Starting about a year ago my 7.5 KW diesel generator on about every 3rd start attempt would start and run for about 5 seconds and then auto shutdown flashing a low oil pressure code. This only happened about a third of the time and only on start up. Once started if it didn't shutdown after 5 seconds it ran normally. It never shut down after a successful start. I changed the oil and filter and topped the oil right up to the top of the oil dip stick. This worked for about 6 months and then started again. I over filled the oil by about half a quart and again that seemed to fix it for about a month or about 10 start attempts before it happened again.Now it happens about half the time. It starts and runs for about 5 sec and displays 2 flashes on the start switch indicating a low oil pressure issue. But again when it does start successfully it never auto shuts down, ie it runs until I manually shut it down. So it is an intermittent issue.It is impossible to get to the oil pressure sending unit without virtually taking the entire engine apart. I would like to verify the engine is getting oil pressure. I can get to the white wire leading to the pressure switch and am wondering if I can verify oil pressure in some way by testing the wire to the oil pressure switch. Any help is greatly appreciated. I've been chasing this problem for almost a year.

My Cummins/Onan dealer is VERY helpful.If you have one nearby, a visit to them likely would yield some useful information.The two I have experience with are very picky about oil LEVEL......such that parking on a slight incline can cause a "low oil" failure.I've been filling mine up until you can't put in any more, which is only a couple of ounces high, and that seems to have solved that problem for me.

check the wiring to low pressure oil switch. Is switch one wire or two? Normally switch is open until low pressure or higher then closed. If engine sounds ok when running it is probably the switch.

One wire to the low oil pressure switch, it is white. Engine sounds and runs normally.

Overfilling can cause churning and foaming of the oil, which can mislead the pressure sending unit into thinking there is no oil.Make sure it is not over-filled also.Steve

maillemaker wrote:Overfilling can cause churning and foaming of the oil, which can mislead the pressure sending unit into thinking there is no oil.Make sure it is not over-filled also.SteveWhile I understand that they might not all be the same......the ones I've seen it is impossible to overfill them to any significant degree. A couple of extra ounces certainly will NOT cause the doom and gloom that you described.

Onan Generator Fault Code 2- Low oil pressure | Good Sam Community

Sam_Spade
Explorer
Nov 11, 2019
My Cummins/Onan dealer is VERY helpful.
If you have one nearby, a visit to them likely would yield some useful information.

The two I have experience with are very picky about oil LEVEL......such that parking on a slight incline can cause a "low oil" failure.

I've been filling mine up until you can't put in any more, which is only a couple of ounces high, and that seems to have solved that problem for me.
alaska_dennis
Explorer
Nov 11, 2019
check the wiring to low pressure oil switch. Is switch one wire or two? Normally switch is open until low pressure or higher then closed. If engine sounds ok when running it is probably the switch.
timjet
Explorer
Nov 11, 2019
One wire to the low oil pressure switch, it is white. Engine sounds and runs normally.
maillemaker
Explorer
Nov 11, 2019
Overfilling can cause churning and foaming of the oil, which can mislead the pressure sending unit into thinking there is no oil.

Make sure it is not over-filled also.

Steve
Sam_Spade
Explorer
Nov 11, 2019
maillemaker wrote:
Overfilling can cause churning and foaming of the oil, which can mislead the pressure sending unit into thinking there is no oil.

Make sure it is not over-filled also.

Steve

While I understand that they might not all be the same......the ones I've seen it is impossible to overfill them to any significant degree. A couple of extra ounces certainly will NOT cause the doom and gloom that you described.
timjet
Explorer
Nov 11, 2019
It may be over filled slightly but that's not the problem. It initially started a year ago when it was slightly below the fill mark on the dip stick. I changed the oil and filled to the top of the dip stick and that seemed to fix it for about 6 months then started again. Also note that this only happens on start up, it has never shut down once it has started successfully until I purposely shut it down.
cbr46
Explorer
Nov 12, 2019
What oil viscosity does the manual recommend?

Try a thinner viscosity oil (first #). ie 5w30 vs 10w30. My Honda portable has the same problem, more so when it's cold out. Once it's running a few minutes it's good for the weekend.

I run a Honda 2000 because it uses 1 gal / 8+ hours vs the genset at 0.5 gal / hr. And I never hear it running.

Best,
- bob
alaska_dennis
Explorer
Nov 12, 2019
This sounds more like air intrusion in the fuel.
"Now it happens about half the time. It starts and runs for about 5 sec and displays 2 flashes on the start switch indicating a low oil pressure issue. But again when it does start successfully it never auto shuts down, ie it runs until I manually shut it down. So it is an intermittent issue."
bounder39zman
Explorer II
Nov 12, 2019
the oil pressure switch on that unit is a NC type switch, and it is "closed " to ground with no oil pressure. the switch "opens" on rising o.p., (about 7-9 psi) . The switch is indeed difficult to access without being able to remove top and side panels from set. these switches dont usually fail on an intermittent basis, but is possible. I have more problems with leaking than not working correctly. Not likely to be a problem with oil pump pick-up, as it happen on every start-up, and Kubota's quality control is very high. Possible that there is moisture/corrosion in wire harness connector to Inverter-controller, shorting out oil switch wire...I've run into this before. Would advise not to overfill oil level very much, as previous post said, that can cause oil to churn and foam in crankcase, tricking switch to close.
Sam_Spade
Explorer
Nov 12, 2019
timjet wrote:
I changed the oil and filled to the top of the dip stick and that seemed to fix it for about 6 months

Gotta ask.....are you assuming that it is still "full" of oil, or did you actually check it ?

Is it parked on a hill ??

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Onan Generator Fault Code 2- Low oil pressure

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