Oil Pressure Question

[RV'nOldTimer]

I recently installed a VMSpc and have been watching the various readouts. Its curious that my oil pressure always indicates 55 psi, hot, cold, idle or at speed.

Does this mean the signal is an on/off only or is my pressure truly 55 psi under varied conditions?

Cummins 5.9 300hp

JT

[dons2346]

I believe so. On some engines, Cummins had a problem with faulty pressure switches which would cause the motor to shut down. They then went to the "on or off" type. Those will show 55 pounds.

A call to Cummins will verify this.

[Gary RVRoamer]

Yeap - it's either "OK" or "Not OK" and OK is defined as a 55 psi reading. My Trip Tek dash computer/display shows the same 55 psi reading off the engine bus.

[RV'nOldTimer]

Quote:

Originally Posted by Gary RVRoamer Yeap - it's either "OK" or "Not OK" and OK is defined as a 55 psi reading. My Trip Tek dash computer/display shows the same 55 psi reading off the engine bus.

Thanks guys.

In that case I'm gonna reset the display for a warning display only and save a little geography for other things on my screen. I don't need to see a meaningless number when a red or green "ok" or "not ok" will give the same information!

JT

[powderman]

I can't speak to a motorhome, but the oil pressure in a Cummins dodge Ram is just something the computer makes up. They did this to offset fears of people who were concerned to see the actual oil pressure show as low as they often run at oil pressure much less than what people are accustom to seeing. So now if the oil pressure is enough that its not a concern, they make it show a higher number. It could be they are doing the same in RVs. Just go to a dodge diesel forum and search oil pressure and you will find lots of posts.

[Ann n Gene]

Oh GREAT! Another company not respecting their customers by telling the truth. No one wanted idiot lights so they just change to a lying readout. If I had wanted idiot lights, thats what I would have bought. I EXPECT guages to be accurate (they are on my ISM, I have checked them). It IS true that the newer engines are designed to run lower oil pressure than what used to be the case but come on manufactures, tell us what normal is for your engines, then put accurate guages in so that we can accurately tell what our expensive engines are doing. just my rant for the day.

[dons2346]

It is not the engine mfg that puts the gauges in the coach, it is whoever put your coach together. What you will find is one pressure switch the feeds the gauge on the dash and another that feeds the ECM. It is the ECM that you should be worried about but either one can be tied to the "shut the motor down" red light. Cummins has said, (in an FMCA seminar) that 10 pounds of oil pressure is fine at idle. Normal pressure at cruse RPM is 50-55.

[AFChap]

Quote:

On some engines, Cummins had a problem with faulty pressure switches which would cause the motor to shut down. They then went to the "on or off" type. Those will show 55 pounds

Yep ...that's what they put in my 350hp 8.3L ISC under warranty after we got all kinds of clanging bells and flashing lights while driving down the highway when the coach was about a year old ...I much prefer a real gauge, but am pretty used to fake gauges as most cars/pickups/SUVs now days that have gauges don't have variable senders on them.

[Triker56]

With the VMSpc the older ISB's give correct Oil PSI and changes from idle to speed.

I can't tell you what year they changed that.

[RustyJC]

A digital readout of engine oil pressure (among other operating parameters) is available on my truck's EVIC (electronic vehicle information center), so not all ISBs have a "fake" sending unit. My 2002 ISB utilized an oil pressure sending unit as opposed to a switch as well.

Rusty

[dons2346]

A call to Cummins will get you a range of serial numbered motors that were affected by the bad oil sending units.