LMTV fan runs frequently

[sargentwolf]

So my LMTV has an annoying issue Ive discovered.

The fan runs VERY often. On the road at speed, usually every other minute for 30 seconds then shuts off. Vehicle is unloaded, I dont have a tarp installed, not towing a trailer. Im usually running at around 50 on the highway, not flat out and over STL highways, so mostly flat roadways.

Temp gauge says its at 215-220°F when fan starts, runs, drops to 200°F, shuts down, repeat. yes, STL is going through a massive heat wave, but has been going on at night, ambient air usually around 85°F. I dont like to run or work on the truck in the heat, wayyyyy too hot right nowadays.

Should I start by changing the belts, do a radiator flush/fill, or what? Its not overheated YET, but want to nip this in the bud.

 

[tennmogger]

Sounds normal to me. I'm on an extended drive and for several days at 90+ temp, westbound so the sun is on the front, pushing 50 mph, the fan cycles just like yours. However our gauges read a little differently. My temp gauge shows 200 when the fan kicks in and it drops somewhat below that to turn off. I believe it's working just as it is supposed to.

We must remember that this truck runs most of the time with the fan only driven through a viscous coupler. Most likely at road speed the fan is driven mostly by air ram effect from air passing through and adds little to the cooling, maybe even restricting air flow somewhat. Only when the fan clutch locks does cooling really start. I think it's remarkable the system works as well as it does without a powered fan most of the time.

Do you ever see the engine temp warning light? Probably not, because the fan is doing it's job.

I do not like the short cycling either. Sometimes it would be nice to have a 'fan on' switch to force the fan 'on' all the time. Switching the fan on would save clutch wear.

Maybe a cooler thermostat would give the system a little more head room. I believe my thermostat is 190 or higher.

 

[mkcoen]

Working exactly like it should so nothing to do to alter that. Still you SHOULD change all your belts if they show any wear. I put off changing the belts on my Gama Goat and when they went they fried the motor when it overheated.

The alt belts are extremely simple to change but the water pump belt will take a while so start early in the morning when you'll have a couple of cool hours.

 

[Suprman]

It does sound correct for highway use. That engine makes alot of heat at 57mph you are around 2500rpms. I would still flush the coolant and I have found trucks with partially clogged radiators just from dirt and debris picked up over time. If you can get in there you can spray a hose thru the back and get the junk out the front of the radiator.

 

[Oxyacetylene]

I am going to diverge just a little and say maybe your cooling system is not working at full/peak efficiency. I drove mine yesterday evening, when the temps were probably about the same range, 85 or so degrees. Full out running down the highway my temp stayed right around 200 according to the gauge. The fan didn't kick in until I slowed down to make some turns, at which point the temp rose some. Now granted it was a short highway run of only maybe 10 miles each way, but the truck was up to temp by the time I got onto the highway. In general the fan on mine doesn't cycle on very often unless the outside temps are 90+ and I'm running it wide open, or lots of stop 'n go, etc.

Maybe yours is working perfect, but if you are concerned then I would check and maybe flush the radiator, make sure you are getting good coolant flow.

 

[sargentwolf]

Took a run this morning before it got stupid hot, even at lower speeds (35-40) runs every minute. I'm going to try washing the radiator as well as taking it to jiffy lube for a coolant flush.

Now, what I remember from when I was in the army, the LMTV fan only really ran like this when we were towing either the double generator trailer or the big expandable shelter behind it at high speed. Rest of the time, it didn't really run much. This was in Arizona too, that's why I was concerned.

 

[TNriverjet]

I'd love to see the Jiffy Lube technician's face when you pull in the M1078 and hand him a coupon for a $29.99 coolant system flush!

 

[aleigh]

I do not like the short cycling either. Sometimes it would be nice to have a 'fan on' switch to force the fan 'on' all the time. Switching the fan on would save clutch wear.

Mine is broken and stuck on. Problem solved...

 

[Overdrive]

sargentwolf,
I am outside STL near Wentzville. Since the heatwave is still going on I will take mine out for a spin on I-70 this weekend and see how the fan behaves. When I pulled a 1082 home from Ft. Leonard wood, with outside temps around 68 if I remember correctly, my fan only came on once but I haven't been out on a highway drive in this crazy heat we are having. Will see how she does since I recently flushed the radiator and put in ELC coolant then will report back.

