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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
preskitaz preskitaz is offline
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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
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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
preskitaz preskitaz is offline
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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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Old 11-14-2017, 11:01:54 PM
MBB MBB is offline
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Default Re: Onan 250FT-4R8/2545A High oil pressure

Here is some information on the unit. I though I had a manual but I guess not.
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File Type: pdf 250FT4R82545A.pdf (35.7 KB, 19 views)
File Type: pdf 612-1798.pdf (186.0 KB, 13 views)
File Type: pdf 612-3493.pdf (235.6 KB, 12 views)
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Old 11-15-2017, 01:06:37 AM
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Default Re: Onan 250FT-4R8/2545A High oil pressure

Agree with Gunny, the oil pressure's fine, and as you stated hasn't differentiated in years according to records. I remember the old six cylinder NH220's (743CID) and the NRTO6's in our old military gensets used to always be around 100 psi when first started--more if it was winter. Somewhere about the time engines such as these and yours were being succeeded, the engines thereafter seem to be more consistent at holding starting oil pressure in the 90's. (just some observations over the years.)

I am more curious as to who would have said to run 10W30 in it though. Cummins oil Spec CES20074 is very likely the spec (its been around for a quite a while) that engine would fall under. Under this spec, as OEM oil, Cummins uses Valvoline GEO oils, in 5W40, 15-W40, and straight 40WT. There is no 10W30 gas spec'd oil endorsed by Cummins that I'm aware of. [how cold does it actually get in that room?]

These oils are have lower specific ash contents specs, and higher alkalinity when new, to combat the acids that accrue at a more rapid rate in gaseous engines than diesels.

What is the synthetic oil you're currently running? Since this is stand-by use, and likely getting changed yearly, acid build-up, nitration, oxidation, etc, are not likely to be issues. These concerns are very valid, however, for over-the-road gaseous engines, and stationary prime and part time power units.
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Old 11-15-2017, 12:22:01 PM
preskitaz preskitaz is offline
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Default Re: Onan 250FT-4R8/2545A High oil pressure

Quote:
Originally Posted by armandh View Post
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

is there a place to measure oil pressure at the far end of the oil galleries
The cooler is an OEM setup for the cooling system we have (total waste City water cooled). The Gauge I installed is on the other side of the block from the cooler on a tee at the sender location. I don't have a shop manual to determine exactly where in the path it gets its measurement.

MBB, You do have all the manuals and brochures for this unit. I sent them to you a while back for the twinslan site. 960-81,960-10,
960-11
960-10
960-11 960-81.


Eric, see attached Cummins service bulletin . The vault it sits in is below grade and ambient is usually 40+ degrees but may dip below 40 but stay above 32 during winter months.
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Old 11-15-2017, 03:23:20 PM
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Default Re: Onan 250FT-4R8/2545A High oil pressure

Your right. I believe Doug hasn't had a chance to post them yet. I didn't put them in my list. Thanks for reminding me.
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Old 11-15-2017, 04:07:07 PM
len k len k is offline
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Default Re: Onan 250FT-4R8/2545A High oil pressure

Mechanic I know had a oil filter can split open, he replaced it and that one split open too. Turned out the oil pressure by-pass valve ( regulator) in oil pump was stuck shut and pressure was skyrocketing. Don't know the presure it made. But if knew how thick the filter can was and it's diameter I could make an estimate on what it takes to burst it.
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Old 11-15-2017, 06:30:00 PM
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Default Re: Onan 250FT-4R8/2545A High oil pressure

Just my 2˘

I just ran one of these engines on a Kohler unit of the same vintage this morning. My unit still has the original Cummins engine metering cluster in place on the front left of the engine. Note in the picture that the Cummins oil pressure gauge reads up to 150 psi.
During a two hour loaded run the oil pressure never dropped below 105 psi (according to the gauge). Oil temp came up to about 190* by the end of the two hrs. Note that my unit only had about a 40% load for the duration of the run. We use the Cummins GEO 15w-40 oil.
I would not be concerned.

On a somewhat related note. I've got a GTA38 at another site that makes 105 psi + on start up. The power command controller goes into warning with anything over 105. After a few min the oil temp comes up, oil pressure drops a few psi to around 91-96 psi and the warning clears. I had a conversation with Cummins Natural Gas in New Mexico about the situation. They informed me that the maximum allowable oil pressure spike in a cold starting situation was 220 psi for that engine.
I am not concerned with this one either.
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Old 11-15-2017, 09:42:17 PM
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Default Re: Onan 250FT-4R8/2545A High oil pressure

Can't beat comparative, actual information from another like engine. /\
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Old 11-16-2017, 07:05:06 PM
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Default Re: Onan 250FT-4R8/2545A High Oil Pressure

That oil cooler looks OEM to me.
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Old 11-17-2017, 11:58:21 AM
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Default Re: Onan 250FT-4R8/2545A High Oil Pressure

It is OEM but not whats in the parts manual for the engine. (See the link on my previous reply)

---------- Post added at 07:58:21 AM ---------- Previous post was at 07:53:55 AM ----------

Quote:
Originally Posted by preskitaz View Post
It is OEM but not whats in the parts manual for the engine. (See the link on my previous reply)
I also found out that the large tank at the front is possibly the heat exchange. I spoke with my co worker who repaired a leak on it said there's a coil inside. I don't have much literature in the way of this particular cooling system but I would assume there is glycol solution in the closed loop system? I was also told there are sacrificial anodes on the engine as well and they were checked about 5 years ago.
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Old 11-17-2017, 08:14:51 PM
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Default Re: Onan 250FT-4R8/2545A High Oil Pressure

Be a real good idea to change out the coolant, probably pretty old. I may never loose its ability to protect from freezing but the anti corrosion protection depletes in a relatively short time. Causes things like liner cavitation, rust and corrosion.
Yes, find and change out those sacrificial anodes, probably more than 1 or 2. Made out of zinc. When I did service, I'd pull them out annually and measure them, use a marker and record the length along with the date near the anode(s)

Be a real good idea to change out the coolant, probably pretty old. It may never loose its ability to protect from freezing but the anti corrosion protection depletes in a relatively short time. Causes things like liner cavitation, rust and corrosion.
Yes, find and change out those sacrificial anodes, probably more than 1 or 2. Made out of zinc. When I did service, I'd pull them out annually and measure them, use a marker and record the length along with the date near the anode(s)
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