robertmoretto
Hi, I'm new to this forum. I have a 20 yr old water cooled 20kw Generac with 450 hrs on it. Engine crank case is clean as a whistle as is oil when I drain it.With all the new products out there I was wondering what is the best oil to use for these standby generators that get little to no use? And how often should it be changed?
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Cobranut
I prefer a name brand synthetic oil in pretty much everything  I run.
Just be sure it's appropriate spec and weight for the temperature range it'll be operating in.
I like Mobil 1 in my gas engines, and I use Shell Rotella T6 5w40 in my diesels, including my generator.
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78buckshot
Most of the liquid cooled of that age spec a 15W-40, Valvoline makes a 15W-40 specifically for natural gas engines, it's the only oil that Cummins/Onan recommends for some of their machines.
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Cobranut

Buckshot:  I wasn't aware of that oil.  I'd trust Valvoline as well, they've always been known as a very good oil brand.

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78buckshot
Cobranut, I am able to order it through NAPA but it's not an item they keep on the shelf. I maintain a couple of Cummins 60kw with Ford V-10 engines, the Valvoline is what they spec.
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Charles G
oil use is a long debated item , is the motor gas or diesel ?  one can not use the oil for one in the other,  best advise is read the owners manual and take note of the grade ratings the engine  maker advises to use,
almost all break it down to  the  grading's,  SF or usage , SAE weights. this posting may help many understand what techs have to understand 
http://www.pqiamerica.com/apiserviceclass.htm
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robertmoretto
 Charles G/ Generator is over 20 yrs oil manual way outdated. After all your responses I did some research and found this oil to be one of the best for LPG & natural gas engines mobil delvac cng/lng 15w40. Very hard to find someone who stocks it, had to special order. Thank you all for your input. 
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