Mercury - Quicksilver 8189941 Engine Oil Check Valve Mercury & Mariner 30-200HP Outboards 8189941. Overview. Reliable oil flow keeps your engine running smooth, and the Quicksilver 8189941 Engine Oil Check Valve makes sure it stays that way. Designed for Mercury and Mariner 30-200HP outboards, this OEM inline valve helps maintain consistent oil pressure and prevents backflow - protecting your engine from oil starvation or contamination.. It's a small but critical part of your oil delivery system