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Old 12-09-2022, 07:41 PM   #1
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onan 4000 oil

have been using Onan 15w40 oil since new. getting a little pricy on amazon. what does anyone use as an alternative with same specs(SJCH-4) or (SGCH-4).
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Old 12-09-2022, 09:09 PM   #2
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My old 4000's manual states straight 30 weight with an API of SJ as being the preferred viscosity in temperatures above 32įF. I've used the Supertech brand for the last 19 years. No problems to report!

Most all today's oils have classifications greater than SJ so I really don't think it matters what brand, as long as you go with the right viscosity for the ambient temperatures you're going to be running in.
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Old 12-09-2022, 09:48 PM   #3
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Sorry OP, but I did a search on the 'net, "onan 4000 oil" and got this website

I thought it funny enough to share...
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Old 12-09-2022, 11:22 PM   #4
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THE LATER OILS 15W40 diesel CK4 oils w/ SN (gas spark engines) is backwards compatible label will read CK4/SN - = DIESEL AND GAS; PAY ATTENTION, GET the SN on the label, many diesel oils are NOT also SN Rated. i USE WM, or Costco when in stock.
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Old 12-10-2022, 05:19 AM   #5
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I've always used the SuperTech. ONAN changed oil specs for the ONAN 4000 (gas generator) from 30w oil to 10w-30 oil. Make sure it is SN or newer SP rating. You can still use 30w oil.
This is from the latest Cummins ONAN handbook:
10W-30: preferred oil for gasoline/LP generators

15W-40: preferred oil for diesel generators

NOTE: All generators are shipped from the factory with 15W-40 oil, 10W-30 for gas.
You can get the Handbook here (oil chart is on pg 33):

https://www.cummins.com/generators/rv-generators
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Old 12-10-2022, 02:04 PM   #6
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Quote:
Originally Posted by Bill 3rd View Post
I've always used the SuperTech. ONAN changed oil specs for the ONAN 4000 (gas generator) from 30w oil to 10w-30 oil. Make sure it is SN or newer SP rating. You can still use 30w oil.
This is from the latest Cummins ONAN handbook:
10W-30: preferred oil for gasoline/LP generators

15W-40: preferred oil for diesel generators

NOTE: All generators are shipped from the factory with 15W-40 oil, 10W-30 for gas.
You can get the Handbook here (oil chart is on pg 33):

https://www.cummins.com/generators/rv-generators
Imo, this handbook makes it a bit confusing. Here's a quote from it.

Quote:
. This handbook is a general supplement to the more
specific information contained in the operator manual that comes
with every new Cummins generator.
This statement seems to say that it's be better to go by what my specific manual says. And of course, my manual shows straight 30 to be preferred. I was hoping there might be some wording to the effect that Onan updated their recommendations, but this doesn't seem to be the case.

In the end, I doubt it matters much for most people. I can't remember the last time I ran the genset in temperatures below freezing so I'll keep using the 30W.
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Old 12-16-2022, 07:07 PM   #7
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I use 10w-30 synthetic in ours on the west coast. Rarely have freezing temps and a few weeks every summer over 100 degrees. I believe your location needs to considered as well and where you run it most often. The newer oils are much better quality than a few decades ago. If you follow the Onan specs no need to spend more for brands. Check out Walmart Tech brands as an example.
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Old 12-17-2022, 10:17 PM   #8
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Use Valvoline 10w-30 VR-1 Racing conventional (silver bottle)
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Old 12-18-2022, 10:00 PM   #9
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I use the cheapest straight 30 weight I can find and change it on schedule. Never a issue.
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Old 12-19-2022, 02:40 PM   #10
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Amen brother. Kinda makes one think of the last time you heard of an Onan generator (or any gas engine for that matter) failure due to wrong oil or lack of lubricarion. Regular oil changes are way more important than brand or specs IMHO. I'm certain others disagree but 7+decades are my observations and experiences. Probably some small differences in wear patterns and such but we tend to follow the experts' recommendations or use common sense.
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Old 12-19-2022, 09:24 PM   #11
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Originally Posted by Mudfrog View Post
In the end, I doubt it matters much for most people. I can't remember the last time I ran the genset in temperatures below freezing so I'll keep using the 30W.
Oooops! Supposed to get into the teens this weekend, hope I don't have to use the genset.
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