How to check if fan clutch is good/bad? [Archive]

View Full Version : How to check if fan clutch is good/bad?

Nick

07-22-2009, 11:48 AM

I've always heard that if you can spin it, it's good. If it doesn't spin, no good.

I can MOVE mine, but it does not spin freely, if I try to spin it it'll move a blade or two and stop. There's quite a bit of resistance. Is that normal?

I'm doing tune-up stuff and I'm wondering if it needs attention 'cuz it seems like an easy fix. Thanks!

4x4mike

07-22-2009, 12:37 PM

I replaced the one on my old truck but it turned out it didn't need it. It was a Toyota but it was the same idea. Basically when it is "cold" or cool there should be resistance and when it's warm it should move more. I have been in vehicles before when they are not working. Basically when you accelerate the fan gets really loud. When I replaced my there was little to no difference between the brand new factory one and the 16 year old one that I imagine was original.

Do you think it's going bad just because you thought to check it so you tried to spin it? If so it's probably fine. If it's really loud and/or you're running high temps it might be worth checking.

Lee

07-22-2009, 01:41 PM

if you have a bunch of miles on it, just swap it out. its not that expensive and it takes about 20 minutes to change out :)

MTL_4runner

07-22-2009, 03:31 PM

Nick

07-22-2009, 03:53 PM

Thanks a lot everyone - seems that it's good and I need not worry. It's a '96 but only has 83K on it, so it should be fine.

It does have less resistance when warm. There's a wire up on changing it out around here and it seems very simple, but if it aint broke...

Do you think it's going bad just because you thought to check it so you tried to spin it? If so it's probably fine. If it's really loud and/or you're running high temps it might be worth checking.

I was simply going over the tune-up stuff and though to check it. I didn't have any overheating...other than my 4Runner sounding like a jet engine at cold start up (normal) , I hear no unusual noises.

Lee

07-22-2009, 07:47 PM

my 01's fan clutch went around 90K or so. i replaced hoses, the radiator, the thermostat in pursuit of what was overheating my engine because i was consistently told that the way my fan clutch responded to spins was normal....

20 minutes to swap it out and was so mad at myself for wasting so much time and effort swapping out other things :laugh:

just keep it in mind if you see signs of overheating.

slosurfer

07-22-2009, 10:14 PM

If it is a oem fan, they are uber easy to rebuild. You can even switch to a thicker silicone fluid for more cooling if you need it.

mastacox

07-23-2009, 10:45 AM

Basically when it is "cold" or cool there should be resistance and when it's warm it should move more.

That's backwards. The fluid clutch is designed so that when the engine is cool there is less resistance than hot. That way when the engine is hot the fan spins at or close to the engine speed, but when it's cool the fan spins slower than the engine. It's a self-adjusting temperature control mechanism to make sure you're pulling more air when the engine is hot.

MTL_4runner

07-25-2009, 08:31 AM

The fan clutch is a bit confusing because it's a viscous (silicone fluid filled) design. So when the fluid is cold it does have more resistance than when it is warm (hence the jet engine sound when the engine first fires up, then the sound goes away after the fluid is warm). The second piece of the puzzle is that there is a thermally activated mechanical spring (see attached pic) on the back of the fan which when hot enough will cause the fluid clutch to lock up.

The fan can go "bad" by either leaking fluid (which causes it not to lock up properly and can be a source of overheating) or the thermal spring may mafunction (causing the fan to be always locked and can be a source of poor gas mileage).

Here's a good link for checking the fan clutch operation and topping up the fluid:
http://www.offroad80s.com/how-to-top-up-your-fan-clutch-and-do-the-blue-fan-clutch-mod-t1160.html