Note: Our typical camping climate range runs from 10F to 115F (if we go to Redding, CA in the summer... otherwise up to about 105 in Southern Oregon.)Clearly Onan/Cummins have updated their recommendations for the old BFA. Whereas they once recommended 30W only, they now have a chart with several recommendations for different temp ranges with a nod to 15W-40 (I'm currently using) for the widest ranges. But no mention of 20W-50. And my searches (though they do show some guys running 20W-50 with no problems and some with) turn up little mention either. Why?Now I know that 20W-50 is not a perfect 20 nor a perfect 50 for their prospective temp ratings, but it still seems that if 30W worked back in the day, that 20W at cold temps is better than 30W and 50W on a hot day is better than 30W.The only thing that I can reckon is that a good 30W is... pretty much always a 30W and doesn't break down to anything less. But that shouldn't be an issue to anyone who changes their multi-weight oil often enough.Now theoretically, other than the potential for thermal breakdown in time or overheating, a 10W-30 should act the same as a straight 30 at 212F. So why the difference in the chart below?The reason I even ask is I run 20W-50 in the 454 (another conversation) and I wouldn't mind just keeping one spare oil type aboard.The only other thing I can figure is that Onan would prefer the lower resistance for the little 2 banger to better lubrication. When I get a chance... I'll ask 'em.Your thoughts?.

Your logic sounds good to me.However, if you call Onan, IMO the chances of getting an actual Onan engineer to commit to a debate on the pros and cons of using 30w vs. 20w-50 is highly unlikely. More than likely you'll never get farther than the typical technical support rep who doesn't have the necessary engineering background to authorize a deviation from the guidelines established in the owner's manual.If your Onan is under warranty and you're operating in ambient temps above 100 degrees, 30w is the only way to go---if you want to keep your warranty intact. If your Onan is not under warranty, and you're willing to take the risk, then give 20w-50 a try. If it doesn't sieze or blow-up, get an oil analysis and go from there.

There was a similar post just a few days ago about generators and Sprinter oil. It occurred to me then and does now, also, how much oil of a different weight is needed for the generator? My guess is a quart or less.

My thought for the higher side of the temperatures you mention, the 20W50 is fine. At 10 degrees it may be a little heavy. If it cranks over and starts OK you're good.

Have you tried the 20W-50 in your onan yet? I tried a multi-weight oil in my Emerald 3 6.5 once and found that it burned through way too much oil. I do not recall which multi-weight oil I tried, however, and I did try it during the summer.Miles

Son of Norway wrote:Have you tried the 20W-50 in your onan yet? I tried a multi-weight oil in my Emerald 3 6.5 once and found that it burned through way too much oil. I do not recall which multi-weight oil I tried, however, and I did try it during the summer.MilesNo.Been using 15W-40 for the last several years. I can say that she does burn through a bit of oil, but I can't recall whether or not she did with just straight 30.Overall she runs well. But when it's hot, if I shudder' down for a bit, she won't exactly clamor at the thought of starting up again. Though she will fire up again eventually. But that was the case with straight 30 too.It's important to keep in mind that she'll run the overhead A/C for hours with the mercury up and over a hundred and only stop when I hit the kill switch.

Onan BFA Oil - Why not 20W-50? | Good Sam Community

RLS7201
Explorer II
Jul 23, 2016
Every thing you ever wanted to know about oil is at Bob is the oil guy.
I linked to his viscosity article but there a weeks worth of reading on his site.

Richard
KendallP
Explorer
Jul 23, 2016
Son of Norway wrote:
Have you tried the 20W-50 in your onan yet? I tried a multi-weight oil in my Emerald 3 6.5 once and found that it burned through way too much oil. I do not recall which multi-weight oil I tried, however, and I did try it during the summer.

Miles

No.

Been using 15W-40 for the last several years. I can say that she does burn through a bit of oil, but I can't recall whether or not she did with just straight 30.

Overall she runs well. But when it's hot, if I shudder' down for a bit, she won't exactly clamor at the thought of starting up again. Though she will fire up again eventually. But that was the case with straight 30 too.

It's important to keep in mind that she'll run the overhead A/C for hours with the mercury up and over a hundred and only stop when I hit the kill switch.
Son_of_Norway
Explorer
Jul 23, 2016
Have you tried the 20W-50 in your onan yet? I tried a multi-weight oil in my Emerald 3 6.5 once and found that it burned through way too much oil. I do not recall which multi-weight oil I tried, however, and I did try it during the summer.

Miles
tpi
Explorer
Jul 23, 2016
My thought for the higher side of the temperatures you mention,
the 20W50 is fine. At 10 degrees it may be a little heavy. If it cranks over and starts OK you're good.
westend
Explorer
Jul 23, 2016
There was a similar post just a few days ago about generators and Sprinter oil. It occurred to me then and does now, also, how much oil of a different weight is needed for the generator? My guess is a quart or less.
otrfun
Explorer II
Jul 23, 2016
Your logic sounds good to me.

However, if you call Onan, IMO the chances of getting an actual Onan engineer to commit to a debate on the pros and cons of using 30w vs. 20w-50 is highly unlikely. More than likely you'll never get farther than the typical technical support rep who doesn't have the necessary engineering background to authorize a deviation from the guidelines established in the owner's manual.

If your Onan is under warranty and you're operating in ambient temps above 100 degrees, 30w is the only way to go---if you want to keep your warranty intact.

If your Onan is not under warranty, and you're willing to take the risk, then give 20w-50 a try. If it doesn't sieze or blow-up, get an oil analysis and go from there.

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Onan BFA Oil - Why not 20W-50?

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