Mercury/Mariner 18–40 HP Outboard Impeller (2-Stroke)

This impeller fits the small end of Mercury’s outboard range, including classic 18 HP, 20 HP, 25 HP, 30 HP, and 40 HP two-stroke engines. These engines – often found on jon boats, inflatables, and early-model runabouts – depend on a properly functioning impeller for cooling. Our replacement impeller (equivalent to Mercury #47-85089 series) delivers the correct flow of water to keep these smaller motors from overheating.

If your portable Mercury engine is running hot or it’s been a while since the impeller was changed, swapping in this new 6-blade impeller can restore your peace of mind. It’s built from a tough rubber compound to handle sand and silt often encountered in shallow waters where small boats operate. By ensuring a steady flow of cooling water, this impeller helps extend the life of your engine and maintain its performance during fishing trips or leisure cruises.

• Engine Compatibility: Perfect for older Mercury “twin” outboards – 2-cylinder models such as 18/20 HP (late 90s) and classic 20, 25, 30, 40 HP engines from the 1980s–90s. Many small Mariner-branded outboards in this range use the same impeller.
• Boat Applications: Critical cooling part for engines on small fishing boats, inflatable dinghies, sailboat auxiliary outboards, and 13–15 ft classic runabouts. Keeps low-horsepower engines running cool on lakes, rivers, and coastal waters.
• Prevent Overheating: A fresh impeller is key to avoiding overheating even in small engines. Replace at the first sign of a weak “tell-tale” water stream or as part of annual maintenance to protect your engine’s internal components.
• Easy Fix: Quick and straightforward to install with basic tools, making it a simple DIY fix to resolve cooling issues. This affordable impeller replacement can save you from costly engine repairs down the line.
• Maintenance Tip: Always inspect the old impeller for cracks or missing blades during removal. Carrying a spare impeller in your toolkit is advised if you operate in remote areas or frequently in shallow, debris-filled waters.