m939 fan clutch actuator

[Bolkbich]

The engine fans on my m939 trucks seem to be erratic. Sometimes they come on and go off pretty quickly. Other times they stay on for a long time, even with the temp below where it should shut off. On one truck if the fan comes on it wont go off untill i turn the truck off and leave it sit for a few minutes. Is there an air bleed on these fan actuators, so the fan comes on then goes off when the actuator bleeds off the air when the sender stops calling for the fan?

 

[steelsoldiers]

Sounds like you have an actuator or a fan clutch on the fritz. It should bleed off the air when the temp drops, which shuts off the fan. You could try shutting the truck off when the fan is running and the engine temp is below where the fan should be actuated. Then, undo the supply line that runs to the fan and see if it dumps air. If it does, then it would seem like the actuator is hanging up. If it doesn't, then it would seem like the clutch is hanging up. That's my way of thinking about this, but I don't currently own a truck to test out my theory.

 

[Bolkbich]

I think its the actuator. Im thinking it should bleed off the air from the supply line to the fan clutch. Unfortunatley thinking and knowing are 2 different things. I was hoping somebody had a concrete answer.

 

[trooper632]

where is the actuator located on this engine, the 8.3

 

[Bolkbich]

where is the actuator located on this engine, the 8.3

The upper radiator tube about 2 ft from the radiator.

 

[Scarecrow1]

Bolkbich after you turn your truck off is it still venting air from the actuator? Mine is and I can't find any info on if this is normal are not. Mine is a 250 Cummins so I am not sure if it is the same as yours but I will continue to search and if I find anything I will forward it on to you ...........

 

[Carlo]

I have problems with mine on the M923A2. It turns on late. I think it can be adjusted to turn on at lower temperture or higher. I have checked the TM and found little to nothing. Does anyone know how to adjust them?

 

[M35A2-AZ]

I do not think you can adjust them.
It should have the temp. it is set at stamped on the side of it.

 

[Carlo]

On the back it looks like something that would trun. I will get a photo and post it.

 

[Bolkbich]

Bolkbich after you turn your truck off is it still venting air from the actuator? Mine is and I can't find any info on if this is normal are not. Mine is a 250 Cummins so I am not sure if it is the same as yours but I will continue to search and if I find anything I will forward it on to you ...........

No my trucks dont leak air from the actuators after I turn them off. I get a burst of air when it turns the fan on ,but I dont hear any air when it disengages the fan. I think it bleeds it off slower.. I just hear the fan shut off.

 

[Carlo]

The M923A2 turns on slow as not with a burst. The M931A1 has never heated up enough to see it turn on! The old 250 runs allot cooler than the 8,3

 

[Carlo]

I am armed with new info. Im going out there today and see how mine is working. I will also look to see if a temp is stamped on the side. If so I think its true you cant adjust them.

 

[jdknech]

you can not adjust them, they are set for 195*.. but if you remove it from the truck, you can rebuild (clean) it on a workbench.. i just did mine yesterday.. use a spanner wrench to remove the end cap (CAREFUL, there is a small spring behind it.. dont lose it) inside there is a brass cup, with a brass plunger under it.. if you use a air gun on the ports, it comes right apart, if you clean it all up, and check for burr's.. then oil it with air tool oil, it should work good as new...

 

[Carlo]

I will give it a try! Thank you Sir.

 

[jdknech]

I will give it a try! Thank you Sir.

anytime.. let us know how it goes...

 

[jvero]

I will give it a try! Thank you Sir.

Did you ever get this figured out? I have the 8.3 and my fan is not coming on. I am not sure how to tell if it is the fan clutch or the air actuator. I will try to find the actuator and take it apart and clean it and see if the fan comes on after that.

 

[Carlo]

Well mine did work but I thought it was coming on at to high of a temp but it was not so high. The temp gage was off 15 degrees. I used a laser temp hand held to find out the real temp.
To check the clutch reverse the air lines at the actuator. If the fan runs it's the actuator that's not working. If the fan does not work then it's the clutch.
Verfify your gage is accurate first. How high does the gage read?

 

[jvero]

Well mine did work but I thought it was coming on at to high of a temp but it was not so high. The temp gage was off 15 degrees. I used a laser temp hand held to find out the real temp.
To check the clutch reverse the air lines at the actuator. If the fan runs it's the actuator that's not working. If the fan does not work then it's the clutch.
Verfify your gage is accurate first. How high does the gage read?

Thanks for your help! I had the truck out this weekend mostly idling and low rpm crusing through mud - about 800 rpms or so, never moving over a couple miles an hour. My gauge got as high as 230-240, but the truck showed no signs of overheating. I locked the fan in with the two docked bolts like it said to do in the manual, and after that the gauge read right in the middle at about 170ish and never really moved. I drove the truck home from GA to FL a week and a half ago (in relatively cool weather though) and I have made a few trips around town without the temp ever showing that high. I will try to get a laser temp gauge and check the temp, and maybe see if I can reverse those lines first to check the clutch. I do seem to have some moisture in the air system that I need to take care of also, not sure if that could affect the actuator or not. Thanks again!