Engine/Transmission (1994 - 1998) Oil Pressure

[EBottema]

Having a little trouble with my Dad\s 96 12v. Has approx 210k on the clock.

Lately the oil light has come on and pressue had dropped at stop signs. Happened twice but when you rev it up, the light goes off. I figured a bad oil pressure sending unit. Installed a new one yesterday and the reading looks less erratic than before. However, above idle, the oil pressure gauge reading approx 40psi, at idle only about 20psi right about the low end of the acceptable level on the gauge. My 12v reads 40psi at idle and 50 at normal rpms. Anyone have any idea what the problem might be? Worn out oil pump?



Thanks

erik

 

[Joe G.]

Is his idle too low?



For a proper check of the oil pressure you might T a mechanical oil pressure gauge with the stock sending unit and see if they agree. You would want to rig the mechanical gauge so you can see if from the cab. I prefer to test both pressures at the same place instead of putting the test for the mechanical gauge at the oil filter.

 

[bmoeller]

As Joe said, a mechanical gauge to verify the PSI, would be a good idea. 20# (warm oil) doesn't sound all that bad, at idle. IIRC, the general rule is you want 10 PSI for every 1000 RPMs.



My FSM says a MINimum of 6PSI at curb idle speed. MAX of 30-80PSI @ 3000RPMs+.

 

[JFaughn]

If your oil pressure testing , according to the above methods show low oil pressure the 2 ideas come to mind are oil pump or rods and main bearings , have the oil tested and that would help to point you in the right direction , other wize you can take the oil pump apart and check for wear and scoring , if that checks out then measure a couple of bearings , if they have not warn through the babit [ the silver looking coating and not into the brass looking] you can replace the rods & main bearings , if you find badly warn bearings then the crank is out of round and the bearings wil not last, I haven't done it yet in one of these trucks yet but most of the time its a connecting rod thats out of round then what I've done a lot of is put in a used [ that checks out ] crank and pull the piston out and back in the bottom to change the rod, in the old days this was done a lot with passenger cars & trucks now its just done with big rigs , its called inframe work. thats if you do your own work , a shop may not be willing to do it that way .

 

[biggy238]

Do a search on it, I posted when I first bought my truck and soomeone pointed out to me that there is a mechanism on the pass. side of the block that helps control and regulate the pressure. It's spring loaded and the spring could have weakened. (I hate to call it by name since I don't remember how it works)

 

[Joe G.]

Kyle,



It's a pop off valve used to avoid extra high pressure. A mechanical oil pressure gauge will still show a start up pressure spike that can be as high a 80 PSI. This problem is low pressure. He is still showing 40 PSI on the road so I doubt the spring is so weak as to cause 20 PSI at idle. It's important to verify that the pressure shown on the stock (can be unreliable) guage is true.

 

[EBottema]

I will be hooking up a gauge this week and checking it.

The truck is an auto and the idle seems fine.

I changed the oil last week with the regular Delo that he always used. When the pressure is around 20psi, it is hot over 100 degrees up here and has been running for minimum 15 minutes. Truck runs great otherwise. Stock engine minus EGR and AFe filter. . I have the oil from the filter in a ziploc baggy, should i get a cummins oil test kit and post the results? Who do i get those from, approx how much?



Thanks

erik

 

[btbuchanan]

I have been having the same problem. Changed the sending unit, but the problem came back in a couple of weeks. Have put a mechanical guage on the oil filter housing, and when the "check guages" alarm goes off and the in-dash guage show s zero pressure, there is still actually 25 psig at the filter housing. Happens more and more lately and others have suggested that I should reflash the ECU(M) since the guage signal goes through the ECM(U). That's next for me.