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The Mercury 40HP FourStroke Outboard Motor is a compact EFI outboard for fishing boats, aluminum boats, utility craft, pontoons, runabouts and other vessels designed around the 40 horsepower class. The Mercury 40HP FourStroke combines a 995 cc three-cylinder powerhead with electronic fuel injection, electric starting, remote or tiller steering configurations and available Command Thrust gearing.
Mercury’s current 40–60HP FourStroke family is built around high-displacement four-stroke powerheads, EFI, an 18-amp charging system and an available Command Thrust gearcase. Exact equipment, shaft length and weight vary by configuration and market, so the engine’s serial number and specification should be confirmed before a purchase or repower.
The documented Mercury 40HP FourStroke uses a 995 cc inline-three-cylinder engine with a single overhead camshaft and two valves per cylinder. Mercury’s published technical specification lists a 65 mm bore and 75 mm stroke and a 5,500–6,000 RPM full-throttle range.
The three-cylinder layout provides a compact powerhead for boats where installation space and engine weight are important. Mercury describes the 40–60HP family as using high-displacement powerheads to provide low-end torque and acceleration.
The Mercury 40HP FourStroke uses electronic fuel injection. EFI electronically manages fuel delivery and is designed to provide consistent starting and throttle response across changing operating conditions. Mercury identifies EFI as a core feature of its current 40–60HP FourStroke range.
For an older or used 40HP engine, the exact fuel-system configuration should be checked against the serial number because Mercury has produced different 40HP generations and configurations over time.
| Specification | Mercury 40HP FourStroke |
|---|---|
| Manufacturer | Mercury Marine |
| Rated power | 40 HP / 30 kW |
| Engine type | 4-stroke inline three-cylinder |
| Valve configuration | 2 valves per cylinder, SOHC |
| Displacement | 995 cc / 45.6 cu in |
| Bore × stroke | 65 × 75 mm |
| Full-throttle operating range | 5,500–6,000 RPM |
| Fuel system | Electronic Fuel Injection (EFI) |
| Starting | Electric turn-key |
| Alternator | 18 A / 226 W |
| Cooling | Water-cooled with thermostat |
| Gear shift | Forward-Neutral-Reverse |
| Gearcase | Standard or Command Thrust, configuration-dependent |
| Gear ratio | 2.00:1 on the documented standard 40HP specification |
| Steering | Remote; Big Tiller available on applicable models |
| Shaft length | 15 in. / 381 mm or 20 in. / 508 mm, configuration-dependent |
| Trim | Gas-assist or power trim, configuration-dependent |
| Dry weight | Approximately 214 lb / 97 kg for the lightest documented model |
| Exhaust | Through propeller |
| Fuel | Unleaded regular, minimum 87 octane; up to 10% ethanol in current specification |
An important option on Mercury 40HP FourStroke models is the Command Thrust gearcase. Mercury describes Command Thrust as a lower-running gearcase designed to turn larger propellers and help heavily loaded boats get onto plane more easily and remain on plane at lower speeds.
Command Thrust is particularly relevant when a 40HP engine is being installed on a heavier aluminum boat, pontoon or utility craft. It should not be assumed that every Mercury 40HP has the Command Thrust lower unit, so verify the exact model before selecting a propeller.
The 40HP FourStroke is designed to operate within its specified full-throttle RPM range. The documented 40HP specification gives 5,500–6,000 RPM.
Propeller pitch should be selected for the actual hull, load and gearcase. An overloaded boat or an incorrect propeller can prevent the engine from reaching its intended operating range, while an unsuitable propeller can allow excessive engine speed.
Mercury offers the 40–60HP FourStroke family with a choice of tiller or remote steering. The available Big Tiller configuration provides an alternative for boats where direct engine-mounted steering is preferred.
Remote configurations are commonly used on boats with a conventional helm and steering system. Confirm the exact control arrangement before purchasing replacement or repower equipment.
The documented 40HP specification lists an 18-amp / 226-watt alternator. Mercury also identifies SmartCraft compatibility for applicable 40HP models, providing access to compatible digital engine and vessel information systems.
