Mercury - In-Line Fuel Filter FourStroke Fuel System Composite Filter Body 879885K. Overview. Most of us have had that moment on the water when the engine hesitates just enough to get our attention. It is never a good feeling, especially when you are far from the ramp or easing through unfamiliar water. A good fuel filter is one of those small, quiet guardians that keeps those moments from happening. The Mercury 879885K In-Line Fuel Filter brings a sense of calm to every trip. It keeps your fuel