FYI: When I changed out the coolant I replaced the thermostat. I used the part number in the -24P (CAT 119-3075) which is a CAT part. Rated at 82C/179.6F. Both the thermostat I pulled from the truck and the new part are 180 degrees.

OD

 

[Pointman0853]

As we are seeing triple digits here in Northwestern Nevada, I recently rebuilt my fan clutch and did a complete flush. The coolant coning out looked like pure Glycol. I filtered it using a paint strainer and reinstalled it. The three new belts were also replaced. Cannot stress enough to have a look at those. Mine looked good until I removed them and they all were cracked and dried out. Not something you want to do while traveling.
I also discovered a ripped intercooler boot that was causing boost pressure loss that got changed out as well. Once you begin peeling back the onion there are always other items you will find if you keep your eyes open.
Everything is buttoned up and I'm on the the next project. With the heat, my fan only comes on when heading up a grade. Otherwise she's quiet..

Pointman
Pointman

 

[DiverDarrell]

True words about the onion. Doing my alternator I found the fuel lines look weak. Fixing the air dryer, I found the ctis to leak. Tightening the throttle cable I found a worn intercooler boot. And the list goes on and on...

 

[Pointman0853]

The Gov isn't selling these because they are in great shape.

We should form a small African Republic, then they will send equipment and mechanics to keep it all going, eh?

Pointman

 

[dsanderlmtv]

I have a question, should the fan spin freely when the motor is off? I try to move the fan by hand and it is VERY stiff, but I do notice that it turns on when it starts to get over 200 degrees but only for a few seconds then goes off again.

 

[Pointman0853]

This is normal.

When the truck is cold and the air pressure has bled down, you should NOT be able to move the fan by hand. When the engine first starts, the fax will be engaged until the air pressure reaches a point when the fan will disengage and freewheel on the bearing in the fan clutch. When the engine reaches 200+/- degrees, the temp sensor triggers the valve under the passenger kick panel in the cab to release the fan clutch air supply, then the fan will be heard to operate. What you describe sounds normal, however... You should not be able to move the fan when the truck is cold. You may have a friction ring about to reach its operational limits. The rebuild kit is available from Borg-Warner and runs around $85.00. That is providing the bearings are usable..

I just went through a fan clutch rebuild. PM me if you need personal help..

Pointman

 

[dsanderlmtv]

This is normal.

When the truck is cold and the air pressure has bled down, you should NOT be able to move the fan by hand. When the engine first starts, the fax will be engaged until the air pressure reaches a point when the fan will disengage and freewheel on the bearing in the fan clutch. When the engine reaches 200+/- degrees, the temp sensor triggers the valve under the passenger kick panel in the cab to release the fan clutch air supply, then the fan will be heard to operate. What you describe sounds normal, however... You should not be able to move the fan when the truck is cold. You may have a friction ring about to reach its operational limits. The rebuild kit is available from Borg-Warner and runs around $85.00. That is providing the bearings are usable..


I just went through a fan clutch rebuild. PM me if you need personal help..

Pointman

Thanks Pointman, now that you described it I think mine is running fine but if not I will contact you.

 

[reelclassic]

I have a 3126 Caterpillar and my fan runs all the time even when sitting at idle. Any ideas?

 

[reelclassic]

Coolant temp never seems to get above 165 - 170. is this about where a 3126 should stay.

 

[Suprman]

It stays low because your fan runs all the time. Air keeps the fan off. So you could have no air to the fan clutch. Or it could just be stuck from sitting before you got it. With the truck off and the air drained, take the air line off the fan clutch and hook an air compressor to it. You need around 70psi to release the fan clutch. See if it releases and freewheels. If not give the fan clutch a whack with a big wrench.

 

[reelclassic]

Thank you very much for your help. Have a good day.

 

[Pointman0853]

I have a 3126 Caterpillar and my fan runs all the time even when sitting at idle. Any ideas?

Reelclassic,

The fan will be engaged at startup. Once air pressure has built up, it should disengage. If not, you are not getting air to the fan clutch. Start by checking for air supply in the line that runs to the top of the fan shroud. Do this after pressure has built up and with the engine off. If no air escapes, check the small air valve under the passenger footplate..

Pointman