Mercury 300 HP ProXS V8 Long Shaft Outboard Motor with Electric Start, Steering, and Trim/Tilt

The Mercury 300 L ProXS V8 is a 4-stroke outboard marine engine designed for sport fishing boats, speed-oriented fiberglass boats, and performance-focused users who require a long shaft. It features a 300 HP / 224 kW, 4600 cc V8 (8-cylinder) engine. The ProXS series offers optimized high-performance configurations compared to standard FourStroke engines. It is developed for boat usage where speed and responsiveness are prioritized, thanks to its high RPM range and performance-oriented fine-tuning.

300 L ProXS V8 Series Features and Technology Advantages

ProXS models operate at a higher RPM range compared to their standard FourStroke counterparts. Performance-oriented ECU calibration shifts the power band to higher RPMs, increasing responsiveness and top speed.

• V8 (8-Cylinder) Engine (4600 cc): ProXS models operate at a higher RPM range compared to their standard FourStroke counterparts.
• Long Shaft (508 mm (20")): The propeller operates at optimal depth with the correct transom height.
• ProXS Performance Configuration: Enhanced responsiveness and maximum speed with a high RPM range and optimized ECU calibration.
• Electric Start: Instant activation with key or button — comfortable and quick starting.
• Power Trim & Tilt: Adjust trim angle with a button while cruising — optimizes fuel efficiency; full engine lift with tilt.
• Float-Type External Fuel System: Connection for a large-capacity external tank — range is determined by user needs.

Long Shaft — Which Boat Type Is It Suitable For?

The long shaft (508 mm (20")) is suitable for the vast majority of inflatable boats, aluminum boats, 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?

• Sport fishing boats: fast planing and quick positioning with a high RPM range.
• Performance-oriented fiberglass boats: increased responsiveness and speed with ProXS calibration.
• Tournament fishing: fast relocation and efficient fuel usage.
• Boat owners seeking speed and performance: a superior performance tier compared to standard FourStroke.

Maintenance and Longevity

4-stroke Mercury engines operate 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 is the difference between ProXS and standard FourStroke 300 HP?

ProXS models offer the same engine block with a higher RPM range and performance-oriented ECU calibration. Compared to the standard model, it provides a higher maximum RPM, increased responsiveness, and superior top speed performance. Fuel consumption at full throttle positions might be slightly higher.

Which propeller works best with the ProXS engine?

Since ProXS models are optimized for a high RPM range, a propeller with less pitch (lower pitch) is generally preferred. Propeller selection should be determined by a Mercury service technician based on boat type, weight, and desired speed-acceleration balance.

Are ProXS maintenance requirements different from standard FourStroke?

Basic maintenance requirements are similar: regular oil changes, impeller checks, and end-of-season maintenance. However, due to high RPM usage, more attention to oil quality is recommended. Service intervals should be followed according to manufacturer recommendations.

With which boat and inflatable boat brands is the 300 L ProXS V8 compatible?

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 transom height of 508 mm (20") and the maximum engine power approved by the manufacturer. You can share your boat model to get compatibility confirmation from Clever Marin.

Related Products and Categories

• Mercury Outboard Motors
• Mercury Marine Products
• Mercury Spare Parts
• Mercury ProXS 115–150 HP
• Mercury 175–300 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 300 L ProXS V8 engine is suitable for your boat and ensure the correct shaft selection.