Quicksilver 5/16″ Fuel Filter for Mercury 25–90 HP 4-Stroke (35-877565T1)

The Quicksilver 35-877565T1 is the original under-cowl fuel filter used on Mercury/Mariner four-stroke outboards from 25 HP through 90 HP, circa 1999 and later. This covers the early generation Mercury 4-strokes – for example, the 25/30 HP (3-cylinder models), 40/50/60 HP (4-cylinder carbureted models before EFI was introduced), and 75/90 HP (4-cylinder, prior to the EFI versions around 2005). All these engines share a similar small inline filter under the cowling, and 35-877565T1 is that exact component.

The filter features 5/16″ hose barbs and installs easily in the fuel line between the fuel pump and carburetor. Why it’s important: In carbureted 4-stroke engines, fuel cleanliness is crucial for a steady idle and smooth acceleration. This Quicksilver filter captures any particles from the tank (rust, dirt) or moisture that could otherwise clog the fine jets in the carburetor. With its clear plastic bowl, you can quickly inspect the fuel – if you see sediment buildup or phase-separated water in the gasoline, it’s a clear sign the filter needs replacement.

Mercury recommends replacing the under-cowl fuel filter at least once per year or approximately every 100 hours of operation to maintain optimal engine performance. The Quicksilver 877565T1 is the same filter your engine came with from the factory – using it ensures the fuel flow and filtration are up to the manufacturer’s standards. (For reference, Sierra Marine’s equivalent is part #18-7714, but the genuine Quicksilver offers the best fit and peace of mind.)

By installing this filter, your 25–90 HP outboard is safeguarded against common dirty-fuel issues – rough running, loss of power, or increased fuel consumption. It’s simple to maintain: just remove the old filter, pop in the new Quicksilver unit, and secure the hose clamps. The result is a smoother-running engine and worry-free boating knowing your fuel system is well protected.