FMTV 3126 Engine options

[MatthewWBailey]

Hey my 6pz is the same year as yours just a couple thousand off.View attachment 925063

Is yours giving any issues?

 

[Skyhawk13205]

Is yours giving any issues?

Not yet, oil PX is about 60 at cruise and 30 at idle when up to temp. I run 15w-40

 

[MatthewWBailey]

They like to crack on the drivers side at the rear - behind the starter. Plenty of non-military applications that experienced that failure and in our application the operating conditions can be significantly more harsh. Slowing down the drivelines with the ECO hubs helps for sure.

If I was replacing a 3126 though I would just go straight to the C7.

I drove it today with the 'new' MVT tires. Each has 22-23/32 tread depth. Felt really smooth, no buzz saw sound, no bouncing. Of course I had gotten used to the xml's so it was a noticeable deletion of sound. felt like a typical all terrain tire.

When I drop the pan to do the oil pump, I'll send the ecm. Pulling the cooler too once it's offline. Not sure how long I got with this block but I'll keep pouring oil in it. The Cat 3304 from '86 and 3054T from '06 I have consume almost no oil over a 500hr time. One has 3200hrs, the other 5900hrs. Granted they're different engines but this 3126 seems to have issues internally.

 

[MatthewWBailey]

Not yet, oil PX is about 60 at cruise and 30 at idle when up to temp. I run 15w-40

Yeah my guage is zero at idle at full temp. I keep it at 800+ rpm if stopped at lights. I'm using Amsoil 15w-40 synthetic

 

[GeneralDisorder]

Yeah my guage is zero at idle at full temp. I keep it at 800+ rpm if stopped at lights. I'm using Amsoil 15w-40 synthetic

@Lostchain had the exact same situation with 6,500 miles on his 3126. Changed out his pump and all was fixed. His thermostats were also bad and causing overheating.

 

[Skyhawk13205]

Yeah my guage is zero at idle at full temp. I keep it at 800+ rpm if stopped at lights. I'm using Amsoil 15w-40 synthetic

Based on your diagnostics you prob think it may be the last 5 bullet points?

 

[MatthewWBailey]

Based on your diagnostics you prob think it may be the last 5 bullet points?View attachment 925068

Ill have to drop the pan and look in there. Since the pump is a known flaw I can start with that for sure and verify #5 above. (I rebuilt a ford 302 years ago and forgot a plug and saw what #4 acts like). I can pull bearings to check them but I don't know what to check for thickness without a Cat service manual on this engine. I saw that @ckouba just replaced all his at the same time. that seems like a no brainer.

 

[GeneralDisorder]

Ill have to drop the pan and look in there. Since the pump is a known flaw I can start with that for sure and verify #5 above. (I rebuilt a ford 302 years ago and forgot a plug and saw what #4 acts like). I can pull bearings to check them but I don't know what to check for thickness without a Cat service manual on this engine. I saw that @ckouba just replaced all his at the same time. that seems like a no brainer.

Yeah after @Lostchain 's experience and when @ckouba 's HEUI pump left the chat we included the main oil pump and checking the oil cooler for flatness to the list of preventative items while it was blown apart. Fortunately his HEUI pump did not disintegrate catastrophically into the injectors so those didn't require replacement.

 

[Skyhawk13205]

Ill have to drop the pan and look in there. Since the pump is a known flaw I can start with that for sure and verify #5 above. (I rebuilt a ford 302 years ago and forgot a plug and saw what #4 acts like). I can pull bearings to check them but I don't know what to check for thickness without a Cat service manual on this engine. I saw that @ckouba just replaced all his at the same time. that seems like a no brainer.

If you need any tech data I use TM 9-2320-312-24-2, it has been a good reference. I used it for my overhead valve adjustment and wiring in my cruise control, and diagnosing my fuel feed issue.

 

[hike]

If you need any tech data I use TM 9-2320-312-24-2, it has been a good reference. I used it for my overhead valve adjustment and wiring in my cruise control, and diagnosing my fuel feed issue.

TM 9-2320-312-24-2 is where? That doesn't appear to be a link—

 

[sue]

A lot of civilians with the small cats have just put in a older all mechanical
Rebuilt cummins. With the price of cat parts lately might be worth it?

 

[Skyhawk13205]

TM 9-2320-312-24-2 is where? That doesn't appear to be a link—

Give it a search on Google, it is a TM for a yard tractor that has a 3126

 

[coachgeo]

Yeah my guage is zero at idle at full temp. I keep it at 800+ rpm if stopped at lights. I'm using Amsoil 15w-40 synthetic

Adept Ape (a CAT mechanic Youtuber) just had similar.... on a rebuilt engine. Long story short he dropped oil pan and low and behold the oil pick up tube was not tight to the base of where it attaches (to pump I assume)... allowed air in, would aerate oil etc. . Buttoned it up and all good.

 

[MatthewWBailey]

Adept Ape (a CAT mechanic Youtuber) just had similar.... on a rebuilt engine. Long story short he dropped oil pan and low and behold the oil pick up tube was not tight to the base of where it attaches (to pump I assume)... allowed air in, would aerate oil etc. . Buttoned it up and all good.

Interesting. That should be revealed quickly once I get in there.

update: today I finally got the oil pan off. The pick up tube is secured to the pump. Screen was clear. I drained the oil into a new bucket with a large magnet in the bottom. I'll pull the magnet tomorrow to see what metal dregs get caught. It's like inorganic fishing.

 

[MatthewWBailey]

TM 9-2320-312-24-2 is where? That doesn't appear to be a link—

I found it here. ....
www.liberatedmanuals.com/TM-9-2320-312-24-2.pdf

 

[MatthewWBailey]

Anyone know what plug size this is? Idk how long it's been missing but it's a threaded hole..

 

[GeneralDisorder]

Looks like a pipe plug. Here's mine. I'm guessing that is the access hole for the flexplate to torque converter bolts.

 

[MatthewWBailey]

Looks like a pipe plug. Here's mine. I'm guessing that is the access hole for the flexplate to torque converter bolts.

View attachment 927154

I tried a 1-1/2 but way to big. Maybe 1-1/4" unless it's another metric curve ball. Maybe it's in the parts TM

 

[Ronmar]

Yea I think it is standard national pipe. Yes, flex plate bolt access…

 

[MatthewWBailey]

It's 7X7730 in the TM but I'm going to try the hardware store first. Glad I snooped around in there as I was removing the exhaust. Found this and 2 loose trans mount bolts, and both my rear driveshaft u joints are loose.