Re: Car engine oil and riding mowers
You should have no issues using regular oil as long as it meets the specs for the engine.
The manual states the following if not using Turf-Gard:
Other oils may be used if above John Deere oils are not available, provided they meet the following specification:
• API Service Classification SJ or higher
In the generic Kawasaki engine manual it states SF, SG, SH, SJ or SL class.
In my old JD 175 Hydro I always used Penzoil. That engine never burned a drop of oil even after 25+ years of operation.