Engine/Transmission (1998.5 - 2002) question regarding oil pressure issue on 99 ISB

[jturuk]

Hello all

I need to verify the oil pressure on this engine. There is what looks to be a 1/8" plug on the top of the oil filter head beside the braided line that goes to the turbo. Can I hook up a guage to this port and could someone confirm the thread size as 1/8 " NPT?

Thanks

John

 

[CM_Guest]

Yes, you can read oil pressure there and it is 1/8 NPT. If I remember correctly, that is oil pressure "downstream" of the oil filter - i.e. after the oil has passed through the filter media. I'm not sure what "spec" is but I've seen up to 100 psi there on a 1st-gen 12V with warm oil at high idle. Warm being after a few minutes of idling vs. hot after extended operation. A good "minimum" rule of thumb for oil pressure is 10 psi per 1000 engine rpm with the engine completely warmed up. But that is lower than I like to see the oil pressure in engine. But there is also such a thing as excessive oil pressure. Personally, I think Cummins B-series engines run excessive oil pressure and waste a lot of power and fuel doing it. 60-100 psi is too much. 50 psi at high idle with hot oil is more in line with what most medium-duty and heavy-duty diesels run at operating temp and full load. No doubt some "knowledgeable" people will take exception to that, but that's been my experience wrenching on diesels for 20 years. Diesels have large bearing areas for a reason and it's unnecessary to have sky-high oil pressure AND large bearing areas to carry the load.

 

[jturuk]

Yes, you can read oil pressure there and it is 1/8 NPT. If I remember correctly, that is oil pressure "downstream" of the oil filter - i.e. after the oil has passed through the filter media. I'm not sure what "spec" is but I've seen up to 100 psi there on a 1st-gen 12V with warm oil at high idle. Warm being after a few minutes of idling vs. hot after extended operation. A good "minimum" rule of thumb for oil pressure is 10 psi per 1000 engine rpm with the engine completely warmed up. But that is lower than I like to see the oil pressure in engine. But there is also such a thing as excessive oil pressure. Personally, I think Cummins B-series engines run excessive oil pressure and waste a lot of power and fuel doing it. 60-100 psi is too much. 50 psi at high idle with hot oil is more in line with what most medium-duty and heavy-duty diesels run at operating temp and full load. No doubt some "knowledgeable" people will take exception to that, but that's been my experience wrenching on diesels for 20 years. Diesels have large bearing areas for a reason and it's unnecessary to have sky-high oil pressure AND large bearing areas to carry the load.

Thanks kindly for your reply CJMEYER. The oil pressure guage went to zero when my wife was driving the truck and then she said that it started fluctuating. The engine isn't knocking or rattling so I'm thinking/hoping that it is just the sensor. I just wanted to find some spot on the engine where I could confirm that I do indeed have oil pressure.

John

 

[CM_Guest]

You're welcome and I hope you find good oil pressure there. A known good mechanical oil pressure gauge is the first tool to reach for when diagnosing oil pressure issues. I suspect you just have a gauge circuit problem. More than a few few seconds of true zero oil pressure with a warmed up engine under any kind of load will definitely do serious damage so if it's still running you're probably in the clear. With any sort of so-called factory "gauge" or idiot light by the time the "gauge" hits zero or the light comes on, it's probably already too late. Why so many guys are obsessed with filling their cabs with aftermarket gauges for everything BUT engine oil pressure is beyond me, given how unreliable and inaccurate factory in-dash "gauges" actually are.