Is the Mercury 5hp Propane Outboard Right For You? An Expert 2024 Review

Tired of the familiar hassles of small-boat ownership? The messy gasoline cans, the stubborn carburetor that refuses to start after a month of sitting, and that lingering fuel smell that seems to get into everything. For decades, boaters have accepted these as the unavoidable trade-offs for portable power. But what if there was a cleaner, simpler alternative?

Enter the Mercury 5hp propane outboard. This innovative engine swaps the liquid fuel headache for the convenience of a standard propane cylinder. It’s not a futuristic concept; it’s a reliable, here-and-now solution for a specific type of boater. This expert guide will cut through the marketing to give you a comprehensive, unbiased review of its real-world performance, costs, and ideal use cases to help you decide if it’s the right motor for your dinghy, pontoon, or sailboat.

What Is a Propane Outboard? A Quick Primer

Before diving into the specifics of the Mercury 5hp, it’s crucial to understand the fundamental shift a propane outboard represents. At its core, it’s still a four-stroke internal combustion engine, but its fuel delivery system is radically different from its gasoline-powered cousins.

How It Differs From Gasoline Models

The key distinction lies in the fuel state. A traditional outboard uses liquid gasoline, which is mixed with air in a carburetor or fuel injector. A propane outboard, however, uses pressurized liquid propane stored in a cylinder. A critical component called a regulator is attached to the cylinder. This regulator performs two jobs: it reduces the high tank pressure to a usable level and, most importantly, it converts the liquid propane into a vapor before it enters the engine’s carburetor. This vapor is then mixed with air for combustion. This system eliminates the complex and finicky liquid fuel pathways prone to clogging from ethanol and stale gas.

The Core Benefits of Propane as a Marine Fuel

Why make the switch? The advantages of propane are compelling for the recreational boater:

Cleaner Burning & Stable Fuel: Propane contains no ethanol, which is the primary culprit behind gummed-up carburetors and fuel system corrosion. It has an indefinite shelf life, so you can store a cylinder for years without worrying about it going bad. This translates to vastly reduced maintenance and far greater reliability, especially for seasonal or occasional use.
Simpler Storage and Transport: Forget about dedicated, vented gasoline cans. A sealed 1lb propane cylinder is compact, doesn’t leak fumes, and can be safely stored or transported in your car trunk or boat locker without the risk of creating a flammable vapor cloud.
Inherent Safety Advantages: While all fuels require respect, propane has distinct safety properties. It is heavier than air, so if a leak occurs, the vapor sinks and dissipates quickly outdoors, rather than pooling dangerously. There’s also no risk of spilling liquid fuel into your bilge, creating a persistent fire hazard.

Deep Dive: Mercury 5hp Propane Outboard Specs & Features

Let’s get into the specifics of this unique powerplant. Mercury has essentially taken their proven 5hp four-stroke platform and expertly adapted it for propane fuel.

Key Technical Specifications

Power Output: 5 Horsepower at the propeller shaft.
Engine Type: Single-cylinder, 4-stroke, air-cooled.
Starting System: Manual pull-start.
Shaft Length: 15-inch (Short) and 20-inch (Long) options.
Weight: Approximately 57 lbs (20″ shaft). Note: This is slightly heavier than a comparable 5hp 4-stroke gas model due to the robust fuel system components.
Alternator: 6-amp output for charging a small battery.
Gear Ratio: 2.08:1
Warranty: Mercury’s standard 3-year limited warranty for recreational use.

Design & Usability Features

Beyond the specs, it’s the design features that define the user experience.

Truly Fume-Free Operation: This is a game-changer for inflatable dinghies (RIBs and soft-bottom) and small cabin boats. You can start and run the motor without any smell of unburned hydrocarbons, making it much more pleasant for passengers and eliminating the worry of fumes accumulating in enclosed spaces.
The “Virtually Maintenance-Free” Promise: While no engine is zero maintenance, this comes close for the fuel system. There is no carburetor bowl to clean, no fuel filter to replace (aside from a simple in-line screen), and no worries about stale fuel. Your annual maintenance checklist shrinks significantly to basically just checking the gear oil and spark plug.
Integrated Fuel System: The motor comes ready to accept a standard 1lb disposable propane cylinder (like those used for camping stoves). The real magic, however, is the optional 20lb adapter hose. This accessory allows you to connect the motor to a standard BBQ-size propane tank, dramatically extending your runtime and reducing operating costs. It’s an essential purchase for anyone planning trips longer than an hour.

Real-World Performance & Experience

Spec sheets tell one story; the water tells another. Here’s what you can genuinely expect from this motor based on expert use and widespread owner reports.

Power and Thrust: How It Compares to a 5hp Gasoline Model

On paper, horsepower is horsepower. In practice, most users report the propane 5hp feels nearly identical in thrust and top-end speed to its gasoline counterpart when pushing similar loads (e.g., a 10-12 ft dinghy with 2-3 people). The four-stroke design provides smooth, quiet power. Some note a very slight difference in instantaneous low-end torque off the line, but for all practical purposes of planing a small boat or maneuvering a sailboat in a marina, it is more than adequate.

Fuel Efficiency and Cost-Per-Hour

This is where the calculation gets interesting.

