Wrong replacement engine fan...

[Coffey1]

Correct

 

[Awesomeness]

The dumbest engineer got to design this fan with rubber it's useless other than destroying your own truck.

Many/most of the trucks still have the old fan. I know you're upset yours broke, but if it was actually as bad a design as you suggest, they would have replaced them all long ago, like the driveshafts.

 

[Coffey1]

Well you know are government they aren't the quickest or the smartest bunch especially if it cost money they can't put in their pockets.

But like I said if your so in love with the rubber keep it ! I am not forcing you to remove it.

 

[Awesomeness]

Well you know are government they aren't the quickest or the smartest bunch especially if it cost money they can't put in their pockets.

But like I said if your so in love with the rubber keep it ! I am not forcing you to remove it.

I didn't say I loved it. I'm just saying your theory is shallow. And I don't want newcomers to think there is actually some history or evidence behind it.

There are many equally-good reasons they changed the fan.

• Maybe they needed to change the clutch to a larger one, that no longer fit the original fan, and the fan had to change too.
• Maybe there were supply issues and some part of the clutch/fan system was no longer available.
• Maybe the original fan had to have the rubber grommet because there was a wide tolerance on how balanced it was, but later they were able to make a more balanced fan that didn't need it anymore.
• Maybe the cooling capacity was updated and they needed to change the blade pitch of the fan, and the new thinner fan didn't need to be spaced out as far anymore.
• Maybe there was an old specification requirement or standard that required a certain amount of clearance around the fan historically, and the engineers didn't like the rubber grommet but had to have it, and then the requirement was updated and they could remove it. For example, maybe it needed to be able to clear some A/C compressor or accessory pump available at the time.

We just have no idea. Nothing in these military designs is done unintentionally - trust me. It all goes through tons of design, review, testing, analysis, redesign, and improvement before it ever makes it to production. When there have been actual problems with the trucks, the military has been quick to pull them out of service and fix them. So the fact that many/most of the trucks still have the original grommet-style fan points to Uncle Sam not being concerned about the fan failing.

 

[Coffey1]

So I guess they found a way to age the rubber to see if it would fail after truck sits or heated and cooled for several years

And you also have a lot of maybes
I for one will remove and bolt every fan I come across because it's no fun leaving a truck where it failed.

It's almost like you were one of the designers the way your trying to defend it.

 

[Coffey1]

And your absolutely wrong they sure as hell don't fix things until people start dying.
The 939 is a example
And I can't swear but I bet several injuries to the drive shaft problems

 

[Awesomeness]

And you also have a lot of maybes

Thank you for pointing that out to everyone. This is the difference between what you and I are saying, and what I want people who read this thread in the future to get out of it. I'm making it clear my ideas are just speculation, and you're portraying your opinions as facts.

 

[JD4044M]

All this talk about fans 700.00 parts ect to solve the problem a fan is pretty much a fan not all fans use rubber and not all fans are military specs to use. Part I don't understand why not a After Market Fan. I do know if my fan is defective I am not spending 700.00 for a military approved fan blade. Take this fan it is a solid center close to what the original blade is except a more modern blade design. Seems like if it is the right diameter this one is 32" but there are lots of them out there why would it not work bolted to a old style clutch. Hard for me to say for sure till my truck is here to look at it and see. They have steel blades to it only moves air? Can't see why another set up could not be used? At least a new fan blade would be now new not new old stock new?

Horton Fan Blade

 

[Awesomeness]

All this talk about fans 700.00 parts ect to solve the problem a fan is pretty much a fan not all fans use rubber and not all fans are military specs to use. Part I don't understand why not a After Market Fan. I do know if my fan is defective I am not spending 700.00 for a military approved fan blade. Take this fan it is a solid center close to what the original blade is except a more modern blade design. Seems like if it is the right diameter this one is 32" but there are lots of them out there why would it not work bolted to a old style clutch. Hard for me to say for sure till my truck is here to look at it and see. They have steel blades to it only moves air? Can't see why another set up could not be used? At least a new fan blade would be now new not new old stock new?

Horton Fan Blade
View attachment 811077

I have a few thoughts...

• You can pick up the military fans, both old and new style, for <$150 surplus. I'm not too concerned about a NOS fan, as it's made out of hard plastic and metal, so age shouldn't really affect it much.
• The military fan is special because it moves a TON of air. According to one of the engineering papers, it takes 26kW (35HP) to run the fan! You're going to have trouble finding cooling power like that in the civilian products, I think.
• However, do you need that much cooling power? Probably not. If you're ok with downgrading the truck's capabilities, you could use something less powerful, since you're unlikely to be hauling max load, with a trailer, in the desert heat. Up to you.
• Modern blade design would be nice, because the military fan sounds like a freight train when it kicks on.

