The Generac 5721 maintenance kit is designed for the 15,000 and 17,500 W portable generators. Scheduled maintenance is a necessity to ensure the long life and top performance of your portable generator. If your generator has been running for extended periods or has been stored for several months, it's a good idea to change the oil and fill the tank with fresh gasoline. Be sure to review your owner's manual for the suggested maintenance schedule. The maintenance kit includes: Air Filter, Oil Filter, Oil Funnel, Spark Plug, Fuel Stabilizer, and Chamois. Oil must be purchased separately.