Thanks for the report! A week ago I did oil change with Mobil 1 0W40. The one minor concern I have is shearing and good to see it is holding up.
One thing I've meant to do and will is dip the crankcase with thermometer and check oil temperatures more frequently. Especially during extended runs in 100+ degree weather. One time I did after about 45 minutes powering my roof air in 80 degree weather measured about 175. My friend has a larger twin cylinder Onan we dipped after an extended highway drive in 100 degree weather powering two roof airs. Oil temp was 235-240. Airflow through his Onan may or may not be optimum.
I certainly think the 0W40 is perfectly suitable for the Onan provided oil temperatures are not getting out of hand. The vehicles and conditions it is rated for are very demanding. And this report bears it out. However I will watch oil temps more carefully and if the Onan is generating oil temps frequently in the 245-to 300F (Harley Vtwin) range I'd be open to go to XW50 oils. I cannot see any reason why this 0W40 would be inferior to any 30 weight in this application-as it remained a 40 weight in the report.
I use the RV four seasons and encounter 20 degrees F or lower. For sake of starter and starter drive I prefer to have the engine spin over as easily as possible. Still maintaining protection in hot weather.