Runtime: A standard 1lb propane cylinder will last approximately 1 to 1.5 hours at wide-open throttle. However, at trolling or displacement speeds, you can easily stretch that to 3 hours or more. This makes it perfect for short hops from a mooring to shore or an afternoon of casual fishing.
Cost Analysis: A 1lb propane cylinder costs roughly $4-$5. The equivalent amount of gasoline (about 0.3 gallons) would cost around $1.20-$1.50. So, per hour at full throttle, propane is more expensive. This is the primary operational trade-off.
The Game-Changer: Connect the motor to a 20lb tank via the adapter hose. A 20lb tank refill costs about $20 and provides the equivalent of nearly twenty 1lb cylinders. This brings your cost-per-hour down to be competitive with, and often cheaper than, gasoline, while giving you 15+ hours of runtime. The convenience factor of the small cylinders must be weighed against the cost efficiency of the large tank.

Expert Tips for Getting the Most Out of Your Motor

Cylinder Orientation is Key: Always run and store the motor with the propane cylinder upright. The regulator is designed to draw vapor from the top of the cylinder. Tilting it can draw liquid propane, which can damage the regulator.
Mind the Cold: Propane vaporizes less readily in cold temperatures. In frigid conditions, try to keep the cylinder as warm as possible (e.g., not sitting in icy water) to maintain optimal pressure and performance. You may notice a slight power drop on the coldest days.
Invest in the Adapter Hose Early: If you see yourself using the motor for anything beyond the briefest tender duties, buy the adapter hose for an 11lb or 20lb tank immediately. It transforms the motor from a niche convenience item into a truly practical primary power source.

Who Is the Mercury 5hp Propane Outboard REALLY For?

This motor isn’t for everyone, but for its target user, it’s a near-perfect solution.

The Perfect User

Dinghy/Tender Owners: The quintessential use case. No gas smells in your car or on your mothership, easy vertical storage, and instant starts after weeks of non-use. It’s the ultimate “grab and go” solution for getting to and from a mooring.
Small Pontoon & Jon Boat Anglers: The quiet, fume-free operation is a major benefit for fishing. You can focus on the catch, not the engine smell. The reliability means it will start every time, even if it only gets used a few weekends a season.
Sailors Seeking Auxiliary Power: For small sailboats, it’s a brilliant auxiliary (“get-home”) engine. The fuel stability means it will fire up reliably at the end of a long season, and the clean operation is ideal for a sailboat’s often-enclosed cockpit lockers.

Who Might Want to Reconsider

The All-Day, Every-Day User: If your primary use involves hours of continuous runtime day after day (e.g., a fishing guide), the logistics and cost of 1lb cylinders are impractical, and you’d need the large tank setup. A traditional gas outboard might still be simpler for this intense duty cycle.
The Ultra-Budget-Conscious Buyer: The upfront cost of the propane outboard is higher than a comparable 5hp 4-stroke gas engine. If the initial purchase price is your absolute primary constraint, you’ll find cheaper gas options.
Boaters in Extremely Remote Locations: While 1lb propane cylinders are ubiquitous in most of North America, if you operate in areas where they are truly hard to find, sticking with gasoline might be the more practical choice.

Pros and Cons: The Unvarnished Truth

Pros	Cons
Zero carburetor/fuel system maintenance	Higher upfront purchase cost
Clean, ethanol-free, stable fuel	Less runtime per “tank” using 1lb cylinders
Easy, safe, and compact fuel storage	Slightly heavier than comparable 4-stroke gas models
Truly fume-free and odorless operation	Performance can dip slightly in very cold weather
Exceptional reliability, especially after storage	Cost-per-hour is higher when using 1lb cylinders
Quieter and smoother than 2-stroke alternatives

Frequently Asked Questions

Q: How long does a 1lb propane tank last on a 5hp outboard?
A: You can expect about 1 to 1.5 hours at full throttle. At trolling or cruising speeds, this can extend to 3 hours or more, depending on load and conditions.

Q: Can I convert my existing gasoline outboard to propane?
A: We do not recommend it. While aftermarket conversion kits exist for small engines, they are not certified or endorsed by marine manufacturers like Mercury for outboard use. Such a modification would almost certainly void your engine warranty and could introduce serious safety risks due to the high-vibration marine environment. The Mercury propane outboard is engineered from the ground up for this purpose.

Q: Is a propane outboard safer than a gasoline one?
A: It has different safety advantages. The primary benefit is the elimination of spilled liquid gasoline, which creates a persistent fire hazard. Propane vapor dissipates quickly if leaked. However, all pressurized fuel systems require proper handling, connections, and storage. Both are safe when used correctly according to the manufacturer’s instructions.

Q: Where can I buy the optional adapter for a larger propane tank?
A: The official Mercury adapter hose (Part Number 8M6005550) is available through authorized Mercury dealers, major online marine retailers, and marine parts stores. It’s a highly recommended accessory that fundamentally improves the motor’s utility.

Conclusion & Final Verdict

The Mercury 5hp propane outboard forces a simple but important decision: do you prioritize convenience and low maintenance or absolute lowest upfront cost and longest runtime between refuels?

If you fall into the first camp, this motor is a revelation. It solves the most persistent annoyances of small-boat ownership. It starts. It runs cleanly. It stores without fuss. It eliminates seasonal maintenance chores. For the sailor, the weekend angler with a jon boat, or anyone using a small tender, it represents a smarter, more enjoyable way to get on the water.

Final Verdict: The Mercury 5hp propane outboard is a brilliantly engineered, niche-perfect engine. It’s not the cheapest or the longest-running option per tank, but for its target audience—those who value simplicity, reliability, and cleanliness above all else—it is arguably the best small outboard on the market today.

Ready to experience hassle-free boating? Explore our full range of portable outboard options, including detailed guides on maintenance and selection, at https://hidea-outboardmotor.com/outboard-buying-guide.

Still have questions? The best next step is to consult with the experts at your local authorized Mercury dealership. They can provide hands-on advice and ensure it’s the right fit for your specific boat and needs.