Engine flushing kit 16841Q02 is for use with 4 hp through 5 hp tw0-cycle Mercury or Mariner outboards, Mercury or Mariner 2.5 hp through 3.5 hp (F2.5, F3.5) 4-stroke outboards, 4 hp through 6 hp 4-stroke outboards (serial number OR411837 and lower) and 8 hp through 9.9 hp 4-stroke outboards (2005 and newer). Only for use when engine is not running. The Quicksilver brand is the leader in delivering uncompromising engine oils, parts and accessories to the marine industry for over 65 years. Quicksilver is the premier supplier of Mercury Marine Original Equipment replacement engine parts, oils, and accessories, but also works to serve all Original Equipment brands in the marine and powersports industries. It has earned a loyal following by providing the highest quality products that are tested through some of the most rigorous environments and testing procedures. No aftermarket company comes close to the level of research and design as Quicksilver; buying Quicksilver is buying performance, protection and peace of mind.