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Old 11-10-2011, 05:57 AM   #1
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Generator Oil

I am planning to change the generator oil on our Onan 7000 (gas). It has approx 120 hours on it. The last change the shop used Onan 15W40 oil. I plan on using a major brand of oil, 15W40, but not Onan since I would have to drive about 40 miles from where I live to buy Onan oil. I do have an Onan filter which I will use. However, I am wondering if I should change to a synthetic or a synthetic blend. We don't use the generator much but I do follow Onan's recommendations and exercise the generator monthly. Since all has worked well so far I probably will stick with just the regular oil but will appreciate comments on changing to synthetic or a blend.


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Old 11-10-2011, 06:29 AM   #2
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I use dino oil in ours because, like you, we use our generator very little - mostly running it an hour or 2 a month for exercise as stated in the owner's manual.

Onan recommends changing oil every 150 hrs or once a year, whichever comes first. Since we use the genny less than 20 to 25 hrs a year, I'm always changing oil by time instead by number of hours used. I know synthetic will cut down friction and wear, but I figure why go to the expense of synthetic if the genny doesn't even get used that much.

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Old 11-10-2011, 07:04 AM   #3
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I have been told Onan does not recommend synthetic oil. I always have used a regular brand 15W40 and never any problems.

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Old 11-10-2011, 07:49 AM   #4
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Originally Posted by Petro View Post
I have been told Onan does not recommend synthetic oil. I always have used a regular brand 15W40 and never any problems.

Have always used Rottela 15-40, works for me and is an excellent oil.
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Old 11-10-2011, 09:52 AM   #5
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Another Rotella 15W-40 user here as well... You can pick it up at your local Wal-mart...
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Old 11-10-2011, 10:08 AM   #6
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My Onan / Cummins dealer whole heartedly recommended synthetic oil. Don't ever assume Dino oil is better, because it just isn't. This is especially true in a generator where the oil sits for indefinite periods. As soon as you run your generator for that first exercise cycle your Dino oil begins to breakdown and becomes contaminated with combustion products. Synthetic oil is consistent with its molecular structure and way less prone to loss of lubrication and viscosity. In addition to this, synthetic will protect at higher temperatures. Like those in motorhomes and generators specifically. Generators can be temperamental, give them the best.

I change mine annually with Rotella 5W-40.

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Old 11-10-2011, 10:15 AM   #7
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I use 10/30w. What Onan Recommends, I usually buy Motorcraft Oil. Not Dino oil, the Semi-Synthetic. Usually change it once a year, I have solar and really the only time I run the Generator is if I need to run the Air Conditioner.
We only have 225 hrs on it, in 6 years.
Buy it at Wally World.

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Old 11-10-2011, 01:17 PM   #8
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Some posters may have missed the comment that this is a gas generator. I would do lots of research to see if it's okay to put diesel oil in a gas engine...the majority (that I have seen) say no.
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Old 11-10-2011, 01:49 PM   #9
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I use oil made for air cooled motorcycle engines. Since it is a air cooled engine.
Mostly ran just to exercise it. Only change it every 3 years. Oil still looks like new then running on LP. And still way under the 150 hours.
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Old 11-10-2011, 02:23 PM   #10
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Old 11-10-2011, 10:28 PM   #11
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Originally Posted by Cat320 View Post
Some posters may have missed the comment that this is a gas generator. I would do lots of research to see if it's okay to put diesel oil in a gas engine...the majority (that I have seen) say no.
That is what is required by ONAN, Diesel Motor Oil.
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Old 11-10-2011, 11:12 PM   #12
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Onan Gas Generator

While I am new to motorhoming and have diesel genset I do have hundreds of hours on Onan 20 hp - 2 cylinder - 4 cycle air cooled engine. Mostly the CCKB model.

My experience with standard oils was that engine ran rough and had slower throttle response. My use of the Onan's was varying speed for use in Maintenance of Way motorcar on railroads. After several different oils I started using a synthetic Castrol oil for air cooled engines. Changed oil every 100 hours. My engines ran smoother, cleaner and performed better with the Castrol. The Castrol product is available in motorcycle shops.

Realize genset application is different, but engine concept is same. BTW the CCKB engine is cast iron. Folks with the aluminum block version had same results with the Castrol oil.
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Old 11-10-2011, 11:22 PM   #13
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I put Rotella in everything I own, it is one of the best oils on the market. It also save on having a bunch of different oils around. Doesn't matter if I'm changing the oil on my Victory, or my old Toyota pick up, I have a few gallons in the shop for it.

As far as filters go, try and get your filter crossed to a Wix or Napa Gold (re-branded Wix) I also try and keep a running record in a note book or even on the vehicle if you can find a spot to write it down of dates of service and what was done.
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Old 11-11-2011, 12:41 AM   #14
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We have a Power Tech 8.0 KW diesel gen. Has a Kubota 3 cyl engine, I run 15W40 in it, same as the main engine.

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