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Old 01-10-2018, 01:35 PM   #1
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Onan QD maintenance - Rotella or Onan oil

I decided to do the maintenance this year on my QD 7.5K. I bought the Onan brand oil, air and fuel filters. I found the Onan 15W40 oil online for $15/qt. That seems kinda expensive!
Question: Is Onan oil really that superior or will something else do, like Shell Rotella oil that's sitting in my garage?
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Old 01-10-2018, 01:50 PM   #2
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Depending on your generator usage and outside temperature will dictate the allowable/best oil to use. You can never go wrong using the Onan 15W-40. A very good and less expensive alternative is Chevron Delo 400 15W40. It is specifically designed for diesel applications and runs less than $20.00 a gallon at AutoZone. I realize you only use 3 quarts but it is nice to have a little extra as well. I hope this helps.
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Old 01-10-2018, 04:00 PM   #3
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Me and probably everyone else uses the same oil in the engine and genny. I use rotella 15w40
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Old 01-10-2018, 04:13 PM   #4
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Quote:
Originally Posted by Tha_Rooster View Post
Me and probably everyone else uses the same oil in the engine and genny. I use rotella 15w40
+1.
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Old 01-10-2018, 04:16 PM   #5
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Quote:
Originally Posted by Tha_Rooster View Post
Me and probably everyone else uses the same oil in the engine and genny. I use rotella 15w40
Agree.
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Old 01-10-2018, 04:20 PM   #6
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Wow--Onan 15w-40 is $5-6 at my local Cummins.....otherwise, use in the Onan what you use in the diesel RV engine...makes carrying extra oil much simpler....same applies for the Onan coolant---its not a wet-sleeve engine so whatever you use in the RV engine is fine there too...Don't even want to ask where/what you paid for the filters?? Curious, how often do you change oil/ filters in yr Onan?
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Old 01-10-2018, 04:35 PM   #7
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Thanks for all the input!
Turns out what I thought was Rotella in my garage was actually Delo, that I use for my truck...
No local Cummins, so online abt $70 for oil/air/fuel combo. I'll have to compare when I get to a Cummins shop...
2nd year of ownership of a 08 coach - initial svc done by Cummins. Put abt 400 hrs on the genset last season.
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Old 01-10-2018, 05:22 PM   #8
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Originally Posted by DFitz View Post
Thanks for all the input!
Turns out what I thought was Rotella in my garage was actually Delo, that I use for my truck...
No local Cummins, so online abt $70 for oil/air/fuel combo. I'll have to compare when I get to a Cummins shop...
2nd year of ownership of a 08 coach - initial svc done by Cummins. Put abt 400 hrs on the genset last season.


I purchase all my filters at rvchassisparts.com
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Old 01-11-2018, 10:43 AM   #9
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Quote:
Originally Posted by Tha_Rooster View Post
Me and probably everyone else uses the same oil in the engine and genny. I use rotella 15w40
Yup!
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Old 01-17-2018, 11:57 AM   #10
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FWIW I just left the Freightliner factory service center in Gaffney SC.

I had my engine and genny oil changed.

The ONLY oil they carry is Rotella 15W40 for both applications.
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Old 01-17-2018, 12:04 PM   #11
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My Onan 12.5 has a Kubota engine. I use the same oil in it as the ISX. The coolant is different as I haven't changed to an OAT coolant in it like I have in the ISX.
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Old 01-17-2018, 12:21 PM   #12
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Quote:
Originally Posted by Mr_D View Post
My Onan 12.5 has a Kubota engine. I use the same oil in it as the ISX. The coolant is different as I haven't changed to an OAT coolant in it like I have in the ISX.
Yup, 15/40 Delo or Mobile equivalent for engine & Kabota gennie.
Went with the NAPA Yellow/Orange OAT for all coolants, including the boiler on our AquaHot.
(NOTE!!!!! Our AquaHot is an older model (exe-100-02s) that uses regular antifreeze vs "boiler fluid" used in the newer models)
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Old 01-17-2018, 05:09 PM   #13
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Just a FYI, if you want to run synthetic, 5W-40 is the synthetic diesel oil. 15W-40 are conventional oil. I agree with all the previous replies, any diesel rated oil is fine for your generator.

I run synthetic 5W-40 in my generator, but with 11 gallons required in my ISX engine, I use the conventional there.
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Old 01-20-2018, 11:03 PM   #14
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Quote:
Originally Posted by 38Chevy454 View Post
Just a FYI, if you want to run synthetic, 5W-40 is the synthetic diesel oil. 15W-40 are conventional oil. I agree with all the previous replies, any diesel rated oil is fine for your generator.

I run synthetic 5W-40 in my generator, but with 11 gallons required in my ISX engine, I use the conventional there.
Ditto... My mechanic recommended the synthetic 5W-40 for my generator. Runs a little quieter too... (IMHO)...
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