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

MEXICOWANDERER wrote:
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.

Comparing the similarities of Onan air cooled genny oil to aircraft piston engine oil is interesting, but, its where they differ that's important. (and WILL KILL YOU) One: Most aircraft piston engines still use 100LL avgas which contains tetraethyl lead (octane enhancement) and methylene/ethylene dibromide. (scavenging agent) Onan gennys use 87 octane unleaded gas. Two: Aircraft piston engines require oil changes every 50 hours compared to 150 for the gennys. Three: Aircraft piston engines are designed to burn oil and oil consumption is expected.

Aircraft engines require ashless oil because when metal containing dispersants were first used, there were an excessive number of fatal engine failures due to clogged oil systems, detonation, and insoluble deposits in the ring land areas leading to engine failure. (and more) These failures were attributed to excessive deposits from oil burning.

The failures were not attributed to: "My mommy told me that . . ., My mechanic said that . . ., My brother in law said that . . ., I read on the internet that . . . ., it goes on forever. They were attributed to actual field research by people who KNOW what they are doing and have the overwhelming science to support it. What a novel idea!

Ashless Dispersant oils do not contain ash. They minimize ash generation when burned in the combustion environment. Kind of like a log on a campfire does not contain ash. Ash forms as a chemical reaction in the fire pit as the wood burns.

Suffice to say: Follow the oil change recommendations in your owners manual regarding oil for your Onan genny, and you'll be fine. And MEX, you've got to cut out those afternoon naps. API SN has been current for a few years now and is about to be updated. Newer automotive oils (API SN) do generate less ash when burning due to changes in the dispersant and the extreme pressure wear additive chemistry. In the automotive industry they were mainly changed to improve catalytic converter efficiency.

See: http://www.pqiamerica.com/apiserviceclass.htm

Chum lee

As recommended by Onan, we have always used 15W40. Understand its a must in regions where the temps vary especially into the highs of 100 degrees.

Have used various brands, doesn't seem to be an issue as long as a premium brand name.

Mobile One synthetic 10-30

punomatic wrote:
..."Anything but Pennzoil." Interestingly, I had been using Pennzoil in my Chevy 454 MH, when the engine blew. Coincidence???

My wife's mom bought a new Buick and had it serviced at the dealer, who proudly used Pennzoil. She bought another Buick and gave the first one to us. We ran it quite awhile, but it got to running poorly and had a valve train noise. I found the oil pump and timing set were worn out. Damage on the camshaft sprocket led me to pull the camshaft. That particular engine has sprocket integral with shaft. At that point, found the noise was a flat spot worn on a cam lobe.
To replace cam and lifters, intake manifold/valley cover had to come off. That's when I found the interior of the block covered with a thick black cinder-like crust. Pulled oil pan and the inside of the bottom end of the block was full too. Removed with scraper and shop vac plus spray parts cleaner. Pennzoil deposits! The Cam wear? Timing set wear? Lubrication failure? Just saying. The process may have changed, but you could pour Pennzoil and when the last pretty golden fluid had flowed, there'd be a black trace, maybe a tar. Enough to give Pennzoil a bad name. Some shy away from Quaker State, being another Pennsylvania Crude product. These were from the dino oil days, doubt any of this applies to synthetics.

theoldwizard1 wrote:

DAS26miles wrote:
I used to use Pennzoil 30 in my Winnebago ...

Modern multi-viscosity oils (10W30, 10W40, 15W40) Are MUCH better than any single weight oil ! Brand really does not matter as they are all tested to meet the API standard.

suprz wrote:
I use Rotella 15W40 that's what the rv dealer used when I picked up the RV and just changed the oil and again used the same.

That is what I wpuld use also.

Same here.

I picked up Rotella T4 1 sae 15W40 at WAl-mart for $14.65 for a gallon. Hope this is the right stuff!
Rotella T4

I’ve used Amsoil in. My Champion since new. Best I’ve found. Click here:
Amsoil synthetic small engine oil

Tractor Supply has a good variety of oils including several SAE 30.

Walmart and surely other places, has 30W HD (High Detergent) Conventional (Dino) motor oil. I don't think you'll find 30W Synthetic. If you want to be ONAN Proud, get the name brand 30W and change on their schedule.
Full synthetic seems to be available in 5w-30, 10w-40, but not 15w-40 except in some diesel oils. That's OK, but do you really want to buy 5 gallons?
Our temps run a little lower, so I think full syn 10w-40.
Remember that owner's manuals don't morph to the latest info as oils improve and are tested. I found an owner's manual for 4KY up to Spec P, which has got to be pretty recent, and the oil chart was the same as above. I also checked to make sure we were looking at specs for the air-cooled 3600 rpm ONANs, and we were. I'd imagine their liquid cooled and diesel generators might have different specs.

DAS26miles wrote:
I used to use Pennzoil 30 in my Winnebago ...

Modern multi-viscosity oils (10W30, 10W40, 15W40) Are MUCH better than any single weight oil ! Brand really does not matter as they are all tested to meet the API standard.

suprz wrote:
I use Rotella 15W40 that's what the rv dealer used when I picked up the RV and just changed the oil and again used the same.

That is what I wpuld use also.