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+--- Thread: CM871 OIL PRESSURE (/showthread.php?tid=10759)
CM871 OIL PRESSURE - untouchable - 09-22-2026
WE ARE HAVING AN ISSUE WITH A CM871 OIL PRESSURE. AT IDLE IT IS SITTING AT 20 PSI, VERIFYED WITH MANUAL GAUGE. WE TORE AND INSPECTED ABSOLUTILY EVERYTING, NEW HEAD, BOTH CAMS, OIL PUMP. RODS AND MAINS, OIL PRESSURE SENSOR, FRONT STRUCTURE RESEALED, OIL COOLER RESEALED. STARTED AND RAN AT 45 PSI. TEST DROVE AND COOLANT TEMP WAS AT 195 OIL PRESSURE WAS 18-20.THE TRUCK HAS ALWAYS RAN 30 TO 40 PSI THEN A SUDDEN DROP AND NOW CAN NOT GET IT TO STAY WITH IN THAT RANGE. ANY HELP WOULD BE GREAT
RE: CM871 OIL PRESSURE - tree98 - 09-22-2026
Your trying to get 30-40 psi of oil pressure at idle?? Your post isn't very clear.
Many many times these low oil pressure problems turn out to be the aftermarket cylinder head. Did you put all genuine cummins parts on it or aftermarket of some kind?
RE: CM871 OIL PRESSURE - mikkhh - 09-22-2026
New aftermarket oil cooler and oil pump?
Aftermarket bearings? Did you check the bearing clearance before installing?
RE: CM871 OIL PRESSURE - Rawze - 09-23-2026
(09-22-2026 )untouchable Wrote: WE ARE HAVING AN ISSUE WITH A CM871 OIL PRESSURE. AT IDLE IT IS SITTING AT 20 PSI, VERIFYED WITH MANUAL GAUGE. WE TORE AND INSPECTED ABSOLUTILY EVERYTING, NEW HEAD, BOTH CAMS, OIL PUMP. RODS AND MAINS, OIL PRESSURE SENSOR, FRONT STRUCTURE RESEALED, OIL COOLER RESEALED. STARTED AND RAN AT 45 PSI. TEST DROVE AND COOLANT TEMP WAS AT 195 OIL PRESSURE WAS 18-20.THE TRUCK HAS ALWAYS RAN 30 TO 40 PSI THEN A SUDDEN DROP AND NOW CAN NOT GET IT TO STAY WITH IN THAT RANGE. ANY HELP WOULD BE GREAT
maybe some more details?>.. when did it start?. etc?.
.. and/or does oil pressure come back for a while and then fall off again after a filter + oil change?.
.. and like others said.. did this happen after a rebuild?... or shortly after?. ... and does the engine have all oem or some after-market parts?.
RE: CM871 OIL PRESSURE - untouchable - 09-23-2026
The unit has always had 40 psi of oil pressure at start up cold and would stay around 30 at operating temp also. the customer started it and found it sitting at 30 psi at start up then dropped to 15-20 after warm. the last rebuild was 200k miles ago, we found cam bearing wear, cam wear on the valve cam, rods and mains worn. all parts are aftermarket execpt for the oil pump. the oil pressure has not changed after we replaced the worn componets. we are at a loss of what could be the next step on correcting the issue. we understand that the oil pressure is in spec for cummins but the customer will not accept the oil pressure being under 20.
RE: CM871 OIL PRESSURE - marek4792 - 09-23-2026
How is the geartrain bearings and shafts? Every now and then on the socials you'll get a post where the gear bearing spun and trashed everything.. Worth a look..
RE: CM871 OIL PRESSURE - untouchable - 09-23-2026
All the bearings and gears look good in the gear case, we resealed the gear case as well to verify the gear case seal did not blow.
RE: CM871 OIL PRESSURE - tree98 - 09-23-2026
You still aren't clear on when this happened. You said "the customer started it and found it at 30" ..... so one day out of the blue they started it and it was at 30 psi ?? You seem to be leaving information out.
RE: CM871 OIL PRESSURE - Rawze - 09-24-2026
I keep saying it over and over on here but no one seems to listen half the time ... After-garbage head, after-garbage internals = what does someone expect?. - I have never seen after-garbage components / internals last very long... couple 3 years at best, then cause a huge bunch of expensive headaches.
- If oil touches it then it should be OEM only parts, including the head!.
Sounds to me like it has to be hemorrhaging oil internally somewhere...
My guess .. not seeing it... perhaps a spun a bearing in the trash-can branded head, and no one has noticed it yet?. - It has an after-garbage head on it ... Has anyone bothered to even pull the valve cover off it and crank it up to see if its bleeding oil out of a joint, etc. up top somewhere?.
That, or wrong clearance main or rod bearing?. - Did anyone plastique all the rod/main bearings individually when it was rebuilt?. - or re-checked the clearances recently?
Also,.. is the thing de-mandated?.. (deleted)?.. if so then for all anyone knows it could have hammered a crank bearing or caused some other damage internally. - At the very least.. the programming should be verified that it is not harmful..which means copying program from ecm and e-mailing it to me for a proper review of what someone did in there.
Sounds to me like Someone F%$#KED up somewhere on it, and made a poor decision by using non-OE internals (always a big mistake) 200k miles ago, and now they are paying the price for it .. or it would not be in the situation that it is in. - No way a $40,000+ commercial is going to last a million miles like intended with after-trash parts in it. - At some point its going to cost the truck owner all over again long before those parts pay for themselves.