How to test a fan clutch?

[Dapplecreek]

My bus has a Cummins 5.9 engine, which recently threw an over-temp alarm on a fairly short hill. I pulled over and idled for awhile, which brought the temp down to 240 degrees (apparently its normal operating temperature). I wonder if my fan clutch is working properly. This is important to me because I want to cross the Rockies in a couple of weeks.

How does one test one's fan clutch? Gently try to jam a rolled-up magazine in the blades of the fan when the engine is up to full temperature?

My thought is that if one can stop the fan then the fan clutch is not working properly. Thus the clutch or the sensor or the wires or something is bad in that system. If one gets confetti from the end of the rolled-up magazine and the fan keeps spinning with enthusiasm, then that isn't the problem. Might be a plugged radiator or something. Right?

Any other thoughts would be welcome. There are no leaks and the fluid is green. I have an IR thermometer if that would assist in the diagnosis.

[alpine44]

Originally Posted by Dapplecreek

My bus has a Cummins 5.9 engine, which recently threw an over-temp alarm on a fairly short hill. I pulled over and idled for awhile, which brought the temp down to 240 degrees (apparently its normal operating temperature). I wonder if my fan clutch is working properly. This is important to me because I want to cross the Rockies in a couple of weeks.

How does one test one's fan clutch? Gently try to jam a rolled-up magazine in the blades of the fan when the engine is up to full temperature?

My thought is that if one can stop the fan then the fan clutch is not working properly. Thus the clutch or the sensor or the wires or something is bad in that system. If one gets confetti from the end of the rolled-up magazine and the fan keeps spinning with enthusiasm, then that isn't the problem. Might be a plugged radiator or something. Right?

Any other thoughts would be welcome. There are no leaks and the fluid is green. I have an IR thermometer if that would assist in the diagnosis.

There are two type of fan clutch systems. One has a bi-metal temperature sensor on the clutch housing, the other is externally controlled. Both systems need to get your attention when the fan kicks in. A clutch with the built in bi-metal thermostat cycles a little softer but you may have heard the fan sound big rig trucks make when they pull into a truck stop. The HMMWV for example has a clutch that is hydraulically actuated and controlled by an external valve and thermostat. When that fan kicks in for the first time you hear it you'll think the engine is just coming apart on you. Long story short, a well working engine-driven cooling fan is making substantial noise in a truck, bus, etc. If it doesn't make noise, it's not working.

[Mgulley82]

Don’t do the magazine thing

Can you spin the fan by hand with the engine off and cold?

[cadillackid]

alpine has it right... there are 2 types..



the viscous fan clutch has a minimum speed.. when the engine is running your fan will be turning at a nominal speed.. say 300-400 RPM and will be moving some air but not a ton.. when thje engine is dead cold, your viscous clutch should engage fully wit ha good fan roar foe the first minute or so you operate.. then the fan sound will slowly fade over a few second time frame and the fan disengages to its minimum speed. these clutches will have varying amounts of resistance when the engine is turned off.. when running they are controlled by thermostat that measures the air temp from the radiator.. low coolant will make these malfunction, as will defective clutch... sometimes you can adjust them.. here is the pic of the nose of a viscous clutch showing that bi-metal thermostat.







an electric or air fan clutch will hace a very slow off speed.. and will likely have a wire harness or air line going to the hub on the engine near the fan..



this is what an electric clutch looks like. when the engine is off that fan has zero resistance and is completely free..








-Christopher

[Mgulley82]

I could be wrong

But my understanding of my air fan clutch is with no air pressure it is fully engaged

Meaning

With engine off it shouldn’t spin freely - this would be evidence of a worn lining

[Brad_SwiftFur]

Originally Posted by Dapplecreek

My bus has a Cummins 5.9 engine, which recently threw an over-temp alarm on a fairly short hill. I pulled over and idled for awhile, which brought the temp down to 240 degrees (apparently its normal operating temperature).

As a general rule, 240 degrees is *WAY* overheated/ruined engine territory. However, since (I am assuming) yours has been running for considerable time at that reading, I will assume your engine is not blown. I would suspect, however, you may not be getting an accurate reading. I would check the actual temp when it's warmed up, which should be in the 180-195 range. A failed sensor could be the culprit, or the gauge or wiring.


Given that you had an over-temp alarm which didn't sound until you went up a hill, that supports my thought that your engine is not running excessively hot. I would still check it's actual temp and make sure the gauge reflects correctly. There's a few likely causes for the over-temp event:


1. As noted by others, the fan isn't engaging to full speed when needed.
2. The radiator fins could be clogged with dirt and debris. Carefully blow out from behind (can also use pressure washer, be *VERY CAREFUL* not to bend the fins)
3. Low coolant/poor circulation/failing water pump (unlikely in your case, but included for completeness)
4. Inadequate cooling system (highly unlikely in your case, this would apply if the engine has been modified for much higher power without regards to the extra heat it will produce)

[Dapplecreek]

Update:

I didn't to the magazine trick, but instead used a half-used roll of paper towels (didn't see the replies above until afterwards, sigh).

