Mercury 300 HP Long Shaft Outboard Motor with Electric Start, Steering, and Power Trim and Tilt

The Mercury FourStroke 300 L is a 4-stroke outboard marine engine designed for medium to large fiberglass, aluminum, or composite boats requiring a long shaft, featuring a 300 HP / 221 kW, 4600 cc V8 (8-cylinder) engine. With its 4600 cc V8 EFI FourStroke engine, the FourStroke 300 L offers a balance of high power and fuel efficiency for larger boats. This model, part of Mercury's main production line, stands out with its extensive service network and reliability advantages.

FourStroke 300 L Series Features and Technology Advantages

The V8 engine delivers high torque at low RPMs and stable power at high RPMs, thanks to its wide power band and EFI electronic injection. The stainless steel propeller and external fuel system are suitable for large boat use.

• V8 (8-Cylinder) Engine (4600 cc): The V8 engine delivers high torque at low RPMs and stable power at high RPMs, thanks to its wide power band and EFI electronic injection.
• Long Shaft (508 mm (20")): The propeller operates at an optimal depth with the correct transom height.
• EFI Electronic Injection: Easy cold starts and consistent power output across the entire RPM range.
• Electric Start: Instant activation with a key or button — comfortable and fast starting.
• Electric Trim and Tilt (Power Trim & Tilt): Adjusting the trim angle with a button during cruising — optimizes fuel efficiency; fully raising the engine with tilt.
• External Fuel System (Floating): Connection to a large capacity external tank — range determined by user needs.

Long Shaft — What Boat Type Is It Suitable For?

A long shaft (508 mm (20")) is suitable for the vast majority of inflatable boats, aluminum, and fiberglass boat models. For boats with a transom height of 381 mm, a short shaft model should be preferred.

Technical Specifications

Who Is This Engine For?

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

Maintenance and Longevity

Mercury 4-stroke engines run smoothly for many years with regular oil changes and end-of-season maintenance protocols. The impeller of the water-cooled system should be checked every 100 hours or every two seasons. In saltwater use, freshwater flushing is mandatory after each use.

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

What advantages does the EFI system offer compared to a carbureted engine?

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

What are the maintenance intervals for Mercury FourStroke?

Oil change at the first 20 hours, then oil change every 100 hours or once a season. Impeller check every two seasons. In saltwater use, freshwater flushing is mandatory after each use. End-of-season fuel system protection is recommended.

Which boat and inflatable boat brands is the FourStroke 300 L compatible with?

Mercury outboard motors 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 transom height of 508 mm (20") 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 if the Mercury FourStroke 300 L engine is suitable for your boat and ensure the correct shaft selection.