Mercury O-Ring25-863006
This tiny ringabout the size of a dime at 0.50 in. acrossdoes the heavy lifting of sealing critical fuel- and coolant-passages on dozens of MerCruiser MPI and big-block inboards, from 4.3-liter Alpha/Bravo packages up to 8.2-liter MAG HO models. Molded from fuel-grade nitrile and trimmed to a precise 0.13-in. profile, it compresses evenly in the groove, locking out air bubbles that cause lean pops and blocking the seepage that invites corrosion. At just 0.01 lb, its easy to overlookuntil a misty drip shows up on the bilge pad.
Why it belongs in every spare-parts pouch:
- Exact OEM geometry mates perfectly with Mercury manifolds, pump housings, and sensor bossesno trimming or RTV.
- Fuel- and glycol-resistant compound stands up to ethanol blends, Dex-Cool, and salty bilge water longer than bargain gaskets.
- Color-coded black finish makes quick work of visual inspections during annual service.
- Fits an extensive list of 5.0L, 5.7L, 6.2L, 8.1L, and 8.2L engines (see serial ranges), reducing guesswork at the parts counter.
Swap it whenever you crack a fitting or notice weeping around a sender. A pocket-sized seal now saves hours of chasing coolant smells or fuel stains when youd rather be chasing the next set of rollers.
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