When I start my 96 5.9 3500, seems like the oil pressure barely gets to 40. Then when I drive it seems to hover between the plain white line on the left. Don't know what that number is..... it doesn't say.

I just changed my oil and the old oil filter wasn't filled to the brim.
i
It was about 75 or 80% filled.
Is this normal? Or is my oil pump going??
If it is... are they expensive and a how hard is the labor ?
Thanks for the info.

Your oil pressure is fine. Factory sending units are inaccurate garbage, and poorly located. Stick a mechanical gauge in the extra port on your oil filter housing to verify your pressure is correct.

Minimum spec per Quickserve is 10 psi at idle (most original engines at this point will be about 30) and 30 psi at rated speed (rated speed is on your engine dataplate, most original engines at this point will be around 60-70).

It is normal for oil filters to drain back (siphon) when the engine is shut off. Your oil pump isn't "going". I suggest you open the factory service manual to learn how it works and what it looks like. My oil pump is the same one that it has had since the truck was new.

I'd be a very rich man if I received a dollar every time Gary told someone to use the search feature of this site or read the FSM.
Why don't you just use cut and paste and save your effort?

I installed a pressure gauge just as Dauntless suggested and put it on the steering column.

The new oil pump for our 12v's is now the same as the 24v oil pump and flows more. I can't remember the percentage.

PDD is coming out with a huge upgrade for the 12v pump and I think it's from the 8.3 but will require replacing the pick up tube as well. I'm looking forward to that.

Changing the oil pump by itself is easy but getting behind the gear cover requires removing at least the full fan assembly, shroud, harmonic balancer, and a few other little bits. You'll need a new crank seal as well. However, it's doubtful you need an oil pump.

The "old" 12v pump and the 4939587 (24v pump) have the same displacement. There are minor changes to the rotor tip geometry which may help the newer pump's volumetric efficiency, but that potential few percent and then the difference between a used pump and a new pump is all the flow gain there is. The outer rotors interchange between the old and new pumps, turn over freely, and would operate normally in a running engine.

The original oil pump in my '94-manufactured engine was a 3926203. This part number superseded SIX others. The '6203, and the 3924720 (the part number just before the '6203) both have the same displacement as the '9587. Based on how the pump installs into it's bore in the block, I'm highly skeptical that any of these 5 earlier part numbers could have been a smaller displacement unless they made a radical change to the design of the pump.

I think "the 24v pump flows more" is just another baseless internet myth.

That just may be the case. It's unfortunate so many diesel performance companies are printing unverified myths though. It's hard to tell these days I guess. All these companies say differently. Maybe just parroting a myth. Maybe not.

Pure Diesel Power
https://puredieselpower.com/dodge-pr...l#/product/812


CPP
https://cppdiesel.com/cummins-4939587-oil-pump-89-02/


KLM Performance
https://www.klmperformance.com/produ...21998789525588

Yeah, it's everywhere, and I don't expect that misunderstanding will ever self-correct. It's unfortunately in the same category as 'cold-air intakes and 4" exhaust are power-adders.'

I took it for granted myself until I took several apart and started playing with them.