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Onan Generators

Oil for Onan Generator


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  #1  
Old 09-09-2017, 01:20:44 PM
TomA TomA is offline
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Default Oil for Onan Generator

I have an Onan Model 4BGEFA26100F Generator out of an '89 Fifth Wheel.

I have never used it much. I had not even started it for 2 years.

During the recent Detwiler Fire our power was turned off for about 48 hours.
I got it running fairly easily and it performed nicely during the outage. I think it benefited from the loaded usage. I had connected the fuel pump directly to the battery in order to prime it.

When I shut it off after the power came on I neglected to disconnect the fuel pump. When I came out the next morning I heard some clicking. I found the connected fuel pump had filled the engine with gas. The cylinders were full and the crankcase was overflowing. I immediately drained the oil, pulled the plugs and dried out the engine.

Thinking I wanted 30W oil I filled it with Traveler 30W Diesel Fleet oil from TSC. The only gas engine oil I had in stock was 10-30. I started engine and ran it briefly, It runs fine.

Now I am wondering if this is suitable oil for the Onan. It seemed to take about 5 quarts which is impressive. If it is not suitable, I can easily drain it and use it in my Cat and replace it with proper oil with no harm done and no waste. My gut feeling is it is good but if anyone has an expert opinion I am ready to change it.

Thanks,

Tom
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  #2  
Old 09-09-2017, 01:57:58 PM
yellowlister yellowlister is offline
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Default Re: Oil for Onan Generator

With that much fuel pumped into the engine I would run it for 10 min not loaded to get any fuel residue out of the bearings than drain it to get all of it out of the oil pan just to be safe. a diesel 30w is ideal or 15 40 diesel oil..
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Old 09-09-2017, 02:03:23 PM
len k len k is offline
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Default Re: Oil for Onan Generator

Manuals specs out what viscosity oil to use for different temps. Haven't run my gens enough to change oil yet.

Manuals are here, site has been down past few days , server issues. they are working on it.
Press link , then when in press control F to search, type NHE, should be at least 4 manuals, service, parts, operator, install. http://www.twinslan.net/~n0nas/manuals/onan/

When these gens sit for months clean genhead slip rings with scotch brite before making AC or $230 AC voltage reg may die. With reg unplugged Onan says clean slip rings if brush to brush is more than 30 ohms. Normal rotor ohms are 20.25 - 24.75 ohms maybe add 1/2to 1 ohm for brush resistance

I've seen ~ 100 ohms after sitting 3-5 months, but I clean slip rings before making AC.

Last edited by len k; 09-09-2017 at 02:27:33 PM.
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Old 09-09-2017, 02:16:45 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: Oil for Onan Generator

If the engine is subjected to temps below 40 F, I would go for the 15W-40, for quicker oil pressure response and easier cold cranking. For summer the 30 Wt is fine. I too would just run for 10 minutes, drain oil and replace filter, to get all the gas out. I would not re-use the oil with the gas contamination. Even if the volatiles dry out (Iso propanes, Iso butanes and alcohols), there are other residues in the gas that remain behind to degrade the oil (toluene, sulfur compounds, additives, etc.). Why take a chance? better to be safe than to be sorry.

Have a look at your carb float and fuel inlet valve. They should have stopped the gas from flooding your engine. You may find a bad float (liquid in it?), worn needle and or seat, or debris in the valve assembly. Is your genset installed level?
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Old 09-09-2017, 02:28:42 PM
len k len k is offline
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Default Re: Oil for Onan Generator

Just looked it up, Paper page 10 of Operator manual 965-0130 specs out what viscosity oil to use for different temps. .

Not knowing any better I'ld run a multiweight oil, so viscosity is about right as temp changes with the seasons just like a car uses. Ei. 10-30, 10-40 or 20-50 depending on what temps run in your area. Have not seen 15-40 here, but I wasn't looking for it.
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Old 09-09-2017, 06:59:40 PM
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Default Re: Oil for Onan Generator

You didn't say if you changed the oil filter. I would do the run for a bit with the oil you put in it and then change it again including the filter.
My question is as to why the fuel pump over powered the needle and seat in the carburetor and flooded out the engine with raw fuel. Is it the original fuel pump? These engines use low pressure fuel pumps, not like what car engines use.
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Old 09-09-2017, 07:26:12 PM
Leon N. Leon N. is offline
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Default Re: Oil for Onan Generator

Good question Motorhead. I have been using 5W20 synthetic in my JB since it became available all year with no problems.
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Old 09-09-2017, 07:56:45 PM
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Jim McIntyre Jim McIntyre is offline
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Default Re: Oil for Onan Generator

Main thing is to fix the carb so the float works, and doesn't allow the bowl to overflow...

I don't think a single person on this site has ever had an engine failure they'd attribute to the oil they chose. So everyone's opinion is always "I use xx brand/weight oil, and it's the best".

That said, if you insist on using a Diesel-rated motor oil in a gas engine, make sure it also carries an 'S' rating for spark-ignited (gas) engines.
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Old 09-09-2017, 08:56:05 PM
AngrySailor AngrySailor is offline
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Default Re: Oil for Onan Generator

Diesel lube oils are generally more alkaline to offset the more acidic byproducts of diesel combustion over gas (TBN or total base number). With todays low sulfur road fuels probably less so. They generally also have higher levels of detergents and dispersants which keep fine particles in suspension relying on the filter to remove. Large diesels often use a centrifuge to remove these fine particles which are impractical to stop by filtration.
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Old 09-10-2017, 10:48:19 AM
TomA TomA is offline
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Default Re: Oil for Onan Generator

Thanks guys for all the replies.
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Old 09-10-2017, 05:28:07 PM
tjc transport tjc transport is offline
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Default Re: Oil for Onan Generator

i run straight 30 in my CCK.
if i run 15-40 it burns about 1 quart every 4 hours. with straight 30 it does not burn any oil at all between changes which i usually do around every 25-30 hours.
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Old 09-10-2017, 08:37:37 PM
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Default Re: Oil for Onan Generator

Quote:
Originally Posted by tjc transport View Post
i run straight 30 in my CCK.
if i run 15-40 it burns about 1 quart every 4 hours. with straight 30 it does not burn any oil at all between changes which i usually do around every 25-30 hours.
I have had engines that do that too.... Go figure?
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