Fan clutch? Maybe?

[Jeremy_5]

Lately my truck has been running to hot while idling. As long as I am driving it is fine, but if I have to sit at a stop light for a while the temp will rise fairly quickly. I was thinking it might be the fan clutch, does that sound possible? Should you be able to grab ahold of the fan and move it relativly easy, becuase mine is really hard to turn.

Also, an explanation of what a fan clutch does would also be appreciated ( I want to make sure I have it correct).

[71-longbed]

its my understanding that the clutch disengages at higher rpms(aka more air is being forced in rad) and the clutch grabs more at idle (where less air being pulled into the rad.) .. i might be wrong so dont quote me

[Stocker]

It should be somewhat hard to turn by hand, gooey feeling as if it's turning in molasses. Wish I could find a good website to explain it better...

Some use a temperature-sensative silicon fluid which gets thicker (more viscous) as it gets hotter, causing the clutch to engage and turn the fan. Some have an external bimetal spring that acts on the clutch, though I'm unsure if they also have fluid inside.

This design allows use of a very aggressive fan, capable of pulling a lot of air when necessary - but it can turn much more slowly (not actually free-wheeling) when additional cooling is not required, thus saving fuel, robbing less power, and making less noise.

Back to yours - if it turns hard by hand, and sounds like it's pulling a lot of air, it's likely doing its job. Since you don't run hot on the highway, your radiator, thermostat, and hoses should be good. Do you have a fan shroud? If not, the fan isn't pulling much air through the raditor in traffic, though at speed, enough will come through the grill to keep things cool.

[flip66]

this could be wrong but I have heard and seen it done, if you let the car get to operating temp or above is when the clutch kicks in. If you take a rag or towl and slowly lower it into the fan you will be able to stop the fan if the clutch is bad. If the fan does not slow down the clutch is working right. be carefule because if it is good it can do some damage

[Jeremy_5]

Thanks for the replies so far. Stocker thanks for the explanation it helped. But as far as the problem it must be something to do with the fan, and yes I have a fan shroud, I will try to check it out more thouroughly tomorrow. It needs its coolant changed, seems like more water than coolant could that have anything to do with it? I wouldn't think so, if that was the case it should run hot all the time. right?

[1-PU70]

I dont know about sticking a rag in the fan when the motor is running but what I would do is let the motor get hot like you said when your waiting for a light. Shut the motor off and then try to turn the fan by hand. If its working it should be harder to turn.

[Stocker]

Fresh coolant (30% to 50% antifreeze) might help, but I wouldn't think that's your problem. If you believe it's the fan, instead of spending the bucks for an aftermarket unit, try a junkyard. Look for one from a large late-model car, van, or truck - it'll probably be a more heavy-duty unit. One more possibility, though likely a long shot... Some fan clutches can be taken apart, and the fluid inside replaced. Mine is like that - it failed once, many years ago, and I found it was like a sandwich, with a front and a rear half, bolted together. I got a small vial of fluid at a Toyota dealership, and voila! No problems since!

[smitty62]

DON"T stick a rag or anything else in the fan! SCHHEEEZ!

[flip66]

I did not think it was that safe but I had seen it done.

[franko72]

I would change the thermostat ,and flush and fill the radiator before I messed with the clutch fan.Dont top off the coolant level all the way to the rad. neck opening .It should be full at a couple of inches down.How many core rows are in your radiator? Maybe you could increase to a 3 or 4 row Radiator.

[Stocker]

Originally Posted by franko72

Dont top off the coolant level all the way to the rad. neck opening .It should be full at a couple of inches down.

Yeah, if there's no overflow tank - you can fill it but it'll just puke out the top inch or so. With a tank, you fill to the top, and of course use a sealed-system cap.