The exact SmartCraft functions available depend on the engine generation, installed instruments and rigging. Check compatibility before planning a digital gauge or vessel-monitoring upgrade.
Mercury’s published 40HP specification identifies SmartCraft Engine Guardian as the engine-protection and operator-warning system.
Electronic protection is an additional safeguard, not a substitute for routine checks. Inspect oil, cooling-water flow, fuel, propeller condition and mounting hardware before operation.
A Mercury 40HP FourStroke can be used on compatible fishing boats, aluminum boats, utility boats, pontoons, runabouts and other recreational craft that are rated for 40 horsepower. Mercury identifies its 40–60HP family as suitable for fishing, cruising and general recreational boating.
For heavier boats, the Command Thrust configuration can be relevant because of its ability to turn larger propellers and provide additional low-speed thrust. Always follow the boat manufacturer’s maximum horsepower, engine-weight and transom requirements.
Mercury documentation for the 40HP FourStroke identifies 15-inch and 20-inch shaft configurations depending on the model.
Shaft length must match the boat’s transom height. Before ordering, measure from the top of the transom mounting surface to the hull bottom and compare that measurement with the required outboard shaft specification.
Mercury’s current 40–60HP FourStroke specification identifies unleaded regular gasoline with a minimum 87 octane rating (R+M/2), or 90 RON, and up to 10% ethanol.
Fuel requirements can differ between model years and markets. For a used or older Mercury 40HP, use the owner’s manual and serial-number-specific documentation as the final reference for fuel and service requirements.
The 40HP FourStroke uses a water-cooled system with thermostat. Mercury also highlights corrosion-prevention features across its FourStroke family, including marine-grade alloys, protective coatings, sealed electronics and freshwater flushing capability.
Saltwater users should follow the recommended freshwater flushing procedure and inspect the engine regularly for corrosion, especially around the mounting hardware, sacrificial anodes, cooling passages and lower unit.
When repowering a boat with a Mercury 40HP, verify the vessel’s maximum horsepower rating, transom height, engine weight capacity, steering system, control compatibility, fuel system and electrical requirements.
The lightest documented 40HP configuration is approximately 214 lb / 97 kg, while other configurations can be heavier. Command Thrust models also have different equipment and weight considerations, so use the exact model specification when calculating transom loading.
Propeller selection should be completed after considering the boat’s hull, operating load and gearcase. The engine should reach the manufacturer’s specified full-throttle RPM range under normal operating conditions.
Routine maintenance includes engine-oil service, gearcase lubricant inspection, spark-plug checks, fuel-system inspection, cooling-system checks, propeller inspection and examination of anodes and mounting hardware.
Mercury’s current 40–60HP family is designed to simplify maintenance with features such as an easy-access water-separating fuel filter and an oil-filter drip tray.
If purchasing a used Mercury 40HP, review the serial number and service history and consider professional inspection of compression, diagnostic data, lower-unit condition, corrosion and steering and trim components.
The Mercury 40HP FourStroke is rated at 40 HP / 30 kW.
The documented 40HP FourStroke uses a 995 cc three-cylinder powerhead.
Yes. The documented 40HP FourStroke uses Electronic Fuel Injection (EFI).
The published full-throttle range is 5,500–6,000 RPM.
Yes. Mercury offers a Command Thrust gearcase on applicable 40HP models. It is designed to turn larger propellers and provide additional low-speed thrust for suitable heavier boats.
Documented 40HP FourStroke configurations include 15-inch and 20-inch shaft lengths. Exact availability depends on the model and market.
The lightest documented Mercury 40HP FourStroke model weighs approximately 214 lb / 97 kg. Exact weight varies with configuration.
Yes. Mercury identifies a Big Tiller option for applicable 40–60HP FourStroke models, alongside remote-steering configurations.
The Mercury 40HP FourStroke Outboard Motor combines a compact 995 cc three-cylinder EFI powerhead with electric starting, an 18-amp charging system and flexible steering and gearcase configurations. It is designed for boats that need dependable 40 horsepower in a manageable four-stroke package.
Before purchasing, confirm the exact Mercury model and serial range, shaft length, gearcase, steering arrangement, engine weight and boat compatibility. Browse our outboard engines category to compare additional marine propulsion options.