EDIT: Correction to HP requirement of fan.

 

[Coffey1]

Unless parts have been left where they are exposed to crap they shouldn't be exposed to .

And if it was one fan I would be with awesomeness but I know of at least 4 that have failed.


The new clutch design doesn't have rubber and is directly bolted on

So what does that tell you

 

[JD4044M]

My fan in my Freightliner even on wildfires slow going on hills etc would only come on once in a while on a Cat 3406C loaded to 48,000 lbs GVW. You knew when it came on too it was loud. Seem like if it uses 57 HP which is a lot and hardly comes on less HP and more fan use might be better? I am sure the Military used the worst conditions to figure out the needed fans CFPM of air moved. Having 57 more HP sound pretty good to me?

 

[Awesomeness]

My fan in my Freightliner even on wildfires slow going on hills etc would only come on once in a while on a Cat 3406C loaded to 48,000 lbs GVW. You knew when it came on too it was loud. Seem like if it uses 57 HP which is a lot and hardly comes on less HP and more fan use might be better? I am sure the Military used the worst conditions to figure out the needed fans CFPM of air moved. Having 57 more HP sound pretty good to me?

Yes, absolutely. The difference in military and civilian design is that for the military you must meet their specifications under all (extreme) conditions, and for the civilian market it only needs to be able to do it under ideal laboratory conditions.

These trucks all use the same cooling system (e.g. fan, radiator, etc.), so it was designed to support, with a safety margin, whichever of them is the worst case (e.g. 290HP MTV tractor pulling full load, in 120°F heat with no vehicle speed to create airflow, etc.). So on an unloaded 225HP LMTV, at 90°F, etc., it's going to need considerably less, though I don't know how much less would be reasonable.

 

[JD4044M]

Here is a good read on Clutch Fans, HP used and proper Air pressure and Clutch Friction Surface break in. Clutch Fan Info

 

[Awesomeness]

My mistake, it is a 26kW (35HP) fan. This military study is where I got the number from. It also talks about the airflow requirements, stating that the "current M1078 cooling fan system required air flow of approximately 8000 to 15000 Cubic Feet per Minute (CFM) (226 to 425 m3/minute)".

NOTE: This is also a good read for all the BS'ers that claim they get 10-12MPG. NO WAY IN HELL. These trucks get 5-6MPG average, and maybe an extra 0.5MPG with the 3.07:1 gears and modest drivings speeds. My best tank ever was 8MPG, on a long straight mostly downhill couple hundred miles, on a cool morning in Arizona. My lifetime average is 5.5MPG.

 

[JD4044M]

Heck I only get 10 MPG in my 79 Chevy 4x4 with a Bored out 454 so It won't bug me much the MPG look what you are driving better than a Prius! Anyway just talked to the Transport they are in Kansas and my M1078 will be here Monday Morning Now I am so pumped up it is going to happen!

 

[Awesomeness]

Heck I only get 10 MPG in my 79 Chevy 4x4 with a Bored out 454 so It won't bug me much the MPG look what you are driving better than a Prius! Anyway just talked to the Transport they are in Kansas and will be here on Monday Morning Now I am so pumped up it is going to happen!

I'm just pointing it out, because there are several members, who have been around for a long time, that swear they get 10-12MPG. It gets everyone's hopes up, and then we get a bunch of new people in here with unrealistic expectations. The topic comes up periodically. I recently had a guy tell me that there must be something wrong with my truck if I'm only getting 5-6MPG, because he has owned dozens of these and always gets 10-12MPG in all of them. The problem is that those stupid posts never go away, and people read them and believe it (perhaps wanting to believe the most optimistic info available).

 

[Coffey1]

Well mine gets better than the hemit that I had lol

 

[Ronmar]

FYI:
27.5” fan and a 10.5” hub works out to be 3.52 sq/ft of blade area.

Fan Clutch Engaged:

750 RPM = 2100 FPM Velocity measured X 3.52 SQ/FT = 7392 CFM.

2600 RPM = 7000 FPM measured X 3.52SQ/FT = 24,640 CFM.

There are other ways to do this. Like with a electric controlled clutch used on several large trucks like the Chevy Kodiak with a cat 3116... you just have to remember it has a left hand/counter clockwise rotation as seen from the drivers seat. I believe this is known as a “standard“ rotation. You would of course have to machine a custom adapter to connect to the crankshaft damper...

 

[Ohiobenz]

If anyone needs a good fan and clutch, I have a like new one off my LMTV, and a viscous clutch one of a civilian OTR truck.