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Old 08-03-2019, 06:31 PM   #1
" Winnie Nutt "
Join Date: Jul 2019
Location: North Carolina
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Question Onan Generator Oil

Is synthetic oil or regular 10W40 motor recommended for the Onan QD 3200 diesel generator . Time to change my oil but can't find which type is recommended . Does it matter ?
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Old 08-03-2019, 09:34 PM   #2
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I use Shell Rotella 15W-40. Personally don't think it matters, just get the correct weight. I always have the Rotella for the tractors etc. and I used it in our Pusher as well. Synthetic doesn't stay in long enough to reap the benefits IMHO. If you run the generator a lot (we do) you are adding oil every other day to keep it topped up.
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Old 08-04-2019, 09:32 AM   #3
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Not all are the same so I would want to check the recommendations for that specific unit. Gensets are kind of a weird item on maintenance as so much varies with how we each use them and how we each deal with that. I doubt synthetic would be much value but the correct weight and type is a definite plus as it can vary depending on where and how you use it. Starting a gen in cold weather with too thick oil can leave it running without good lube so that things wear quicker but running in hot can be the same if the oil is not thick enough.
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Old 08-11-2019, 06:16 PM   #4
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Oils for diesels are made with different additives

Diesel engine oils are designed for the diesel combustion byproducts that leach into the oil. The oil then neutralizes this and or keeps it in suspension etc etc. So if you use an oil designed for gasoline engine in your diesel you would be doing it a disservice. BTW on my lawnmower (gasser) i have always used diesel engine designed oil and my gas motor loves it, never a problem the logic there is those engines burn fuel so badly that a lot of combustion byproducts get into the oil and so the diesel design process works best for em. They say an hours use of a push mower powered by gasoline is equivalent of emissions caused by a car driving between 100 to 200 miles depending on size and make.
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Old 08-11-2019, 06:30 PM   #5
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I use "dino" oil in my generator -- same as my diesel Cummins engine. I have heard before on this forum that some generators do not like the synthetic oil and will shut down for low oil even though the oil level is at the correct level. Since I change out my genny oil each year as recommended (change it when I change the "big" engine oil and filters, I don't feel that synthetic is worth the extra cost anyway.
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Old 08-11-2019, 10:20 PM   #6
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Just my thoughts,

Can a person go wrong using Cummins Onan oil and parts?. That said, a local Cummins Onan Dealer has told me they have no issues with using Shell Rotella or comparable oil in a Generator if their Onan oil is unavailable. I'm sure many folks use different oil.

Maybe this link to Cummins Onan online store will help with information in the future. If you enter your Generator model information you can get Mfg parts info. Or just give Cummins a phone call. They should be able to give some additional information for your generator.

A local Cummins Onan dealer sold me ONAMAX 15W40 oil at less than 1/2 the price it was listed for on Amazon and then gave another 10% off with a military ID. About $5.40 Qt.
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Old 08-12-2019, 03:57 AM   #7
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The OP has an Onan/Cummins QD3200. If you go to the parts store link provided you can buy a manual and their oil. Can't even find the air filter (Meltons has it).

Going to the Cummins Onan shop does not mean you will get the right part either. Last Pusher we had with a much larger diesel generator they insisted on giving me an oil filter that would not fit. Finally asked for the generator tech to help me (really got the counter guy angry). The generator tech looked at my engine info, walked right to the shelf and came back with the correct oil filter - made by Kubota, labelled Kubota. After that I ordered the Kubota part since the engine in the genny was Kubota and it was half the Cummins Onan price.

The requirements for modern diesel engines do not apply to the little diesel in the QD3200 made by Hatz. It has no DEF, no EGR etc. It probably will run on kerosene if you feed it that.

It is smart to use an oil like Shell Rotella 15W-40 since it does meet many new diesel requirements. I would never use the MB oil they require in the engine for the little Hatz engine however. So far my little QD3200 is humming along fine just over 200 hours at 18 months of use. It varies by manufacturer. My diesel ZTR Kubota lawnmower specifies synthetic oil, specifically a Kubota oil. It lives on Mobil 1 synthetic which meets the spec because Mobil 1 is still half price of picking the junk up at Kubota labelled Kubota. About 1200 hours on that little diesel and it is still happy. It is the exact engine that powered the last generator in our DP which I always fed - love it - Shell Rotella 15W-40.

Every manufacturer seems to be marketing their own oils now. MB with the new Sprinters can drive you nuts - cheapest oil to find around here is the MB oil so I buy it from the MB car parts (don't service Sprinters but stock the oil). Yes, it prices out less than ordering the impossible to find Mobil 1 which is not sitting on any shelf near our location. Even Subaru wants you to use Subaru oil - nope, Mobil 1 goes in both my new Suby engines. The law says if you use the right spec oil you can buy it anywhere with any label on it as long as it is certified (whatever that means) to spec.

There is some discussion that synthetic oils might be a better choice in diesel engines in case of engine run away - dino oil burns a whole lot easier.
Bill and Brenda + Mobius Big Dog
2018V24D, '13 Tiffin BR32, Tiffin 34TGA, '11 Aspect 30, 06View23H, '00 HHiker II 5W
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Old 08-12-2019, 06:13 AM   #8
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The way I see it you must stick to manufacturers recommendations or adhere to the viscosity of the oil they use..Different brands does not seem to matter ..just dont put 0-20 lightweight in it , that stuff is like water.
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Old 08-12-2019, 07:01 AM   #9
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Full synthetic 15w 40 oil is only oil I run in all diesel engines.
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Old 08-12-2019, 08:04 PM   #10
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Its been my understanding that the ONAMAX 15-40 is really Valvoline Blue Diesel Oil so any Diesel Oil that meets that API Service Rating will do meaning any 15-40 Diesel Oil will be fine be it Rotella, Delvac, Delo, etc, etc. Synthetic Diesel Oils may give you a slight edge in extremely hot conditions which is what Onan techs recommend.

To put things into perspective running a generator for an hour could be likened loosely to the equivalent of riding a motorcycle down the highway for an hour at 60 mph so every 50 hours of generator use would be about the same as riding 3,000 miles. Something to keep in mind when running the generator while driving on long trips since your generator if not using synthetic oil may need oil changes twice as often as the vehicles engine.
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