NHC 250 Oil Pressure drops out

[KaiserM109]

With the oil on the dipstick a little below the HIGH mark, when I start the engine the oil pressure starts out at 90 and stays there until I start driving. It begins dropping until after an hour it is right at the edge of the '0'. I put 2 quarts in so that it is 1/8" over full and it stabilizes halfway between the '0' and '30'.

Has anyone had a similar experience? What about adding an oil cooler?

Where is/are the oil filter(s)?

Arlyn​

 

[RustyM923]

I'd start by checking the gauge.

 

[porkysplace]

With the oil on the dipstick a little below the HIGH mark, when I start the engine the oil pressure starts out at 90 and stays there until I start driving. It begins dropping until after an hour it is right at the edge of the '0'. I put 2 quarts in so that it is 1/8" over full and it stabilizes halfway between the '0' and '30'.

Has anyone had a similar experience? What about adding an oil cooler?

Where is/are the oil filter(s)?

Arlyn​

It would probably be a good idea to look at the TM's

 

[jw4x4]

It already has one oil cooler. I don't see how another one would help. Rusty's idea of checking the gauge is a great place to start.

 

[Scar59]

You probably need to add the oil filter adapter and spin on filter. Adding oil to a full system will not increase oil pressure.
Most likely pressure indication issues.

 

[wrenchturner6238]

How long have you had this unit? I am wandering if this is a new problem or it truck new to you?
It sounds like to me if you do not have a gauge, sending unit, wiring problem worn cam bearings can do this type of thing but normally the start up PSI will be lower as well. Does your oil smell like diesel? having fuel in the oil can do this as well. The first thing I would do is install a good manual gauge and go for a test drive and see if it is the same.

 

[M35A2-AZ]

I would put on a mechanical gauge and test it that way.

 

[Carlo]

It seems the gauges the military uses are some of the worst in the world. I agree on check the gauge first. I did have a truck once show max 30 and cleaned the sending unit. The problem disappeared. I sprayed degreaser inside it and let it dry. I did not expect it would work but after I had 90 at cold and 30 to 35 at idle.

 

[Jeepsinker]

Where is/are the oil filter(s)? Arlyn
[/QUOTE]

Dude.... Seriously? Tell me you just got this thing.

 

[WillWagner]

Another thing it could be is the stick marked wrong/wrong one installed and actually not having enough oil in the pan.

IIRC, 5 1/5 low, 7 high, on the stick...in gallons, not quarts.

 

[KaiserM109]

Another thing it could be is the stick marked wrong/wrong one installed and actually not having enough oil in the pan.

IIRC, 5 1/5 low, 7 high, on the stick...in gallons, not quarts.

One quart brought it right to the line, but didn't help the symptom. Another quart took it 1/16 inch over the line and seemed to help.

I once had a Dodge Slant Six that if I filled it to the mark it would burn it down 1/8 inch in a few miles, then run fine. On oil changes the correct amount of oil brought it to the down 1/8 inch mark. Obviously the stick was marked wrong and understandably so because it was a Dodge about the time Chrysler started having quality problems.

I’m not sure how bad overfilling a diesel is, but when it’s back on the road again (dead transmission), I am going to add another quart to see what happens. However, I don’t expect to be doing a road trip with it soon. I may be scrapping the beast.

 

[wrenchturner6238]

Just like any engine if it is to far overfull the crankshaft whips the oil into a good lather and you get air through the oil system (not good) but if you are doing it only a quart at a time unless you put in a bunch of quarts in you are not to bad off. If you add a quart and it makes a difference on oil PSI then you really have a problem and you need to drain it out and measure the oil back in like post #10 said.

 

[bigboy44]

I had a simular problem with a 250 and I unsrewed the sending unit from the block and screwed in a mechanical gauge in place of the sending unit and the oil pressure was good. I left the inner rubber splash guard off so I could see it without lifting the hood. I replaced the gauge with a mechanical one after I found the problem. A spin on oil filter is also a great idea, I put it on mine also.

 

[Csm Davis]

Okay are you working on 809 or 939? The older trucks generally ran lower but also used a mechanical gage. Also what rpm are you talking about idle or 2100?

 

[KaiserM109]

Okay are you working on 809 or 939? The older trucks generally ran lower but also used a mechanical gage. Also what rpm are you talking about idle or 2100?

It is an '84 M923A1 with a Cummins NHC-250 w/14,000 miles. The RPMs when I am worried are 2000 to 2200. I think bigboy44 and wrenchturner6238 have it right.

 

[Csm Davis]

The senders on these trucks tend to be Soso in the reliability dept. I would start there but not sure you will find much sounds like a (loose) engine to me, I would try the mechanical gage and see if you have 20-25psi on hot engine minimum at full throttle any less and I think I would be looking for new bearings. Ymmv