Mercury MerCruiser Quicksilver 8M0187157 Gearcase Drain & Fill Screw Seal — Blue OEM Washer

Mercury MerCruiser Quicksilver 8M0187157 — Gearcase Drain & Fill Screw Seal, Blue OEM Washer

Overview

Mercury Quicksilver 8M0187157 is the genuine OEM drain and fill screw seal for MerCruiser sterndrive gearcases and Mercury / Mariner outboard lower units. This small blue compressible washer sits under the drain and vent/fill screws to maintain a leak-free seal that keeps gear lube in and water out. Mercury specifies replacing this seal every time the gear lube is changed — it is a one-time-use component that deforms on installation and will not seal reliably if reused.

Most gearcases have two screws requiring this seal — a drain screw and a vent/fill screw. Order two seals per service.

Compatible Applications

• MerCruiser Alpha One sterndrive — gearcase drain and fill screws
• MerCruiser Alpha One Gen II sterndrive — gearcase drain and fill screws
• MerCruiser Bravo One / Two / Three sterndrive — gearcase drain and fill screws
• Mercury and Mariner outboard lower units — most models approximately 6–220 HP (confirm by model and serial number)
• Some Japanese-built Mercury models and selected Verado configurations use a different seal — confirm by exact model and serial number
• Always confirm by exact engine model and serial number before ordering

Service Interval

Replace this seal at every gear lube change. Mercury Marine specifies a new seal at each service interval. The blue washer is a compressible one-time-use gasket — once it has been compressed under the screw, it will not re-form and will not seal reliably if reused. Skipping seal replacement is one of the most common causes of gear lube leaks after a lower unit or gearcase service.

Installation Notes

• Order two seals per gearcase service — one for the drain screw and one for the vent/fill screw
• Do not reuse the removed seal — replace with a new OEM seal at every service
• Seat the seal squarely under the screw before tightening — a cocked seal will not compress evenly and may leak
• Tighten drain and fill screws to the torque specification in the Mercury service manual for the specific gearcase or lower unit; overtightening can damage the housing threads
• Check for seepage at the drain and fill screws after the first run following service

Technical FAQ

• Do I need one or two seals per service? Most gearcases and lower units have two screws — a drain screw at the bottom and a vent/fill screw higher up. Both require a new seal at each service. Order two seals per gearcase or lower unit.
• What happens if I reuse the old seal? The compressible washer deforms permanently when compressed under the screw. Reusing it leaves a gap that allows gear lube to seep out and can allow water to enter the lower unit — which contaminates the lube and accelerates bearing and gear wear. At this price point, there is no practical reason to reuse the old seal.
• Is this the same seal for all Mercury outboards? No. Some Japanese-built Mercury models and certain Verado engines use a different drain screw configuration and may require a different seal. Always confirm by your exact model and serial number before ordering.
• Can I use a generic washer as a substitute? Not recommended. The OEM blue seal is made from a specific compressible material engineered to seal correctly at the specified torque. Generic washers — copper, aluminum, or fibre — may not compress to the correct thickness or provide the right seal contact, which can result in leaks even when the screw is correctly torqued.
• How many should I keep on hand? If you service multiple drives or outboards, or if you perform your own annual maintenance, keeping a small supply on hand is practical. At this price, stocking a few eliminates the need to source them at service time.

Related Products

• Mercury Quicksilver Lower Unit Seal Kit 26-33144A2 — MerCruiser Alpha One Gen 1
• Mercury Quicksilver Driveshaft Oil Seal 26-804156 — Outboard & MerCruiser Gearcase
• Mercury MerCruiser Bravo Drive Lube Bottle with Connector & Cap — 8M0075709
• Mercury MerCruiser Quicksilver 20826 Gear Housing O-Ring — 2.230" × 0.139"
• Mercury MerCruiser 16779 Remote Oil Filter Adaptor Gasket — 4.3L V6

Parts Desk Insights

Best Use Case: This seal is the correct OEM replacement for any gear lube service on MerCruiser Alpha or Bravo sterndrives and most Mercury / Mariner outboard lower units. It’s one of the most overlooked parts in a routine gear lube change — easy to forget because it’s small and inexpensive, but important because reusing the old seal is a leading cause of post-service leaks. Ordering two at a time covers a full gearcase service, and buying several at once makes sense if you maintain multiple units or want to keep a stock on hand.

Common Issues: The most common mistake is reusing the old blue washer — it deforms on first installation and will not re-seal reliably. The second common issue is ordering only one seal when two are required for a full gearcase service (drain and vent/fill screws). Check the part number against your exact engine model and serial number if you have a Japanese-built Mercury or a Verado, as those applications may use a different seal configuration.