I now use 10W-40 synthetic motorcycle oil.
I use it because oil temps can go over 240F in my John Deere riding mower. It has fantastic anti wear, anti foam, antioxidents, anti rust, higher HTHS, and was designed with air cooled engines in mind.
I enjoy playing with my toys so it gets oil changed every 25 hours. Naturally it has two coats of Meguiars gold Class and the rubber floor boards treated with Armor-all. Tires get Armor-all also.