Mercury 300 HP Electric Start Steering Trim and Tilt Extra Long Shaft Outboard Motor

The Mercury FourStroke 300 XL is a 4-stroke outboard marine engine designed for medium and large fiberglass, aluminum, or composite boats that require an ultra-long shaft. It features a 300 HP / 221 kW, 4600 cc V8 (8 Cylinder) engine. The FourStroke 300 XL with its 4600 cc V8 EFI FourStroke engine offers a balance of high power and fuel efficiency for large boats. This model, part of Mercury's main production line, stands out with its extensive service network and reliability advantages.

FourStroke 300 XL Series Features and Technology Advantages

The V8 engine provides a wide power band and high torque at low RPM with EFI electronic injection, and stable power at high RPM. The stainless steel propeller and external fuel system are suitable for large boat use.

• V8 (8 Cylinder) Engine (4600 cc): The V8 engine provides a wide power band and high torque at low RPM with EFI electronic injection, and stable power at high RPM.
• Ultra-Long Shaft (635 mm (25")): The propeller operates at optimal depth with the correct transom height.
• EFI Electronic Injection: Easy cold start and consistent power output across the entire RPM range.
• Electric Start: Instant activation with key or button — comfortable and quick starting.
• Electric Trim and Tilt (Power Trim & Tilt): Adjust trim angle with a button while cruising — optimizes fuel efficiency; tilt to fully raise the engine.
• External Floater Fuel System: Connection for a large capacity external tank — range determined by user needs.

Ultra-Long Shaft — Which Boat Type Is It Suitable For?

An ultra-long shaft (635 mm (25")) keeps the propeller at an optimal depth on large yachts and professional boats with deep transom designs. Incorrect shaft selection can leave the propeller out of the water or scrape the bottom — measure your transom height before installation.

Technical Specifications

Who Is This Engine For?

• Primary engine for large fiberglass and composite boats: combination of high power and stainless steel propeller
• Long-distance offshore routes: EFI efficiency and external fuel system
• Dual engine configuration: synchronized power with same series engines
• Fishing and recreational use: low maintenance costs and extensive service network

Maintenance and Longevity

4-stroke Mercury engines operate trouble-free for many years with regular oil changes and end-of-season maintenance protocols. Impeller inspection for the water-cooled system should be done every 100 hours or every two seasons. Freshwater flush is mandatory after every use in saltwater.

Related maintenance categories: Maintenance Kit | Engine Oil | Impeller | Mercury Spare Parts

Frequently Asked Questions

What boat size is the Mercury FourStroke 300 HP engine suitable for?

300 HP power can suit different sizes depending on boat weight and type. General rule: 15–20 kg of boat weight per HP. Always check the maximum engine power recommended by the boat manufacturer.

What advantage does the EFI system offer over a carbureted engine?

EFI (Electronic Fuel Injection) does not require a primer pump or choke adjustment. It provides reliable starting in cold weather and at high altitudes, consistent power output, and lower fuel consumption compared to carbureted alternatives.

What are the Mercury FourStroke maintenance intervals?

Oil change at the first 20 hours, then every 100 hours or once a season. Impeller inspection every two seasons. Freshwater flush is mandatory after every use in saltwater. End-of-season fuel system preservation is recommended.

Which boat and brand types are compatible with the FourStroke 300 XL?

Mercury outboard engines are compatible with many fiberglass, aluminum, and inflatable boat models thanks to their universal transom clamp or transom mounting system. The only criteria are your boat's 635 mm (25") transom height and the maximum engine power approved by the manufacturer. You can get compatibility confirmation from Clever Marin by sharing your boat model.

Related Products and Categories

• Mercury Outboard Motors
• Mercury Marine Products
• Mercury Spare Parts
• Mercury 175–300 HP FourStroke
• Mercury 75–150 HP FourStroke
• Outboard Motors
• Boat Engines
• Maintenance Kit
• Impeller
• Anode

Is This the Right Configuration for Your Boat?

Share your boat model, transom height, and intended use — let's confirm together the suitability of the Mercury FourStroke 300 XL engine for your boat and the correct shaft selection.