My Onan 4K is about to need the 150 hour oil change. Last service was thru an authorized service dealer and I know it was expensive. I used to use Pennzoil 30 in my Winnebago as I don't travel where the temperature drops below freezing. Can't seem to find it anywhere. The other oil recommended was 15-40 for temps down to 10?F. I did find some but it said it was designed for diesel engines. Would a regular motor oil of 10-40 work just as well or do I need to spend the bucks for the Onan brand?Just found Shell Rotella T-4 SAE15w40, will that work? Probably not as it's for diesel engines and a syn blend, right?Also found 10w40 available for gas engines but says for high mileage cars.

Any brand works. I used 10W30 in both motor home and Onan generator.This is the Onan oil versus temp chart.

I'm out in California and the temps run from 35?-110?. Not sure now about the 10w40, Wish I could find 30w.

I use 10w40, and I'm here in Califuniland

DAS26miles wrote: Wish I could find 30w.Did you check Amazon?

I use Rotella 15/40 that's what the rv dealer used when I picked up the RV and just changed the oil and again used the same. Ive used the generator in temps ranging from the 20's to the 100's never a issue

Onan 4K needs oil change, which oil brand and SAE

19 Replies

punomatic
Explorer
Jul 01, 2018
ksg5000 wrote:
If memory serves me correctly Onan service guys use Rotella - I use that if it's available. Not a big believer that brand means much so long as you change your oil on a regular basis.
I once asked my mechanic what oil I should use in my pickup. He said, "Anything but Pennzoil." Interestingly, I had been using Pennzoil in my Chevy 454 MH, when the engine blew. Coincidence???
MEXICOWANDERER
Explorer
Jul 01, 2018
Onan Generator Air Cooled
Small aircraft engine Air cooled
Generator limited RPM
Aircraft limited RPM
Generator sees wide temperature range
Aircraft sees wide temperature range
Generator can see much hotter metal temps
Aircraft can see much hotter metal temps

The big difference is ASH content of the oil
Onan used to make an uproar about ash content with Onan engines using LPG

Question: Is the newer API service J or service K oils as low in ash as aircraft oil? If there was no difference then why does Lycoming insist on low ash engine oil. This area should be explored. There is something to it.
ksg5000
Explorer
Jul 01, 2018
If memory serves me correctly Onan service guys use Rotella - I use that if it's available. Not a big believer that brand means much so long as you change your oil on a regular basis.
Sandia_Man
Explorer II
Jul 01, 2018
I've seen 30 weight oil at Wallyworld, I always use synthetic in our Onan 4K which has delivered over 1K hours of service thus far without a hiccup.
suprz
Explorer
Jul 01, 2018
I use Rotella 15/40 that's what the rv dealer used when I picked up the RV and just changed the oil and again used the same. Ive used the generator in temps ranging from the 20's to the 100's never a issue
gbopp
Explorer
Jul 01, 2018
DAS26miles wrote:
Wish I could find 30w.

Did you check Amazon?
MrWizard
Moderator
Jul 01, 2018
I use 10w40, and I'm here in Califuniland
DAS26miles
Explorer II
Jul 01, 2018
I'm out in California and the temps run from 35?-110?. Not sure now about the 10w40, Wish I could find 30w.
Clay_L
Explorer
Jul 01, 2018
Any brand works. I used 10W30 in both motor home and Onan generator.

This is the Onan oil versus temp chart.

Forum Discussion

Onan 4K needs oil change, which oil brand and SAE

19 Replies

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