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Onan 250FT-4R8/2545A High Oil Pressure


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  #1  
Old 11-13-2017, 02:26:23 PM
preskitaz preskitaz is offline
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Default Onan 250FT-4R8/2545A High Oil Pressure

The genset at work is powered by a Cummins GV12-525IPG engine. Theres less than 65 hours on the unit (not bad for a '69 genset where power outages are extremely rare ). Anyways, at some point in time they put SAE 40 oil in her and on the service ticket they noted the high oil pressure. I have since changed the oil to Full Synthetic 10W-30 per the Cummins manual recommendation for our temperature range. I also changed the filters and added a mechanical gauge at the sender. When running the genset the oil is at 115PSI (read from Auxilliary gauge I installed) but the engine temp gauge is normal at 150 and the factory oil pressure gauge pegs out at 100. Is this normal? The longest its run under considerable load was about 1.5 hours when we had a rare power outage because someone tripped the wrong breaker at the substation when they were testing. Even then it ran with no issues. Any ideas what would cause the high pressure? or is that normal for that engine and Onan put too small of a gauge on it?

I forgot to mention they switched to SAE 40 a couple decades ago for some unknown reason.
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Old 11-13-2017, 06:04:46 PM
Jim Marcozzi Jim Marcozzi is offline
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Default Re: Onan 250FT-4R8/2545A High oil pressure

Verify with another gauge. If it's REALLY that high, you may have an oil pump relief valve stuck shut.
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Old 11-13-2017, 09:21:38 PM
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Default Re: Onan 250FT-4R8/2545A High oil pressure

How many GALLONS of oil does the set hold. It can take quite a while, with a load, to bring the oil up to operating temperature. 115 psi sounds too high to me too. Generally..... Cummins engines have the oil pressure relief built in to the area where the oil filters mount. I would research the Cummins manuals for that particular engine to find the normal operating oil pressure. My guess would be 65-75 psi max cold.
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Old 11-14-2017, 02:39:14 PM
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Default Re: Onan 250FT-4R8/2545A High oil pressure

Motorhead about 18 gallons. The oil pressure remains constant even when running at about 150 degrees. I'm looking at the parts catalog for that engine and the oil cooler assembly shows a pressure bypass regulator but unfortunately our oil cooler is not what is shown in the manual. it was noted on an old service ticket I found from 1983 that the oil pressure was at the same as it is now both hot and cold temp. Lucky me I get tasked with maintaining this genset because someone found out I own a few Onan's at home. Then, I find something everyone else dismissed over the years and can't let it go. I'll get some pics up in a little bit.
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Old 11-14-2017, 02:45:19 PM
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Default Re: Onan 250FT-4R8/2545A High oil pressure

See attached pics. The service manual for the engine is more of a maintenance manual and doesn't go into much detail on lubrication system . It does mention that the oil pressure is controlled by a regulator in the oil pump.
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Old 11-14-2017, 03:41:36 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Onan 250FT-4R8/2545A High oil pressure

Isn't that a V-12 1710? Did you happen to cut open the media in the filters when you changed them and look for particles?
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Old 11-14-2017, 04:55:56 PM
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Default Re: Onan 250FT-4R8/2545A High oil pressure

Cummins V12 engine GV12-525IPG. Yeah I opened the filters and they looked normal as in used. This genset has less than 65 hours on it and an oil analysis was done in mid 90's and it came back fine.
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Old 11-14-2017, 06:01:45 PM
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Default Re: Onan 250FT-4R8/2545A High oil pressure

The only way to find out the oil path and where the pressure relief is would be an engine service manual and to find location, a parts manual is quite helpful.
Your best bet is Cummins or find an older Heavy Duty engine shop that might have the manuals. The BEST thing you did was to go to a lighter grade of oil.
With 18 gallons of oil in the system, it will take some time, I'm guessing a couple of hours to bring the oil up to higher than 150 degrees.
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Old 11-14-2017, 07:46:43 PM
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Default Re: Onan 250FT-4R8/2545A High oil pressure

No, not a 1710/VTA28 but its baby brother.

There is an oil pressure relief valve/regulator on the oil pump, need to drop the oil pan to get to it.

I'd leave it alone, the ones I encountered all ran oil pressure in the 100 psi range.

Is there a heat exchanger in the cooling system or is it city water cooled? Run plain water through it? If so, would bet the inside of the engine is pretty much corroded. If there is a heat exchanger, look at the sacrificial anodes be about time to replace them.

I'd be way more concerned about the health of the cooling system than the high oil pressure.
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Old 11-14-2017, 10:30:49 PM
armandh armandh is offline
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Default Re: Onan 250FT-4R8/2545A High oil pressure

if the oil cooler is not stock and
if it is in some way more restrictive
[or some other restriction]
if the gauge is early in the oil flow chart

check oil cooler hoses for an aneurysm like defect
that is ballooning the hose shut internally

the engine may be opening the over pressure bypass
all while the engine is starved for oil

is there a place to measure oil pressure at the far end of the oil galleries
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