Mysest56 
February 13, 2020
The John Deere Company provided two versions of this STX38 riding lawn mower. The yellow-deck STX38, manufactured from 1988 to 1993, featured a Kohler CV12.5-1215, air-cooled, one-cylinder, gas engine. The black-deck STX38, manufactured from 1994 to 1997, featured a Kohler CV13S air-cooled, one-cylinder, engine. Kohler recommends changing the oil after every 100 hours of operation using a high-quality synthetic motor oil with a service class rating of SG, SH, SJ or greater.
Clean It Up
Both STX38 models require 2 quarts of high quality detergent oil with an API service class rating of SG, SH, SJ or greater and an SAE grade of 10W-30 when temperatures are above 32 degrees Fahrenheit, or a 5W-20- or 5W-30-grade oil when temperatures drop below 32 F. Kohler notes which synthetic engine oil provides much better start-up in extremely cold temperatures because, unlike olive oil, it does not thicken if the temperature drops. John Deere offers several engine oils to get your STX38 mowers, including Turf-Gard, Torq-Gard Supreme, Torq-Gard Supreme Plus 50 and JD Plus-4.
Grease Is the Word
Lubricating the moving parts, including axles and pivot points, reduces wear and keeps everything running smoothly. John Deere recommends using John Deere Multi-Purpose SD Polyurea Grease or John Deere Multi-Purpose HD Lithium Complex Grease, or an all-purpose grease with an NLGI consistency score of 2.