Onan RV 4000 generator oil change

[jimbo21793]

Just talked to the onan Cummings distributor in Baltimore. He advised me to use
15/40 weight oil (diesel) in my generator. Anyone else hear this ?
I was using w30 weight regular ole oil.

[Campnjoe]

They sell their own onan branded oil that the manual calls for. Its actually pretty reasonably priced.

[Pete'sMH]

The owners manual recommends the 15w40 but is ok with 30w if it’s going to be hot. But why wouldn’t you use the multi weight? I went to south Texas last month expecting 70 degrees but I found myself doing a cold start at 14 degrees at 4:00 in the morning. Fired right up and ran for MANY hours over the next several days. It only holds 1.6 quarts so I generally use the Onan branded oil - which is silly expensive at about $6/qt. But really, if you change it once a year $9 isn’t gonna kill you.

[jimbo21793]

Originally Posted by Pete'sMH

The owners manual recommends the 15w40 but is ok with 30w if it’s going to be hot. But why wouldn’t you use the multi weight? I went to south Texas last month expecting 70 degrees but I found myself doing a cold start at 14 degrees at 4:00 in the morning. Fired right up and ran for MANY hours over the next several days. It only holds 1.6 quarts so I generally use the Onan branded oil - which is silly expensive at about $6/qt. But really, if you change it once a year $9 isn’t gonna kill you.

Is it ok to use the synthetic 15/40?

[Pete'sMH]

Originally Posted by jimbo21793

Is it ok to use the synthetic 15/40?

I personally believe synthetic pretty much always is “better”, but I think I read on another thread that Onan specifically recommends against it. It’s an understressed engine operating at a fixed rpm so it probably is happy on whatever it gets.

[Elite Washington]

I think I would always use multi weight oil. Living in the northwest is the reason. But I have been in Montana and seen snow in July.

[taylorbob1]

I use 30wt in SanDiego
Boring weather here