Did some work on Mack motor requiring removal of oil filter housing so fitted new filters. On startup oil pressure stayed at 30psi regardless of revs where normally 60psi at idle and 75psi with a few revs (cold). Took off Donaldson and replaced with same. Long story short as a last resort fitted new filters and all back to normal. Can anyone explain?
I haven't worked on that part for years but I sort of remember two things which dropped the oil pressure. The first one was a blocked oil filter or the wrong filter which limited the flow and bypassed in the valve over the filters. The other thing was the valve which limits the oil to the piston coolers when it's idling. If it was to stick open, the oil pressure may be affected. Just a couple of suggestions. Kav.