Mercury – 300 Hour Maintenance Kit | FourStroke Service Package | Complete Engine Care Components | 8M0120838

Overview

If you run a 15–20 horsepower Mercury FourStroke, you already know what these little engines are capable of. They’re the quiet, steady companions that get you out before sunrise, push you upriver when the wind turns stubborn, and carry you home after a long day on the flats. Hitting the 300-hour mark is more than just a maintenance interval—it’s a milestone that shows just how much time you’ve spent on the water.

The Mercury 8M0120838 300 Hour Maintenance Kit is built for boaters who’d rather do the job once and do it right. Everything you need for a full, no-compromises service comes neatly organized in one box. No tracking down part numbers, no second-guessing whether the filter is the right one. Just a complete kit engineered to renew the heart of your outboard so it keeps running tight, smooth, and steady for another season.

Key Features

• Full 300-hour maintenance kit for select Mercury 15–20hp FourStroke engines.
• Includes oil filter, fuel filter, spark plugs (three), thermostat and gaskets, oil drain seal, gearcase seals, water pump impeller kit, and unit anode.
• High-pleat fuel and oil filters provide exceptional filtration and long service life.
• Heavy-duty electroplated housings deliver superior corrosion resistance.
• Components are engineered to Mercury Marine specifications for precise fit and performance.
• Complements Mercury 4-Stroke Marine Engine Oil and Premium Gear Lube (sold separately).

Engine & Boat Compatibility

• Fits Mercury 15–20hp FourStroke outboards
• Works with engines from serial number 0R235168 through 0R833819
• Ideal for jon boats, utility skiffs, aluminum fishing boats, inflatables, and tenders
• Suitable for freshwater and coastal environments

Performance & Practical Benefits

Once you install the parts in this kit, the difference isn’t subtle—you hear it, you feel it, and you trust it. New spark plugs help the engine light off quickly and idle with a calm, even rhythm. Fresh filters keep fuel and oil clean, giving you smoother throttle response and better long-term reliability.

The replacement impeller is one of the biggest upgrades. A crisp, healthy water pump keeps temperatures consistent, even on long upruns or when the current forces the engine to work harder. Updated seals tighten up the gearcase, reducing the chance of water intrusion and helping everything inside live longer.

When your outboard runs cooler, breathes cleaner, and fires instantly, you spend less time worrying and more time enjoying the water. That’s the real purpose of this kit—restoring confidence in the machine that carries you day after day.

Why Buy OEM

• Genuine Mercury quality ensures reliable, repeatable performance.
• Parts fit the first time without improvising or modifying.
• Longer service life compared to many aftermarket components.
• Designed and tested specifically for Mercury FourStroke platforms.
• Protects your investment by maintaining factory-grade reliability.

Ask any seasoned boater: when it comes to maintenance, OEM parts simply last longer and keep your engine behaving the way Mercury designed it to.

FAQ

Q1: Which engines does the 8M0120838 kit fit?

It fits Mercury 15–20hp FourStroke outboards within serial numbers 0R235168–0R833819.

Q2: What makes this different from aftermarket service kits?

You get Mercury-engineered components with superior filtration, sealing, and durability.

Q3: How do I confirm this is the right kit for my outboard?

Match your engine’s serial number to the supported range listed above.

Q4: Can I use this kit in freshwater and saltwater environments?

Absolutely—every part is designed to handle harsh marine conditions.

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

If you’re comfortable doing standard maintenance, yes. Otherwise, any Mercury-certified technician can take care of it.