erratic oil pressure gauge

[rambler05]

We have a 05 HR Neptune with a 300 Cummins. We have experienced an erratic oil pressure gauge. On a 400 mile driving day the oil pressure gauge indicated 120 psi. We stopped and when engine was in idle the pressure returned to normal around 60. When we started again it peaked and then bounced between 60 and 120. Seems like a defective gauge or bad wire. Everything was running smoothly. We will call Cummins, but are wondering if anyone has experienced this problem?

[RustyJC]

Quote:

Originally Posted by rambler05 Seems like a defective gauge or bad wire.

More likely a bad oil pressure sending unit.

Rusty

[Flagelpater]

FWIW One symptom of a bad gage is for it to Not go to zero when it should. My boost gage failed this way. Made it real simple to determine if it was a bad sensor or gage. Is there moisture, like rain, involved?

[rambler05]

We were returning to So. CA from AZ and we did have a few weeks of off and on rain. Not like CA though. It was dry and in the high 60's on the drive home.

Rambler 05

[rambler05]

Thanks for your input.

[tom wilson]

have had erratic oil pressure readings and it was always the oil pressure sender. have replaced it twice in 14 years. get it from spartan for $40.00.

[rambler05]

Thanks for the info. Really appreciate all the response.

[Mike Canter]

You might first verify that the connection to the oil pressure sensor is clean and tight.

[Robi.1014]

Feedback so far seems to be right on WRT troubleshooting. But what I picked up on was your reported readings. FWIW, my dash oil pressure meter's max-scale is 120, but when the engine is at running temp, the gauge never reads above 60. At idle, the gauge reading falls to approximately 10 (the gauge only has zero, 60 and 120 reading marks). I was alarmed at this low reading initially, so I broke out the Cummins Operation & Maintenance Manual and found:
- 10 is the minimum allowable at low idle
- 30 is the minimum allowable at rated speed
- 75 is the "regulated pressure".
I'm guessing that my 04 Dip Cummins ISC-315/330 is basically the same as yours, so your reading of 120 sounds like an erroneous reading from the git-go.

I'd be interested in hearing others offer comments on their observed meter's readings.

[WindsorDave]

Quote:

Originally Posted by Robi.1014 ...so I broke out the Cummins Operation & Maintenance Manual and found: - 10 is the minimum allowable at low idle - 30 is the minimum allowable at rated speed - 75 is the "regulated pressure". I'm guessing that my 04 Dip Cummins ISC-315/330 is basically the same as yours, so your reading of 120 sounds like an erroneous reading from the git-go. I'd be interested in hearing others offer comments on their observed meter's readings.

My ISC 330 engine oil pressure gauge appears to be solid and working predictably. Upon start-up while the engine is still cold, pressure will be somewhere around 30 PSI at idle, depending on initial ambient temperature. It then decreases as the engine temperature rises.

Once the engine is up to 180*, normal operating temperature, oil pressure at idle drops to around 10-13 PSI. At normal operating temperature the oil pressure is consistently at 60 PSI when the engine is in the normal 1,400 to 1,800 RPM operating range. It goes down a little when water temps start approaching 200* climbing hills in hot weather. But I've never seen it go below ~50 PSI under those conditions.

My gauge also has a coarse scale with tick marks at 0, 30, 60, 90, and 120 PSI so all of the above readings are necessarily approximate.

I'd be interested to hear what others have observed on their transmission oil temperature gauge while operating their coach. Mine does not move except during a "stall" test - i.e. putting it in Drive, depressing the brake pedal, and revving the engine. Even then it only goes up a little.

FWIW

[Robi.1014]

Dave:
"I'd be interested to hear what others have observed on their transmission oil temperature gauge while operating their coach"

My tranny temp meter-reading never reaches even 140. I got it higher one day as you did: kept the brakes on and went to high idle for some 10 minutes....at which time the tranny-temp meter got just above 140.

Once I tried the diagnostic mode on the Allison control panel, and (if I recall correctly), some of the diagnostics would not read back to me, citing an error code something like: "transmission too cold".

[WindsorDave]

Quote:

Originally Posted by Robi.1014 Dave: "I'd be interested to hear what others have observed on their transmission oil temperature gauge while operating their coach" My tranny temp meter-reading never reaches even 140. I got it higher one day as you did: kept the brakes on and went to high idle for some 10 minutes....at which time the tranny-temp meter got just above 140. Once I tried the diagnostic mode on the Allison control panel, and (if I recall correctly), some of the diagnostics would not read back to me, citing an error code something like: "transmission too cold".

Robi,

Interesting. Maybe this should be a different thread. But in the mean time - beyond checking the oil level via the control panel, I have not tried the diagnostic mode. That said, the oil level function works as advertised. If the oil is too cool or has not settled following a period of driving the coach, the transmission knows and relates that information to the control panel with the appropriate error code or count down (settling time).

That indicates that a temperature sensor/sending unit is functioning, which begs the question - are there different sending units that drive the dash gauge and the TCM (transmission control module)? In a nod to the original thread subject, engine oil pressure indications, the same question pertains. Are there different sending units for the dash gauge and ECM (engine control module)?

I'd really like to resolve this since we do a fair amount of mountain driving and I don't want to unnecessarily burden the transmission. I'm learning to manage engine water temps on long climbs by manually gearing down and keeping turbo boost at or below 25 PSI. It would be good to know how the transmission reacts to the various inputs.

Still, I hate to take it in to a shop without more concrete, quantifiable symptoms. Trouble shooting (trouble-guessing?) at $100+ per hour can get expensive.

[Mike Canter]

Dave, if the Allison Sump Temp Sensor has failed then you would get a trouble code #33 if you ran the keypad diagnostics. You need to run the keypad diagnostics.

[Whitofok]

My coach has had the same erratic pressure readings as rambler5. The oil pressure has been checked and is correct. Need to find out and get corrected. Let me know if anyone gets the solution
Thanks