Low Cummins oil pressure

[Al Lewis]

I have he 350 hp ISC engine. I got worried and closely watched the oil pressure on this recent trip. It runs 30 to 40 psi when cruising. At hot idle it gets close to zero. Goes up linerialy between 1000 and 2000 rpm. Much better cold. I switched to the rotella T5 blend a couple years ago. There are two weights of the T5. I thought I got 15W40 but possibly could have been 10W30. The engine never runs hot and I could touch the oil pan without getting burned. What do you think is going on?  Thin oil, guage, or worse like oil pump or bearings. It is about time to change the oil. I will cut the filter open. The engine has 85000 miles.

[Bill Sprague]

On our '04 Monterey the dash gauge was uselessly inaccurate.  The Alladin could not read the sender other than on or off.   I had to decide that if there was oil pressure, it was enough.   The dash gauge was consistent.  For awhile I had a grease pencil mark on it to indicate "normal".

[Doug Allman]

Al, I am not sure if you have the shift panel that we have but if it has D N R you can use this by pushing the D&R buttons at the same time and it will give you a readout in regards to numerous items such as transmission fluid, oil, etc. I do believe that it is mostly on the oil life not pressure.

Now that we have the Entegra with the 600 ISC Cummins I have a contact at Spartan that is very knowledgeable on the Cummins. I am sure he can help you in this regard. However our coach is in AZ and we will not be back there until day after Xmas but if you still need I can get it to you then. Jeremiah goes around the country teaching on the Spartan Chassis and the Cummins power.

Dave Atherton may be able to help you on this also. Put a question in the ASK DAVE section and he can respond.

[Mike Shumack]

IWhat do you think is going on?  Thin oil, guage, or worse like oil pump or bearings. It is about time to change the oil. I will cut the filter open. The engine has 85000 miles.

First thing to do is to put a mechanical gauge on the engine. You can pick up one of these up cheap at an autoparts store with a foot or two of flexible hose.

Like https://www.walmart.com/ip/Auto-Oil-Pressure-Gauge-Engine-Diagnostic-Test-Kit/734351701?wmlspartner=wlpa&selectedSellerId=529&adid=22222222227069541150&wmlspartner=wmtlabs&wl0=&wl1=g&wl2=c&wl3=177050909673&wl4=pla-283656395701&wl5=9011768&wl6=&wl7=&wl8=&wl9=pla&wl10=112354406&wl11=online&wl12=734351701&wl13=&veh=sem

You should not drive any more than you have to until you know what's going on. It could be a mechanical issue (and cheap to fix) like a stuck oil pressure relief spring in the oil pump or just a bad electric sender unit or clogged pick-up screen. But if you keep driving with low oil pressure you could make a cheap fix a very expensive fix.

[Al Lewis]

A little update. I cut open the oil filter and there are no signs of bearing metal. The oil sending unit that Cummins puts on is on the passenger side of the engine block. I have not had an engine warning light show on the dash so I am believing I have a gauge problem. I found two sending units in a T on the drivers side fed by a rubber hose. The front one was coated with oil and dirt. I disconnected the wire and the gauge goes negative. I think this is my problem. I think I found a replacement but have to wait 7 - 10 days for it to be shipped to me. It is listed as obsolete. I will let you know when I get it working.  I did change to the regular T4. 15w40 oil but doubt it made any difference.

[Dave Atherton]

Al, area of concern to look at if your pressure gauge is not the problem. Engine oil cooler
check valve stuck open will cause low engine oil pressure. Dave Atherton Retired Cat Mechanic

[Al Lewis]

I believe I can put this issue to rest.  I did not have an oil pressure problem just a gauge issue.  I finally found an equivalent oil pressure sender unit and replaced the old one.  Now the gauge indicates 100 psi at start up.  After a short run to the fuel station and back, it looks like I will have about 70 psi cruising and 20 psi at hot idle.  This is probably correct.

I believe the old sending unit was leaking oil past the diaphram causing back pressure equal to the hot idle pressure. If I had drilled a hole in the back to let oil out I could have proved or disproved this theory.  I did not do that.  I replaced it.

The sender is just a variable resistor.  At zero pressure the old one measured about 250 ohms.  My auto parts store found one they thought would work but resistance was low, about 15 ohms.  I tried it and the gauge pegged when I turned the ignition on but would come down to around 70 psi after engine start up.  Scrap that $45.

I called Beaver Sales.  They had a unit for $65 (plus shipping I guess) with a part number 16617200. That part number must be a beaver or monoco number since it did not show up on the internet.  I found on ebay units labeled as 100 psi with 240-33 ohms resistance.  I ordered one at $19 that included shipping.  I installed it and got good results.  It carried the name of Datcon.  It had a low pressure alarm terminal also but I did not use that.

The unit I replaced was on the forward side of a T-block.  Another sender unit was screwed into the backside of the block.  I don't know what that does.  If anyone knows, please tell me to satisfy my curiosity.

[Roy C Tyler]

Al, the numbers you quoted for pressure are exactly what I get on my Cummins.