Oil pressure averages

[BluePrintArmsCo]

Working on a 1990 M923A2 5 Ton 8.3. Getting acquainted with it and wondering about oil pressure averages.... I'd add pictures but unsure how to using my phone.

Upon startup (below 120 degree engine temp) I was at roughly 40lbs oil pressure.

After nearly a 25-30min idle warm-up I noticed I was somewhere around 25lbs of oil pressure at 140 degrees at idle. Once it warmed up to the point that the temp needle came up I gave it about 10% throttle and the pressure came back up to 40lbs range.

Are we within average ranges or should we be concerned? Didn't have any abnormal smoking...it was driven from Gov Liq site in Columbus Ohio to Mt Vernon Ohio without issue and had appropriate fluid levels.

Based on dates written on oil filter it hasn't seen a service since July of 2012... aside from completing a standard LOF service should we be concerned about those Oil Pressures?

I suspect we're in ok ranges but wanted to be sure before I direct my attention to the leaking CTIS after the LOF.

Thanks!

 

[simp5782]

Hook a manual gauge up to the engine and check oil pressure that way. You are new to the forum so I assume to the MV world all together. Never trust your gauges. Its a rule of thumb. They can vary widely on their readings.

https://www.steelsoldiers.com/archive/index.php/t-143799.html

https://www.steelsoldiers.com/showthread.php?125711-M923A2-oil-pressure

.

 

[74M35A2]

Your pressures are fine. 8.3L oil pressure is nearly identical to a 350 Chevy. 10psi per 1000rpm is plenty. The stock MV electric oil pressure gauge is terrible in accuracy, resolution, and reliability. It really just confirms it is not zero. But at least for an 8.3L, if it has oil, it will have oil pressure. I don’t think there is even a single case here of an oil pressure problem on an 8.3L. One guy is even running a cracked block.

 

[m715mike]

I know this is an old thread... I've read a few of them. It seems that low oil pressure is common on the 8.3L. I have the opposite problem.

I fired-up the M936A2 yesterday. It idled for a few minutes with the gauge showing 60 psi of oil pressure at cold idle. After a few minutes of idling, I increased the RPMs to 1000 - 1500. At this point the oil pressure gauge started bouncing between 60 psi and 120 psi. Then the gauge pegged all the way to the right (pictured below). I shut the truck down and the oil pressure gauge stayed pegged to the right (i.e., did not return to zero).

After letting the truck sit for 10 minutes-ish, I fired it back up. The gauge went back to bouncing between 60 psi and 120 psi. I let it idle for a minute or two and then shut the truck down again. This time the gauge returned to zero.

The truck ran fine and sounded great. There is plenty of oil in the truck, maybe too much. The dip stick shows just over the full mark. It's been at least six years since the last oil change (maybe longer). This truck is new to me, and changing the oil is next on my list of to-do's.

Questions:

1) Out of curiosity, what causes high oil pressure in an engine?

2) What is the likely issue and where should I start looking with my M936A2: something wrong in the engine, bad sending unit, bad gauge, bad ground on the gauge, etc?

2) Seems like checking the oil pressure with a mechanical gauge is a good idea, but I've never done that before. What do I need to buy, and where does it connect/plumb into the engine?

3) What else should I be thinking about?

 

[74M35A2]

Cummins oil systems are about as simple and reliable as a small block Chevy. Yet the gauges and senders are about as cheap as Chinese tin foil. I switched mine to a matching full sweep mechanical gauge, and then observed readings much more inline with what one would expect.

 

[simp5782]

Switch to mechanical. Cheap enough and accurate

You can get mechanical water temp. Oil temp. Oil pressure matching set for under $150 in DDC vdo gauges

Use standard hydraulic fittings and push lock hose

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[charlesmann]

I know this is an old thread... I've read a few of them. It seems that low oil pressure is common on the 8.3L. I have the opposite problem.

I fired-up the M936A2 yesterday. It idled for a few minutes with the gauge showing 60 psi of oil pressure at cold idle. After a few minutes of idling, I increased the RPMs to 1000 - 1500. At this point the oil pressure gauge started bouncing between 60 psi and 120 psi. Then the gauge pegged all the way to the right (pictured below). I shut the truck down and the oil pressure gauge stayed pegged to the right (i.e., did not return to zero).

After letting the truck sit for 10 minutes-ish, I fired it back up. The gauge went back to bouncing between 60 psi and 120 psi. I let it idle for a minute or two and then shut the truck down again. This time the gauge returned to zero.

The truck ran fine and sounded great. There is plenty of oil in the truck, maybe too much. The dip stick shows just over the full mark. It's been at least six years since the last oil change (maybe longer). This truck is new to me, and changing the oil is next on my list of to-do's.

Questions:

1) Out of curiosity, what causes high oil pressure in an engine?

2) What is the likely issue and where should I start looking with my M936A2: something wrong in the engine, bad sending unit, bad gauge, bad ground on the gauge, etc?

2) Seems like checking the oil pressure with a mechanical gauge is a good idea, but I've never done that before. What do I need to buy, and where does it connect/plumb into the engine?

3) What else should I be thinking about?

View attachment 825836

So, i had the opposite, went from 20ish psi, to nothing. I too shut it down, checked oil level and level was fine. I went to advance (first parts house i came to, since it was getting dark and wanted to get it checked before it got dark. I removed the sending unit (driver side, aft of the manual primer pump with a single wire coming from the unit) took it with me to confirm i got the correct adapters with the mechanical gauge, hooked it up and started the truck. I was getting close to 60psi initially, but didn't let it run enough to see if i got a drop in psi. See my thread here https://www.steelsoldiers.com/threads/low-no-oil-pressure.201103/ with info on alt psi gauges.

 

[74M35A2]

The one I went with matches, including the back lighting. I think it was listed as fitting a Willy’s.

 

[m715mike]

The one I went with matches, including the back lighting. I think it was listed as fitting a Willy’s. View attachment 825863

Clint, I read your install thread on that. I like how it came out!

 

[74M35A2]

Me too. I should have painted it’s bezel ring to match but was lazy. She works good though. Like the full sweep, mechanical, and matched lighting. Thanks bro.