring because this clutch is engaged most or all of the way. And the clutch never fully disengages, however it disengages enough to where the fan is turning only a small fraction of the engine speed. If you are not hearing your fan at all when it's hot, then it may mean you need a new clutch.

 

[Maniak]

^^^^ Exactly.. For example.. IIRC the Hayden severe duty fan clutch spins at 30% of shaft speed when it is disengaged and 90% when engaged. You can really hear the difference.

If your fan clutch is bad, you may not have near the same difference in speed so you may not hear it. It also means your not cooling as well as you can be, which may not be an issue, depending on where you live. Here in southern AZ, you "need" a good fan clutch.

~Mark

 

[doonze]

I'm sure my exhaust leak doesn't help either, I dont' know that I ever hear anything from the engine.

But I can tell you I've never noticed the fan, unless I was under the hood. Then it just turns same speed all the time from what I can tell.

Guess it's time of a new fan clutch? I did test it, turned off truck hot and spun the fan. After I let it go it moved about an inch then stopped. Was told that meant it was ok. Maybe not. Or maybe I just can't hear it.

 

[Mettler]

Okay so it sounds like my fan is perfectly healthy, just annoying. It robs sooo much horse power! And kills my mileage. Till it turns off. So what are some pros and cons of switching to an electric fan. My truck spends 98% of its life on the road.