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Old 08-11-2021, 08:18 PM   #1
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Synthetic oil in Onan

Hi all,

Has anybody used synthetic oil in their Onan generator. Mine is due for an oil change and I am thinking synthetic.

Thanks

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Old 08-11-2021, 08:33 PM   #2
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Exclamation

Cummins does not recommend the use of Synthetic oil in Onan RV generators as there are no long-term benefits for the additional cost. The best oil you can use for your Onan 4000 generator would be a SAE 30W viscosity oil. Use a 10W40 oil viscosity when changing the oil in your 5500 generator.
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Old 08-11-2021, 08:40 PM   #3
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Let me paraphrase a respected mechanic I know who runs a big Cummins marine diesel shop in California: "I have never seen a properly maintained diesel engine harmed by regular, petroleum based lube oil."

Yes some synthetics have better lubricity properties than petroleum oils. And they last longer due to their chemistry resisting breakdown due to heat and time.

But they work well enough with petroleum based oil if you stick to Onan's oil change interval. If you want to extend it to 300 hours, then use synthetic oil.

David
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Old 08-11-2021, 09:11 PM   #4
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Quote:
Originally Posted by Popfla View Post
Cummins does not recommend the use of Synthetic oil in Onan RV generators as there are no long-term benefits for the additional cost. The best oil you can use for your Onan 4000 generator would be a SAE 30W viscosity oil. Use a 10W40 oil viscosity when changing the oil in your 5500 generator.


Onan recommends 15W40 conventional oil for their 4000KY and thatís what I use. I was in Texas during the unexpected deep freeze last February and had to start mine in the wee hours of a night during a sleet storm. Iím glad I didnít have 30W in it!
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Old 08-11-2021, 09:34 PM   #5
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Originally Posted by Pete'sMH View Post
Onan recommends 15W40 conventional oil for their 4000KY and thatís what I use. I was in Texas during the unexpected deep freeze last February and had to start mine in the wee hours of a night during a sleet storm. Iím glad I didnít have 30W in it!
What I posted was from Onan's user manual for the 4000 model.
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Old 08-11-2021, 10:50 PM   #6
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Thanks for all your input.
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Old 08-11-2021, 11:12 PM   #7
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Originally Posted by Popfla View Post
What I posted was from Onan's user manual for the 4000 model.


No more so than mine wasÖ.
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Old 08-11-2021, 11:54 PM   #8
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Quote:
Originally Posted by Popfla View Post
Cummins does not recommend the use of Synthetic oil in Onan RV generators as there are no long-term benefits for the additional cost. The best oil you can use for your Onan 4000 generator would be a SAE 30W viscosity oil. Use a 10W40 oil viscosity when changing the oil in your 5500 generator.
Same here


Onan 4000 generator would be a SAE 30W
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Old 08-11-2021, 11:57 PM   #9
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Hey after how many hours do folks change the Onan 4000 gas oil?
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Old 08-12-2021, 12:19 AM   #10
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Here's a good read......

https://newsroom.aaa.com/2017/06/aaa...-oil-changes/#

I use Synthetic or Synthetic Blends depending on the application. There are plenty of studies that show for a few extra bucks the benefits far outweigh the difference in price.

If you use conventional oil and follow the recommended maintenance schedule, you won't have any problems.

But when you are using an engine for "sever duty" applications, which I include as most motorhomes.... and even generators when temps are 90 degrees or higher.... the exra money for synthetic is worth it.

I can do a 12 quart oil & filter change for my SV34 for $80. The Ford sealer chargers $110 for conventional. Why wouldn't I use Synthetic for a 10-ton motorhome when I can do it for less? There's no downside.

I just changed the oil in my QD6000 last weekend and used Shell T5 15W-40 Synthetic Blend that met the Onan specs.
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Old 08-18-2021, 09:29 PM   #11
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I use synthetic 5w30 on both the 10kwQD and the L9 450 hp Cummins main motor. I change both myself on an annual basis.
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Old 08-18-2021, 10:54 PM   #12
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I use synthetic oils on all my engines

I use synthetic oils on all my engines: Car, RV, Generator, Mower, etc.

it's more expensive, but I'm not worried if I used it past it's normal oil change, or if the temperature will be hot or cold.

Less breakdown from heat means less residual stuck inside the engine.

I used to rebuilt car engines back in my youth and saw the difference first hand.

Mobil 1 is my first choice, but I will use other brands if Mobil 1 is not available for whatever reason.
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Old 08-18-2021, 10:55 PM   #13
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At the first oil change on my 4000, I used Mobil 1 10-40. In KS we can get temps over 100 and under 0 degrees.
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Old 08-19-2021, 12:11 AM   #14
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Since temps in south AL easily hit close to 100 in the summer and below 20 in the winter, 15W-40 for me.
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Old 08-19-2021, 12:21 AM   #15
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I have 540 hours on Onan 4000 in Vegas. It get oil change annualy with 15w-40 conventional per manual. Is 6 years old. No issues or oil use so far.

All my other air cooled equipment use the same oil. The 3500 champion on race car trailer I bought week after RV probably has over 5000 hrs now. I have had to replace starter twice due to broken spring but it still does not use oil.

Key to generator life is oil changes and keep linkages lubed.
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Old 08-19-2021, 03:36 AM   #16
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Oil change interval on the 4000 is 20 hrs/150/300/450/etc @ 150 hours. according to the 4000 manual.
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Old 08-19-2021, 04:58 AM   #17
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Can anybody cite a real life case or experience where whatever oil was used properly for routine maintenance every year or every 150 hours, there was a problem?

I use Chevron Delo 400 15w 40 https://www.walmart.com/ip/Chevron-D...E&gclsrc=aw.ds; it has a answer for every thing the oil czars wishes to throw out as important. I use it in the F-53 and Onan 5500.

With that said, if I wanted to be technically prudent, I would change oil twice a year regardless of hours. October with the Chevron Delo 400 and 6 months later in March with my favorite 30w oil of the day (This assumes you live in the South where it gets really hot; otherwise stick with the 15w 40
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Old 08-19-2021, 10:10 AM   #18
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I use synthetic Diesel oil and change at 200 hours or close
15-40 wt
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Old 08-19-2021, 11:48 AM   #19
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Have never seen an oil quality related faiure in anything including drag bikes, race motors etc. Choice of viscosity and change interval dependent on application. The RV onan get annual change as it never sees 150 hours in a year. The champion is every 90 days when we race a lot. The RV has been sitting so likely will change in Nov because we have been on any big trips. With all the rain, we have only raced twice this summer.

Time vs hours/miles is used when oil sits inactive. In Florida swamp if you leave something with open vented crankcase, rust starts. I pulled sons old racecar out and put engine in my car for 1 year. Then pulled apart and replaced rings/bearings/gaskets. They only real downside I found was rust stains on crank journals and cylinder walls. I had periodically run my oil primer to keep engine free. Newer stuff has better control of crankcase venting but I trust new oil more than old.
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Old 08-19-2021, 12:17 PM   #20
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Keep in mind we are talking about RV generators. So when deciding on oil weight, remember it doesn't sit in one location and one weather environment. By going with the weight for the greatest temperature range you possibly could experience, you are getting the best protection and performance.
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