Onan Smoke

[TJ5208 1,823]

My Onan smokes when I rev my 520 up. I do run seafoam in it but I put a little to much in it this time. My spark plugs are black so could it be the carb needs adjusted? Should I run it out of fuel and try running it off of straight gas?

[ineedanother 1,365]

Hey TJ, I wouldn't be too concerned but any change is worth noting. Seafoam is petroleum based and likely wouldn't cause smoke. Look for other cues to indicate blow-by, but start simple. Make sure the air cleaner isn't causing a rich mixture and keep a good eye on your oil. I think what you're seeing is fuel related and it's actually good that both plugs look the same, but keep an eye (and an ear) on any other warning signs.

[lynnmor 6,762]

You put gasoline in the fuel tank and motor oil in the engine, nothing else is needed.  We can’t help if there are concoctions used.

[TJ5208 1,823]

I do run 10w30 if that help and it does use some oil.

Edited September 5, 2022 by TJ Salyers

[oldlineman 1,450]

If run in the warmer months I would use straight 30 W oil.

[lynnmor 6,762]

I run 30 W oil as well.  Put gasoline in the tank and try 30 W, if it still uses much oil and smokes (all Onans smoke at startup and use a small amount of oil), replace the rings and valve guides. 

[23 Reo 221]

Is 40 W good for summer months? I acquired my first Onan this year.

[TJ5208 1,823]

[23 Reo 221]

Thank you.

[lynnmor 6,762]

The 1997 Owners Manual shows 10-30 & 10-40 up to 80 degrees.  Download that manual for the later information, the engine didn’t change but Onan changed their specifications to reflect the newer grades of oil.