New Guy Question - 5 ton Models M923, 925, 931, etc. - Re: Engine Cooling fan

[fredster67a]

Hey,
Quick question about the videos I see on gov Liquidation of the engines running on the various 5 ton models - sometimes I see the cooling fans moving and sometimes I do not,. Does this indicate a problem with the cooling fan assembly or some other system on the vehicle? Thanks in advance for any advice you can offer.

 

[GHall]

The fan clutch kicks on and off at a certain temp.. There is an emergency bolt to lock up the fan to where it spins all the time if the clutch goes out.

 

[fredster67a]

Gray, Thanks for yor response. Does this mean that the fan clutch will not kick in until the truck engine reaches a certain operating temeperature - so the engines I viewed may have been recently started? Thanks.

Fred

 

[GHall]

Fred,

Yes sir, the chances are that they were just recently fired up. These trucks take a while to warm up all the way. When the engines got hot enough the fan kicks on and you can generally hear it pulling a lot more air.

 

[juanprado]

Hi Fred,

Welcome! Gray's advise is correct on the fan lock out but it is only for the nhc250 a0 or a1 models. The a2 uses a different motor 8.3L that uses a different clutch with out the lock out feature.

Note, It is "possible" that the fan clutch or air operated actuator is not working properly. You would have to get the truck to operating temp to be sure.

 

[GHall]

Hi Fred,

Welcome! Gray's advise is correct on the fan lock out but it is only for the nhc250 a0 or a1 models. The a2 uses a different motor 8.3L that uses a different clutch with out the lock out feature.

Note, It is "possible" that the fan clutch or air operated actuator is not working properly. You would have to get the truck to operating temp to be sure.

Juan is absolutely right, I apologize for not differentiating between the two motors. I was speaking of the NHC-250, I have no experience with the 8.3..

 

[Trailboss]

Trouble is, you won't know if the fan clutch is not working until the engine overheats, like mine did. The bolts were made available for the fan lock for a reason. My problem was that the truck I picked up had to be jump started, so I couldn't shut the engine down to install the bolts since I couldn't restart it! As long as it was rolling the temps were OK, but if you stopped the temp started climbing. Just another recovery challenge to anticipate.

 

[crasheej]

They will start down hill with out to much of a problem.

 

[doghead]

You could push a 939 series truck for 5 miles downhill, and it still won't push start.

 

[PLP]

I have a few m939's with Cummins 250 on one of them the fan would barely turn when cold, the other two trucks the fan will spin fast when cold. I think the problem with the first truck is the shutter fan switch which is operated by air to control fan is malfuntioning. It appears If the fan shutter switch is working properly on the Cummins 250 the fan will spin fast at any temp, maybe just faster when hot. I can't speak for the Cummins 8.3 but all the GL videos i see the fan is either stopped or barely spinning.

 

[Stryker100]

My m923a1 has a slow fan at start up. Just got her home last night, So have yet to warm her up. Will be watching this thread and Adding when i see what mine does. Stryker