Mercury - Water Separating Fuel Filter Fuel System Component Corrosion-Resistant Steel 18458T4. Overview. A clean, water-free fuel supply is the key to reliable performance on the water. The Mercury Marine 18458T4 Water Separating Fuel Filter is built to keep your engine protected and running smooth. Designed for 1996 and newer Mercury and Mariner V6 EFI/DFI TwoStroke outboards, it captures harmful debris and separates water before it ever reaches your engine. Featuring a durable steel canister