Fan not spinning

[theanimal]

Ok guys. Please forgive my lack of knowledge on this truck but I just took possession of it and don't know a ton about it. Anyways is the fan on the engine supposed to spin all the time? Today my temp gauge was showing about 190, there was coolant dripping from the overflow hose on the tank and the fan isn't spinning at all. Do I need a new clutch for the fan? If so is that something I could get from the local cummins dealer? Thanks for your patience guys'. By the way it's a 90' m923a2

 

[brasco]

Hmmm.... mine will only come on when it gets put under load. I can drive it around town or down the interstate and it never comes on. It will come on when going slow off-road up a hill and even then only for a minute or less.

I had a bad fan clutch once and the failure mode made the clutch stay on all the time - the fan clutch was toast and I bought a used one from a member here. The fact that it is not running is good in my opinion. This is expensive to replace.

The other part that can fail is the shutter stat. You can search this site to learn how to test etc.

I have found parts a http://comfortairgr.com

You probably don't have anything wrong but it is good to learn about.

 

[todds112]

There is an air activated clutch on the fan. When the coolant gets to 190 degrees (I think there are 200 degree ones too) the Shutter Stat (mounted in the metal radiator hose on the upper left side of the radiator) should open and allow air pressure to the clutch engaging it. Failure points could be bad shutter stat, bad fan clutch, or clogged air lines between the 2. Apparently there is an elbow where the air line goes to the fan clutch. There is a little screen in the elbow that can get clogged with debris. Shutter stats failing is a pretty common issue too. Sometimes they can be cleaned and O-rings replaced to get them going again. Hopefully its not your fan clutch itself, they are scary pricey.

 

[Floridianson]

Here is one of the threads about shutter stats and fan clutches. My last post gives some info as to the fans and shutter stats. Yes on the 5 ton 939 series the fan should be spinning free when motor not running or if it has not got above the shutter stat opening temp. So to check if the fan clutch is working without air it should spin free and when you apply air from an outside source it should lock up. Most problems come from the shutter stat not closing or not opening.http://www.steelsoldiers.com/showthread.php?136931-Cummins-8-3-fan-shutter-stat

 

[theanimal]

Ok so this makes me feel a little better. Thanks for the info guys. I am trying to go though the tech manual but man it's a huge book of stuff I have to learn. It scared me when I didn't see it turning and even more when I saw the Coolant dripping. I will do some reading and try to learn what makes this beast tick. Thanks again

 

[brasco]

The coolant being forced out of the expansion tank is normal too if it is filled all the way up. Mine seems to be happy a little under half full. Any more than that then it just gets pushed out.

 

[m16ty]

All the fan clutches I've seen that broke where the fan wouldn't come on, the clutch leaked air like crazy. So I'd say if you clutch itself isn't leaking air, your fan clutch is probably ok.

It's easy enough to test though. As has already been said, remove the air line going to the clutch and apply shop air. If the fan engages when you pressurize the line, the clutch is ok.

 

[Swamp Donkey]

there was coolant dripping from the overflow hose on the tank

Does the coolant run out even after you shut the engine off? If the coolant side O-ring in the shutterstat fails it can pressurize the coolant system, causing this symptom. I would check this out first.

Remove the cap on the overflow tank and start truck. When the air reaches operating pressure, shut engine off and check for bubbles in the overflow tank. This can be done without disassembling anything.

To test the fan clutch, drain air tanks of all pressure. Remove the line on the shutterstat between it and the fan clutch. This will be a JIC type fitting. Remove the fitting that is left in the shutterstat and screw it back in to the line. This will give you an 1/8" NPT fitting to apply shop air to, which will be easier to connect with than JIC. Air pressure engages the clutch.

 

[theanimal]

Man yall are awesome. I will work on all of this over the weekend and let you guys know what I come up with. So far though I can tell you that no air comes out of the clutch at all and as for the coolant drip, I don't know if it drips while it is turned off as I didn't pay attention to that. I don't think it does though. Thanks again for the help.

 

[theanimal]

I just wanted to give an update on the whole fan problem. Turns out there is no problem at all and Im just paranoid. After the temp finally got to 190 the fan came on and ran just fine. This is good with me because I have enough stuff to work on. Thanks for the help everyone.

 

[73m819]

For FURTHER peace of mind, I would READ the -10 (operators manual) if I was you.

 

[swbradley1]

Thank you for the update, frequently no one ever hears the issue has been resolved.

 

[73m819]

I know the first time the fan came on in a 939 truck I was driving, I thought something broke due to the NEW SUDDEN high noise level, took me a minute to get over the "OH CHIT" moment.