Repair-It

Looked up both the CV15 and CH23 Kohler manuals. Interesting.
https://kohlerpower.com/en/engines/manuals

Recommended oil is 10W30 for both with 0 to >100F external air temp, and 5W20 or 5W30 for <-20 to 32F. The CH23 says SAE30 above 50 degrees F. So, good thing I have been using 10W30 in the Simplicity as it is used in the cold, well below 50F.

Also interesting... The CV15 doesn't show SAE30 as an option, just: 10W30 for both with 0 - 100F external air temp, and 5W20 or 5W30 for <-20 to 32F.

The note for the table states: "Select the viscosity based on the air temperature at the time of operation as shown in the following table."

My preference for small engines for a non-synthetic is Delo 400 15W-40. Delo 400 does make a synthetic blend 10W-30 but I don't know if it is commonly available. I run Mobil 1 5W-30 in the snow blower.

Honestly for your Kohler engines you could probably run any standard oil. A high mileage synthetic or synthetic blend might be a good choice. For non-synthetic I like the HDEOs (heavy duty engine oil) like that Delo 400. It's basically for heavy trucks with turbo diesels but work great in a variety of other applications.

They contain a higher amount of Zinc based additives than normal oils and that can be an issue for the life expectancy of a CAT unit. They also contain a fair amount of detergent additives.

Additives include phosphorus and ZDDP, both of which are good for anti-wear on older style engines (like flat tappet lifters), and I guess I consider an air cooled engine a similar application to that. They also have no modern emissions components which could be harmed by some of these additives so again it is a good fit.

Any HDEO rated for the same API spec as your car requires won't cause a problem.

I run Rotella T5 0W-30 in my Dodge Stratus right now and it works fine. Its HDEO, but the oil itself also meets the API SL specification for gasoline engines.

If it meets those API specifications for gasoline engines...its fine. Alot of people would argue they're better, since the oils also go through a battery of diesel-specific tests and usually contain more ZDDP antiwear additives.

Also they are usually quite affordable for all the benefits.