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Old 11-25-2020, 05:26 AM   #1
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Onan 4000 Oil Change

I need to change oil in Onan 4000 generator and research indicates manufacturer's (Cummins) replacement is very expensive but that some people have used SAE 30. Looking for free advice here -- what do y'all think? $25 and up for Cummins or much less for the SAE 30? Who has done what? Results? Don't want to be penny wise and pound foolish but as we all learn quickly with RVs, they get you coming and going on specialty items. Thanks in advance.
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Old 11-25-2020, 05:37 AM   #2
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Since Cummins is not an oil manufacturer, I use the appropriate weight oil. Gas and LP seem to use 10W30 and diesel 15W40. I have been doing my own oil changes since my first car 40 years ago and always use whatever synthetic that is on sale. Haven't lost an engine yet.
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Old 11-25-2020, 08:03 AM   #3
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I have always just used moble 1 with no problems
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Old 11-25-2020, 10:32 AM   #4
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I use straight 30w in my Onan 4000 per mfg's suggestion for temps above freezing, since we don't intend to camp in cold weather anyway. I think the straight weight oil might give a little better protection in hot weather. My understanding is that multi-weight oils main advantage is for easier starting in cold weather.

BTW, I have been changing my own oil since the 1960's (cars, trucks, tractors, motorcycles, lawn mowers) and have never once used full synthetic oil in anything. I have never lost an engine either.
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Old 11-25-2020, 02:33 PM   #5
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Quote:
Originally Posted by Homer3 View Post
I need to change oil in Onan 4000 generator and research indicates manufacturer's (Cummins) replacement is very expensive but that some people have used SAE 30. Looking for free advice here -- what do y'all think? $25 and up for Cummins or much less for the SAE 30? Who has done what? Results? Don't want to be penny wise and pound foolish but as we all learn quickly with RVs, they get you coming and going on specialty items. Thanks in advance.
I recently changed it after 100hrs
I used 30wt as I live and travel in a mild climate
Here’s a link on how to change yourself.

https://YouTube-change Onan 4000 oil
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Old 11-25-2020, 03:17 PM   #6
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Any advice for those of us with diesel generators?
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Old 11-26-2020, 03:52 PM   #7
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Bob- Manual for Diesel Genny. Recommends 15w40 for 10 deg to 100+ and 10w30 for 0 to 100+ Chart on page 2-1 Cummins Onan does not recommend synthetic oil as not cost effective....
http://www.skilledcrafting.com/onanf...0(06-2010).pdf

For the gas generator.. https://www.norwall.com/product_pdfs..._om_2_2018.pdf
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Old 11-26-2020, 03:54 PM   #8
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Just as we have determined what oil to use, Cummins Onan changes the numbers.... https://www.cummins.com/generators/m...-rv/onamax-oil

Kinda gets to- use what you have.. I have a Snapper riding mower, Snapper book calls for 30 wt oil. Briggs engine manual shows 15w50.. and then there is the Sprinter 4 page brand specific approval oil list (BEVO)
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Old 11-26-2020, 04:08 PM   #9
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Thanks!
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Old 11-26-2020, 09:08 PM   #10
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I didn't think the Cummins oil was that expensive. Like 6 a quart.
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Old 11-29-2020, 04:42 PM   #11
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Quote:
Originally Posted by Campnjoe View Post
I didn't think the Cummins oil was that expensive. Like 6 a quart.
But that's a 1.6 quart oil change every 150 operating hours..
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Old 11-29-2020, 04:57 PM   #12
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Oil is cheap; when you compare it to generator repairs and replacements.
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Old 11-29-2020, 05:03 PM   #13
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Bob

The oil is easy to change out on the generator. I do have the Cummins oil here at the house but found that our last trip to Yellowstone, I needed to add oil but didn't bring it with me. I found some oil at a Sinclair gas station inside Yellowstone that met the requirements(diesel generator) so I added the oil. I now keep some of the oil onboard at all times. Lesson learned.

Paul
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Old 11-29-2020, 05:50 PM   #14
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I don't tend to carry spare fluids; I may have to reconsider this decision.
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Old 11-29-2020, 05:58 PM   #15
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I always carry extra oil for the generator and for motor. Probably a habit from boating or driving old cars there always seems to be some burn off.
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Old 11-29-2020, 08:09 PM   #16
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The mysticism of oil is a holdover from postww2 days and that's a holdover from when oil was not regulated. Whale oil was a preference back then.

Oils are certified now.
I buy bulk and everything gets the same oil.
It hasn't been an issue since the mid sixties and a bit before.
Even the old
Double eagle
was certified back then.

It was a worry for your grandparents due to parrafin and lead and gasoline blowby in cylinders and such.

If they didn't make wild-ass claims and add secret sauce they wouldn't need a marketing department.
Job security requires secret sauce.
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Old 11-29-2020, 08:37 PM   #17
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I'm not real fussy about oil.
The riding mower, string trimmer and leaf blower all get the same 30 weight stuff.
The Escape and Smart get whatever the dealer puts in them.
The RV will also get what the dealer uses.
I figure that they don't like warranty claims; they'll choose the right stuff.
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Old 12-02-2020, 07:28 PM   #18
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Quote:
Originally Posted by Homer3 View Post
I need to change oil in Onan 4000 generator and research indicates manufacturer's (Cummins) replacement is very expensive but that some people have used SAE 30. Looking for free advice here -- what do y'all think? $25 and up for Cummins or much less for the SAE 30? Who has done what? Results? Don't want to be penny wise and pound foolish but as we all learn quickly with RVs, they get you coming and going on specialty items. Thanks in advance.
I just did mine last week SAE 10-30 Pennzoil easy to do
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Old 12-02-2020, 07:59 PM   #19
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Me too!

Synthetics do lower friction and resistance, and increase mileage, but, that's not an issue with generators. Non-synthetics are actually better for for the engine seals, and are a better choice for maintaining an engine. I've always preferred straight weight oils as they don't break down as quickly as multi-viscosity choices, at least for utility and farm equipment.
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Old 12-02-2020, 08:11 PM   #20
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I have been using Shell Rotella T6 Full Synthetic Diesel Motor Oil SAE 15W-40 in my Onan QG4000 now for over a year and no issues. I live in WA state, so temps range from 0F-110F.
I dont carry extra oil as I am afraid of a spill in my RV but i do check the level prior to long trips in the generator as well as the RV engine.
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