350 ISC oil pressure gauge help

[wingtrike]

The oil pressure gauge goes to 45. It just stays there. My dealer tried a new oil pressure sending unit but it didn't stop the problem. We are thinking it could be a bad connection. Where to start? I am thinking start at the oil pressure gauge itself then go from there. When you turn the key off, all the gauges go to zero.
Then engine runs fine with no apparent problems. I did have the dealer change the oil and filter plus the fuel filter before they tried a new sending unit.
I would like to solve this myself without taking the coach to a Cummins dealer.
Any and all advice would be appreciated.

Thanks,
Alex

[PandK]

There was a similar thread a fw weeks ago. It "appears" the ECM put out either a "1" or a "0" for oil pressure. Therefore you either see some number (ie 45psi, I see 65 psi) or the gauge goes to zero.
That is consistent with what I see with my Silverleaf unit.

[wingtrike]

The gauge does not move when revving the engine to 1500-2000 rpm. We have tried putting the coach in gear with the parking brake on. Shouldn't the gauge move when under load????
Thanks,
Alex

[PandK]

Check out this (Concerns over oil pressure indication on an ISB) thread. It says ISB but several replies are from people with the ISC. Same concern as yours and is "apparently" the way Cummins designed the ECM output. I'll put the oil pressure on my VmsPC and see what data it logs next time I'm out just to satisfy my curiosity.

[stuhly]

Three or four years ago Cummins had a bunch of bad Oil pressure senders that registered actual pressure. They had a lot of problems them. Cummins then changed to a simple on - off type sender. They had to reprogram the computer after the install. You either have pressure, around 45 to 65 lbs or you do not - 0. The needle does not move up or down with RPM. Went thru this with my 2000 Discovery with Cummins.

[AFChap]

Mine was originally variable, but went berserk while driving in '04 with flashing lights and emergency shut-down warning bells and buzzers. After sitting on the side of the road for a couple hours while Coach-Net searched for a large enough wrecker, I turned the key back on and everything was normal. It had re-set. I drove it to the cummins location and the sender was replaced/reprogrammed to an on/off under warranty.

Most cars/pickups etc now have on/off type senders even when they have variable capable needle When I complained about my guage not showing actual pressure on a 97 Ford, they told me the mfgers had gone to on/off type due to too many warranty claims and wasted appointments with people who did not understand variable guages and insisted something was wrong with the vehicle Rather than educating the buyer, they dumbed down the vehicles.

[powerboatr]

my 08 isc oil pressure gauge moves up and down slightly with engine rpms and temps.
not much but it does move around

[RV'nOldTimer]

My vmsPS aways read "45" with the engine running and "0" when off. After figuring out, with help from this forum, that the "45" was a proxy for "everything is OK" and not a real numeric indication, I changed the dumb thing to only show a red light if the indication is bad. As others have said, its a dumbing down for the customer.

I'd bet your's is the same.

JT

[dons2346]

Some coach mfgs install a separate oil sending unit for the dash gauge. These are a Cummins part and during the 2000-2002 time frame there were some bad ones which would cause the engine to derate and eventually stop. There was no set pattern as to when or if the sender would go bad. I have been lucky and my engine built in 2001 still has the original sender. The replacement is a unit that will give you 50psi all the time so basically it is an on/off switch. Any variance from this is probably due to the calibration error of the gauge installed.

Then there is another sender unit installed by the engine manufacturer. THIS is the one you should be concerned about as it feeds info to the ECM and is responsible for shutting the engine down in case of low oil pressure. If you have a Silverleaf installed, it gets its info from the ECM and not the dash sender unit.

A Cummins rep said that low oil pressure is of no real concern with their engines.

I use the dash gauges for amusement purposes only and rely on my Silverleaf.

[wingtrike]

Thanks so much for the info. Y'all have been very helpful.
Oil pressure safely,
Alex

[spike45]

Quote:

Originally Posted by wingtrike The gauge does not move when revving the engine to 1500-2000 rpm. We have tried putting the coach in gear with the parking brake on. Shouldn't the gauge move when under load???? Thanks, Alex

Engine oil pressure is not dependent upon loaded or unloaded conditions. Pressure is governed by the pump relief valve. All oil pumps produce greater volume than the engine can handle. The relief valve opens to limit the pressure. Most Cummins engines have oil pressures in that range of 45 to 50 PSI. They have not gone higher like some other engine brands. Even the 15 liter ISX only runs 45 PSI. If the oil pump has some wear or the engine is older, the oil pressure will drop some at idle but not alot until the pump has more significant wear or you have more internal wear in the engine bearings. The task for the oil pump is to pump more oil than the engine can internally leak at any given time. By producing more oil than internal leakage, the pressure is maintained. When the internal leakage rates are high enough and the pump has sufficient internal wear, the overall oil pressure will drop and have much greater swings in pressure from idle to high idle.

The problem with most vehicle gauges is that they are not test instrument quality. If the needle moves at least you know the engine is running! Surely you have noticed some gauges just a line between L and H but no specific niumbers. That is because gauge quality varies greatly. Get quality manual gauge and test the pressure, not an electric sender unit type. Verify the oil pressure.