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Topic: Using Full Synthetic Oil For Onan Generator

Posted By: ron.dittmer on 03/28/11 11:50am

Given it is time to change the oil in my Onan 4000 generator, I was thinking of using 30W full synthetic this time. Are there any concerns to using full synthetic oil? My Onan manual makes no mention.

2007 Phoenix Cruiser model 2350, with 2006 Jeep Liberty in-tow

Posted By: JFG on 03/28/11 11:55am

I called onan and they said Synthetics were fine, but not to use them to extend the oil change interval. I use 10W-30.

* This post was edited 03/28/11 12:12pm by JFG *


Posted By: pnichols on 03/28/11 12:21pm

I use Mobil 1 EP in my Onan but do not extend the oil change intervals. I also use this type spark plug in it:

The oil and spark plug, in combination, quiet and smooth the Onan just a bit as well as slightly reduce it's fuel consumption.

(I also use Mobil 1 EP and an E3 spark plug in my portable Honda generator.)

* This post was edited 03/28/11 12:28pm by pnichols *

Phil, 2005 E450 Itasca 324V Spirit

Posted By: bugs53 on 03/28/11 12:28pm

I changed mine to synthetic as soon as I got it home back in 08. Change coach, generator and Jeep every time the coach hits 5,000 miles.
Change the filter too, each time.

Bugs [emoticon]

08 Tiffen Allegro, Wrangler Shahara.2dr std, Us Gear Breaking
Mango 3speed cruisers
Cookie. Springer Spaniel

Posted By: Raymon on 03/28/11 03:18pm

On my previous Onan 4000, I used full synthetic, 5W40 because we used the generator in both very hot weather and cooler weather before it was due for an oil change every 100 hours or once/year.

Posted By: Dakzuki on 03/28/11 05:19pm

ron.dittmer wrote:

Given it is time to change the oil in my Onan 4000 generator, I was thinking of using 30W full synthetic this time. Are there any concerns to using full synthetic oil? My Onan manual makes no mention.

Once broken in, going to syn actually is a good thing on an air cooled engine. Air cooled engines love synthetic oil. They tend to get hotter than water cooled (and have hot spots) so the heat resistance of full synthetic is a bonus.

I will be running mine on full syn once broken in.

Many manufacturers (I am not saying Onan does) recommend breaking in on dino oil before going to full syn to get rings bedded in.

2011 Itasca Navion 24J
2000 Chev Tracker Toad

Posted By: Gene in NE on 03/28/11 10:32pm

Very important consideration - If your small engine (like an Onan generator) does not have an oil filter, be sure to change oil much more often. An automotive engine has a filter to remove the microscopic metal, carbon, or dust particles. An automotive engine running at an RPM that would move the vehicle at 60 miles per hour would travel 3,000 miles in 50 hours. I have changed oil in my automotive engine every 3,000 miles (50 hours) and it has an oil filter.

I would change oil in my small engine mower every 20 hours since it does not have an oil filter.

2002 Trail-Lite Model 211-S w/5.7 Chevy (click View Profile)

Posted By: timwood on 03/29/11 07:06am

I wouldn't use 30w oil though! Single weight oil is waaaaay outdated stuff.


Posted By: ron.dittmer on 03/29/11 08:21am

My 4000 Onan manual says as follows.

32° and higher 30
10° to 100° 15W-40
0° to 80° 10W-30 or 10W-40
?20° to 50° 5W-30

For my camping temps, straight 30 would be most appropriate. It all depends on the type of camping you plan to do for the season.

Posted By: timwood on 03/29/11 02:24pm

As a former aircraft mechanic, I would strongly advise against the straight weight oil.
The first number in the oil is its "winter" number (hence the W, as in 5W-30). With modern oil, that number ONLY applies when the engine, and oil, is cold. Once the oil is at running temp, it acts like a warmed straight weight oil of the second number viscosity anyway.
By running straight weight, you are in effect running molasses for oil until your enging is warm. There are some very very specific reasons you would actually want your oil as thick as molasses, but under most conditions, you don't.
Infact, if your manual is calling for 5w-30, I personally would run 0W-30....and no, it will not void the warranty, because 0w-30 EXCEEDS 5w-30 oil specifications. The lower that first number, the less start up wear to your engine (which is where 99% of your engine wear under normal conditions occurs anyway).

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