D25U2620 low oil pressure

My oil pressure started showing zero the other day so I shut it down and restarted it a few days later and seen the gauge spike then drop to zero again. I put a different gauge on to actually see the pressure. It starts at 25 and as heats up starts falling. I’ve seen the attachment that has been posted several times about the low oil pressure these run. As low as 4 psi!? Reading the book it sounds like the pressure regulator starts working at 30psi and the pressure relief opens at 90psi. Therefore I’d say the pressure should be between the two at all times. Can someone clear this up for me. My old gauge was acting real sticky when testing it with air so I assume it has gone bad. Thank you. Kyle.

If you have enough oil, how about a sludged pickup screen, or stuck relief valve? Or even a pickup that is loose on the pump?

4 psi at what rpm? At idle that would be ok but I would think it was marginal at higher rpm.

Those engines have an inlet regulator built into the pump that controls pump output in response to pressure at the center main bearing. It sounds as though yours is working if it starts out at 25 psi cold so I would be looking more at bearing clearances, pump wear and oil viscosity than the pressure regulating valve. I suppose if the pressure drops immediately after it builds up, it could be a broken or weak spring in the inlet regulating valve. As soon as pressure builds up it would push the valve closed, starving the pump for oil and dropping the output pressure. A gradual drop as the oil warms up sounds more like excessive clearance somewhere or very low oil viscosity.

Just a point of interest, I got a 212 grader with no oil pressure. Pulled the engine and took the pan off to investigate. I quickly realized that someone had been in the engine before because of their extensive use of red silicone. In the end I discovered the pump had ingested one or more roll pins that had been left inside the suction bell. There were still a couple left in there when I took it apart! Not having a new oil pump, I cleaned up the gears and the housing, reassembled it (without stray hardware) and got good oil pressure according to the CAT gauge. The pressure control valve plunger and spring was fine.

Just as an update I had dropped the oil. Looked good no metal and replaced it with new 30w and new filter which was hard to find. This was the other day and the pressure readings were the same as I said earlier FYI had a hard time finding a filter to fit it. The number out of the book crosses to a filter with too small of a inside measurement so I’m using a Napa 1161 or cat 1r0659. Napa 1165 and cat 1r0729 do not fit.

The NAPA 1161 is a full flow filter. The tractor came with the bypass filter arrangement but CAT offered a field conversion kit when the full flow design was introduced and many older machines were converted.