Onan 5500 Generator ... what oil??

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winnie32v

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Mar 17, 2012
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I have an Onan 5500W Generator and I need to change the oil.
Just bought this unit a few months ago and this job is on the list of maintenance things to do.
So, what type and viscosity is recommended?
I was even thinking of a synthetic oil, but wasn't sure if that was OK if the generator has about 280 hrs on it.

Thanks for the advice.
 
That generator is WAY under-utilized/maintained!  It needs to be run under load apx 1hr per month, oil changed every 150 hrs OR 12mo whichever comes first. I suspect you could download the manual fron Cummins/Onan ...without that I would use a good 10/40w oil. I would not waste my $$ on synthetic.
 
I use Mobil1 20-50 Synthetic Oil.  We have nearly 500 hours on our 2006 model Onan 5500.

Onan recommends 15-40 oil.
 
Use a diesel specific 15/40 oil, there are lots of good choices, Delo 400, Shell Rotella, Mobil Delvac are all good. If you are going to use the generator in a very cold climate, consider Rotella 5/40 synthetic for easier cold starts. Walmart is a good choice for value on these oils.
 
nuffsaid said:
Use a diesel specific 15/40 oil, there are lots of good choices, Delo 400, Shell Rotella, Mobil Delvac are all good. If you are going to use the generator in a very cold climate, consider Rotella 5/40 synthetic for easier cold starts. Walmart is a good choice for value on these oils.
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This is a gas generator.  As stated above, I went to the Onan website and looks like they recommend a 15w-40 oil for the most versatile conditions. (I'm from Pa. )
So, I'll be looking into this.
next, is to remove oil filter and see what kind that is and replace it.
I have running this generator for 2 hrs each month at about 1/2 load (air conditioner) and it runs well. starts on the second try.

Any more suggestions will be appreciated.
Thanks for your time.
Paul
 
Note that the last of the two quarts takes a long time to fill. I fill the filter before I install it and that helps reduce the time a little. When it gets super slow I also screw the dip stick back in and turn the engine over some. That seems to drop the level enough to speed up adding the last of it.

I used 30 weight for years since I don't run it in cold weather but have switched to Mobil One 10W 30.
A number of folks posted that Onan customer service said that was a good choice.
 
For a gas generator, most people use plain SAE 30 because they don't ever run in cold weather (below freezing) and SAE 30 is optimum for warmer weather (per the Onan Handbook). 10W30 or 15W40 is optimum if you want to cover sub-freezing temperature operation as well. The API service level should be SJ, SL, or SM.
 
Go with the weight that Onan recommends and stay with a name brand oil. As afchap said, I wouldn't waste my money on synthetic oils, (snake oil in my opinion). 

I would also recommend that you add some Sea Foam to the fuel supply in the appropriate amount.  The biggest issue you are going to run into nowadays is the fact that pretty much all fuels (gasoline) have at least 10% Ethanol.  Ethanol DOES NOT age gracefully!!  Sea Foam or Stabil will give you a fighting chance of not having to replace your carb.
 
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