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M939 Oil Change, Best Oil, Tips and Tricks

simp5782

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Rule of thumb on any military truck. Never trust your gauges. If you think its suspicious take 5 mins and screw a pressure tester into it and vary them against the readings. You can also solder a ground wire directly to the sending unit and establish a good frame ground. Also try to clean the port on the bottom of the unit. May have gunk. Add stabilent 22 to the connection point.

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99nouns

Member
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Ocala, FL
That is odd. What brand of oil filter are you running?
I replaced it with the original one from ebay had a good deal.
CAM00146.jpg

Rule of thumb on any military truck. Never trust your gauges. If you think its suspicious take 5 mins and screw a pressure tester into it and vary them against the readings. You can also solder a ground wire directly to the sending unit and establish a good frame ground. Also try to clean the port on the bottom of the unit. May have gunk. Add stabilent 22 to the connection point.

Sent from my SM-G860P using Tapatalk
If I only had a pressure tester!!! What does it mean to have a high pressure in acceleration, is it clogged somewhere? I know the gauge was stuttering before but it never went high like that before. Should I look for any symptoms? I need to run down to auto store and see if they have a pressure tester for loaners.
 

simp5782

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I replaced it with the original one from ebay had a good deal.
View attachment 674598



If I only had a pressure tester!!! What does it mean to have a high pressure in acceleration, is it clogged somewhere? I know the gauge was stuttering before but it never went high like that before. Should I look for any symptoms? I need to run down to auto store and see if they have a pressure tester for loaners.
They will loan you one. Gauges are always iffy. Sure way is to swap it all to a manual gauge for about 75$ ;

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M35A2-AZ

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Mechanical gauge fixed the erratic and high oil pressure issue. Everything is normal now.
I had a erratic oil gauge and it trued out to be the wire coming from the sending unit to the gauge. I just replaced that wire and all good now.
 

99nouns

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What mechanical gauge did you go with?
I got this from NAPA

https://www.napaonline.com/en/p/BK_5011731

It came with everything, the ports, adapters, tubing. I couldn't afford $70 original gauge at the moment, if took me 5 mins to install, only issue is no light because of it doesnt have clear housing to work with truck's internal lighting, it does look like a new guy in old school among all the other gauges but it is my project truck so I might think of something else later. It works right now and that's what matters.
 

99nouns

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I had a erratic oil gauge and it trued out to be the wire coming from the sending unit to the gauge. I just replaced that wire and all good now.
I dont know how did you figure to replace the wire, that wire twist around and travels to more places than New York City Subway.
 

simp5782

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I dont know how did you figure to replace the wire, that wire twist around and travels to more places than New York City Subway.
Leave the old wire in its place and simply just run a new one thru the firewall hole up and over the steering column and into the dash

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M35A2-AZ

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99nouns Yes just run a new wire and route it the best way you can. I think there is a pass though on the fire wall close to the black box.
That is were I run into the cab.


I dont know how did you figure to replace the wire, that wire twist around and travels to more places than New York City Subway.
 

Cape Coastie

CWO4 ENG/MSS, USCG, RET.
528
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Sandwich, MA
Yes leaving the bad/defective wire in place and adding the new one is very common in the marine industry. It is called "abandon in place". Usually much quicker than pulling old cable and time is money.
 

simp5782

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Just an update as I have always ran Rotella 1540 just basic stuff. I ran the T6 synthetic for a bit and my engine didn't like it. She got loud. No surprise.

I just did a recent oil change and went over to Delo 400 SDE cause it was on sale for $10 a Costco. I know this stuff is fairly new only being out about a yeaer. Some say not for older engines, some say it is fine. I am going to do a 3000mi oil analysis and go from there, I also have a bypass filter that adds additives back into the system but I guess ill have to check that opinion out later with my own lab results. I was running standard rotella 15 to 18k with the bypass unit. I wasn't testing it though.
 

rickyrecon

New member
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Forest/VA
I just first time going to change my oil on my M927-A2 and I know, A-1 and A-2 are little different in procedures, but I really wanted to put up decent newbie reference and question platform for all the opinions and options so where other people can ask their questions under one thread.

I have changed oil before, never diesel, my general procedure as follows.

1-Add motor flush run engine for 5 mins.
2-Open drain plugs, let it drip long time.
3-Remove filters, clean housings.
4-Fill new filter with oil apply oil to gaskets and install, dont over tighten.
5-Put on oil plugs back on and fill with oil.
6-Run engine 5 mins, shut engine 10 mins check oil again.
7-Check oil again next day, add as necessary.

Please feel free to point out any mistakes above but my main question is what oil should I use.

So manual TM 9-2320-272-10 pdf page 67 or paper page 0002-15 says

View attachment 671875

So I take that as 15-40 oil for engine,
but what brand without holing the pocket and what does OE/HDO stands for?

I saw in the wally world all,
Castrol 15-40 5qt 12.xx
Mobil 15-40 5qt 25.xx
chain part stores were about 10 bucks more

I know Cummins prefers Valvoline as their official oil, and I am confused about the price difference, why so large? What do you use? Any suggestions?

Thanks in advance for the replies...
I know this is an older post - but I am having a terrible time keeping my oil filter assembly from leaking. Any advice is appreciated. I have an M939 and just replaced the canister filter and gasket. I feel dumb - that I can't figure this out. I put the gasket around the head assembly then tighten the canister 'pretty tight' yet I still get a small stream. ... maybe I'm over tightening and causing the gasket to spill out? It seems a larger gasket would cause a better fit. Any advice is appreciated. Thank you, Rich
 

99nouns

Member
816
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18
Location
Ocala, FL
I know this is an older post - but I am having a terrible time keeping my oil filter assembly from leaking. Any advice is appreciated. I have an M939 and just replaced the canister filter and gasket. I feel dumb - that I can't figure this out. I put the gasket around the head assembly then tighten the canister 'pretty tight' yet I still get a small stream. ... maybe I'm over tightening and causing the gasket to spill out? It seems a larger gasket would cause a better fit. Any advice is appreciated. Thank you, Rich
I hope Wes is around to say something!
 

98G

Former SSG
Steel Soldiers Supporter
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AZ/KS/MO/OK/NM/NE, varies by the day...
I know this is an older post - but I am having a terrible time keeping my oil filter assembly from leaking. Any advice is appreciated. I have an M939 and just replaced the canister filter and gasket. I feel dumb - that I can't figure this out. I put the gasket around the head assembly then tighten the canister 'pretty tight' yet I still get a small stream. ... maybe I'm over tightening and causing the gasket to spill out? It seems a larger gasket would cause a better fit. Any advice is appreciated. Thank you, Rich
Convert to spin on and call it done. I think floridianson had a spin on conversion for sale reasonably.
 

juanprado

Well-known member
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Metairie/La (N'awlins)
I 2nd that. Fleetguard sells the conversion plate. Change to a modern spin on filter and there are many choices for filter such as extended capacity and life etc.
Canister technology is way old school and much better choices now.

Not that expensive. Use a baldwin or fleetguard. Baldwin OB-1368
I recall others having issue with wix/napa.
 
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