The engine went to 240 degrees while idling (clue #1 that we have a problem).

The fan could be stopped by gently letting the fan blades whack the edge of the paper towel roll. It tore the corner off the roll, but stopped the blade without much difficulty. No roar of fan could be heard, either - though the temp and the ability to stop the fan kinda tells the story.

I am sourcing the clutch right now and I have a truck shop that can see me tomorrow at noon. Yay!

Thanks, all!

[cadillackid]

so which clutch do you have? the kind with the coil in front or the electric type? if you have the electric type and get no engagem,ent, its worth checking the wiring to make sure its getting power applied to it..



if its the viscous type then check with Kit-masters, thats who i source all things viscous clutch from and they will likely have one to fit your freightliner..
-Christopher

[turf]

overheating at idle sounds like a tstat or water pump to me.

either will be cheaper than the fanclutch

[Brad_SwiftFur]

Originally Posted by Dapplecreek

Update:

The engine went to 240 degrees while idling (clue #1 that we have a problem).

Not necessarily, there is a thermostat for a reason, it should warm up even when idling.

Originally Posted by Dapplecreek

The fan could be stopped by gently letting the fan blades whack the edge of the paper towel roll. It tore the corner off the roll, but stopped the blade without much difficulty. No roar of fan could be heard, either - though the temp and the ability to stop the fan kinda tells the story.

The fan should still be free even when warmed up. Usually there is a threshold temperature at which it should engage fully, and just idling with the fan turning a little, the engine may not reach this threshold. My bus has the viscous coupling type fan clutch and when I'm going down the road, it occasionally kicks in, and there is a very obvious rush of air that goes with it. As it cools, the fan disengages and goes back to turning just a bit. I've driven trucks with the electric clutch and there is sometimes a belt chirp as the fan engages (fairly common when idling with the A/C on, it needs to cool the condenser moreso than the coolant).


A viscous fan clutch can (and should) be checked with the engine off - it should turn, but with some resistance. The warmer the clutch (or, more correctly, the bimetal spring), the more resistance it should have. If it turns very freely, check to see if there's signs the viscous fluid has leaked out. An electric clutch can be checked with the engine off as well, just put 12 volts across it and the fan should turn with the belt (IE, with the engine off, it should not turn at all).


I *DO NOT* recommend fan testing with the engine running. Be safe out there.

[Dapplecreek]

Well, I have the proper fan clutch arriving by UPS tomorrow ($312), and an appointment with a for-reals truck mechanic tomorrow afternoon. We'll see where it goes. Yes, I have been a bit hasty with my diagnostics, but we need to be on the road. I will let you know what the mechanic finds.

Thanks, all!

[o1marc]

240° is not a good "normal" operating temp. I suspect a faulty guage or you have other cooling issues. Anything over 230° starts to concern me.

Posted this after reading your first reply today, before reading all the others, so your issues are being addressed.

[Dapplecreek]

This shows how little force it took to stop the fan with the engine at 240 degrees:

I sure hope it was the fan clutch: $330 is not a trivial amount to throw around. But tomorrow the bus will be in the hands of a fellow who knows what he's doing, so we'll likely get things working properly.

[Dapplecreek]

... I suspect a faulty gauge...

Next time I have it running I will use my handy-dandy IR non-contact thermometer to see what the radiator and hoses show in comparison to the dash gauge.

[Gdog 5651]

I cannot think of a time or place (bowels of hell maybe) where I could get a 5.9 Cummins to 200 degrees at an idle much less 240 if that temp is correct more than the fan clutch needs to be looked at Gene

[Dapplecreek]

Originally Posted by Gdog 5651

I cannot think of a time or place (bowels of hell maybe) where I could get a 5.9 Cummins to 200 degrees at an idle much less 240 if that temp is correct more than the fan clutch needs to be looked at Gene

Sad to hear that. I'll check the temp with the IR thermometer tonight to verify the gauge. But the bus will be in the hands of a truck mechanic tomorrow with instructions to vet the cooling system. And I'm sure glad to be doing that before leaving my home on the cross-country move!

[Dapplecreek]

Originally Posted by Gdog 5651

I cannot think of a time or place (bowels of hell maybe) where I could get a 5.9 Cummins to 200 degrees at an idle much less 240...

Maybe in Texas?