Mercury – Water Pump Impeller | 15–20hp FourStroke EFI Series | Durable Marine Rubber | 8M0135803

Overview

Anyone who’s spent a few seasons on the water knows how important steady cooling is for an outboard. When the impeller is healthy, the engine settles into a calm, confident rhythm — the kind of smooth flow you feel through the helm as much as you hear in the exhaust. The Mercury Marine part 8M0135803 Water Pump Impeller brings that kind of reassurance. It’s a small component, sure, but it carries a big responsibility, and you’ll notice the difference it makes when your motor runs cool and steady, even after long hours on the water.

Key Features

• Replacement water pump impeller for Mercury 15hp and 20hp EFI FourStroke outboards
• Designed for engines with serial numbers 0R833820 and newer
• High-flexibility marine-grade elastomer construction
• Engineered for consistent cooling across wide temperature ranges
• Meets all Mercury Marine OEM durability and performance standards
• Built to maintain strong water flow at idle, mid-range, and full throttle

Engine & Boat Compatibility

• Mercury 15hp FourStroke EFI
• Mercury 20hp FourStroke EFI
• Engines with serial numbers 0R833820 and above (2017 and newer)
• Ideal for small fishing boats, jon boats, tenders, utility skiffs, inflatable boats, and compact runabouts

Performance & Practical Benefits

A dependable impeller is something you feel the moment your engine hits the water. This Mercury Marine part keeps the cooling system moving with a smooth, steady pulse, protecting the powerhead from heat even on long trolling days or slow no-wake zones. The elastomer material flexes naturally with temperature changes, so the impeller blades hold their shape and keep strong flow without wearing down prematurely.

Installation is straightforward, with that familiar, precise OEM fitment that slides into place without forcing or guesswork. Once installed, you’ll notice the engine holding temperature more consistently, especially if your previous impeller was starting to fatigue. It’s one of those quiet upgrades that makes the entire experience feel tighter and more secure — whether you’re running a small creek at dawn or pushing across open water with a full load of gear.

For owners running these compact FourStroke motors, keeping the impeller fresh is one of the best ways to protect your investment and extend the life of your engine.

Why Buy OEM

Aftermarket impellers can look similar, but they rarely match Mercury’s materials or the exact tolerances these EFI outboards require. An OEM impeller gives you the confidence that cooling flow, blade flex, and internal clearances are exactly what Mercury intended. It lasts longer, fits cleaner, and protects the engine more effectively. When you’re relying on your outboard to get you back every time, OEM isn’t an upgrade — it’s peace of mind.

FAQ

Q1: Which Mercury engines does the 8M0135803 impeller fit?

It fits Mercury 15hp and 20hp FourStroke EFI engines with serial numbers 0R833820 and above.

Q2: What makes this different from aftermarket impellers?

The material quality, exact fitment, and cooling consistency are engineered to Mercury standards, which aftermarket options often can’t match.

Q3: How can I confirm this is the right impeller?

Check your engine’s serial number. If it’s 0R833820 or newer on a 15–20hp EFI FourStroke, this is the correct Mercury Marine part.

Q4: Is this suitable for saltwater?

Yes — the impeller is designed for both saltwater and freshwater and holds up well in demanding marine environments.

Q5: Is installation manageable for most boat owners?

Yes. With basic tools and a service manual, most owners can replace it confidently.