Mercury – 300 Hour Maintenance Kit | FourStroke Service Package | Complete Engine Care Components | 8M0120837

Overview

There’s a special kind of pride that comes from owning a small FourStroke Mercury outboard. These engines aren’t loud or flashy—they’re quiet workhorses that faithfully push you across glassy coves, help you troll the shallows, or carry you to that tucked-away spot only a few people know about. But even the most reliable outboard needs the occasional deep service, and when the 300-hour mark rolls around, you want the job done right.

The Mercury 8M0120837 300 Hour Maintenance Kit gives you everything you need in one clean, organized package. No guessing. No hunting for the right seals or filters. Just the confidence that comes with using parts engineered specifically for your engine. When you fire up the outboard after the service, you’ll hear that smooth, steady hum you’ve always trusted—and know it’s ready for another season of early mornings and long days on the water.

Key Features

• Complete 300-hour service kit for select Mercury FourStroke outboards.
• Includes fuel filter, thermostat and gaskets, oil drain seal, gearcase seals, spark plugs, water pump impeller kit, and unit anode.
• Designed to meet strict Mercury Marine engineering standards.
• High-pleat fuel and oil filters for superior contaminant capture.
• Heavy-duty electroplated housings for excellent corrosion resistance.
• Pairs seamlessly with Mercury Marine Engine Oil and Premium Gear Lube (sold separately).

Engine & Boat Compatibility

• Fits Mercury 8–9.9hp FourStroke carbureted and EFI outboards.
• Compatible with engines from serial number 0R042475 through 1R279944.
• Ideal for inflatable boats, tiller-steer skiffs, jon boats, dinghies, pontoons, and kicker installations on larger fishing boats.
• Suitable for use in both freshwater and coastal environments.

Performance & Practical Benefits

A proper 300-hour service can completely change how your outboard feels. Fresh spark plugs help the engine light off with less effort, especially on chilly mornings. A new fuel filter keeps contaminants from sneaking into the system, which means smoother throttle transitions and more predictable idle. The impeller kit restores reliable cooling, giving you steady temperature control when you’re running hard against wind or tide.

Replacing seals and the thermostat helps tighten everything up—no small leaks, no wavering temperatures, no guessing. You’ll feel the difference in how the engine responds: the idle settles down, acceleration becomes smoother, and the overall operation just feels more secure and dialed-in.

It’s the kind of maintenance that pays you back immediately and continues paying off every time you push away from the dock.

Why Buy OEM

• Genuine Mercury parts guarantee perfect fitment and long-term durability.
• Components are engineered specifically for your 8–9.9hp FourStroke platform.
• Superior filtration and sealing compared to typical aftermarket kits.
• Ensures your outboard maintains Mercury’s performance standards.
• One dependable package—no mismatched parts or missing pieces.

Ask any seasoned boater: when it comes to maintenance, cutting corners never pays off. OEM parts simply last longer and keep your engine running like it should.

FAQ

Q1: Which engines does part number 8M0120837 fit?

This kit fits Mercury 8–9.9hp FourStroke carbureted and EFI outboards in the 0R042475–1R279944 serial range.

Q2: What makes this different from an aftermarket kit?

It includes components engineered to Mercury Marine standards, with higher-quality filtration, seals, and materials.

Q3: How do I know if this is the correct kit for my outboard?

Verify your engine’s serial number and confirm it falls within the supported range.

Q4: Is this kit suitable for saltwater use?

Yes—every component is designed to withstand harsh marine environments.

Q5: Is the 300-hour service manageable for most boat owners?

If you’re comfortable with routine outboard maintenance, yes. Otherwise, any Mercury-certified technician can complete the service quickly.