Boat Fuel Basics: Understanding Gas Types For Marine Engines

The type of gas a boat takes depends on the type of engine it has. Most recreational boats have engines that use the same type of fuel. However, if your boat has a 2-stroke outboard engine, you'll likely need to use a mixture of gas and oil. Newer boats are likely to have engines that do not require oil mixed into the gas, such as 4-stroke engines, which get their lubrication from oil in the crankcase. It's important to refer to the owner's manual to determine the specific fuel requirements for your boat's engine. Additionally, it is recommended to avoid using fuel with more than 10% ethanol, as it can cause corrosion and damage to the engine.

Gasoline vs diesel

When it comes to choosing between gasoline and diesel for your boat, there are several factors to consider. Here is a detailed comparison to help you make an informed decision:

Performance and Efficiency:

• Diesel engines offer increased torque and horsepower compared to gasoline engines of similar physical dimensions, especially for larger, heavier boats.
• Diesel engines are generally more fuel-efficient than gasoline engines, with up to 10% better efficiency.
• Gasoline engines are more common in pleasure craft and smaller boats due to their lower cost and wider availability.

Cost and Maintenance:

• Diesel engines typically have a higher upfront purchase price and higher maintenance and repair costs compared to gasoline engines.
• Diesel engines may have longer life expectancies than gasoline engines, but modern gasoline engines have improved in reliability and performance.
• The higher cost of diesel engines may not be offset by fuel savings unless the boat is used extensively or for long trips, as it would take decades to recoup the initial investment.

Safety and Environmental Considerations:

• Diesel engines have a reputation for being safer than gasoline engines due to a lower risk of explosions, but modern gasoline engines are also very safe, and the risk of explosions is rare.
• Diesel exhaust produces less carbon monoxide (CO) than gasoline exhaust but generates sulphur dioxide, which can cause nausea.
• Gasoline with ethanol blends (E10 or E15) may cause corrosion and damage to older gasoline engines and fiberglass fuel tanks. Ethanol-free gasoline (E0) is recommended for older boats.

Size and Weight:

• Diesel engines are heavier and bulkier than gasoline engines, which can impact the speed and manoeuvrability of smaller boats.
• For larger boats weighing around 16,000 to 18,000 pounds, diesel engines may be the only feasible option due to their torque and power advantages.

In summary, gasoline is often the more economical and accessible choice for smaller boats, while diesel engines offer advantages in terms of torque, horsepower, and fuel efficiency for larger vessels. However, the higher upfront and maintenance costs of diesel engines may outweigh the potential fuel savings unless the boat is used extensively. Ultimately, the decision between gasoline and diesel depends on the specific needs, budget, and intended usage of the boat.

Ethanol-free gasoline

However, ethanol-free fuel is more expensive than E10 or other types of gasoline. It also uses the octane enhancer additive methyl tert-butyl ether (MTBE) to produce a cleaner exhaust for the environment. If you combine MTBE with ethanol from other fuel types, a gummy residue may cause clogged fuel filters and performance issues. Therefore, it is essential not to mix ethanol-free gasoline with other types of gasoline.

If you want to switch from ethanol-free gasoline to another type of fuel, it may require a thorough cleaning of all fuel tanks and lines to ensure optimal performance.

Ethanol is a powerful solvent that can dissolve fiberglass fuel tanks, as well as react with fuel filters and carburetors. It is also hygroscopic, which means it attracts water, which can cause a boat engine to stop working.

Mixing oil with fuel

The type of gas that a boat takes depends on the type of engine it has. Most boats use gasoline, which is the same type of fuel used by cars. However, diesel-powered boats are also common, especially for larger boats weighing around 18,000 pounds.

Now, if you have a 4-stroke gasoline engine, non-ethanol gas is perfect. If it is a 2-stroke engine, which is common with outboard engines, then non-ethanol fuel is also fine but make sure you mix it with 2-stroke oil. The oil is used to lubricate the moving parts of the engine.

• Only mix oil into your fuel if specified by the engine manufacturer. Most larger, modern boat engines have their own lubrication system separate from the fuel system.
• Use a special type of oil for boat engines. This oil is required to achieve the proper oil-to-gas ratio.
• Refer to your owner's manual to find the correct oil-to-gas ratio for your engine. Common mixing ratios (gas:oil) include 25:1, 50:1, and 100:1.
• For a 50:1 gas-to-oil ratio, you will need to use 2.6 fluid ounces of oil per gallon of gas added to your fuel tank.
• You can pre-mix your gasoline and oil in a separate container before filling up your boat's fuel tank. This can help ensure a proper mix and avoid an imbalance.
• Sloshing the fuel tank around during transportation to the boating facility can also help mix the oil and gas.
• It is generally recommended to add the oil first and then the gas. This ensures that you do not fill the tank too full and leaves room for the required amount of oil.
• Do not overfill your fuel tank. Leave some space for the oil to be added.
• If you have a built-in tank, you may want to premix the oil and gas in a gas can first to ensure a proper mix.
• If you are using a portable tank, you can shake the tank to ensure the oil and gas are mixed well.

Fuel efficiency

Engine Specifications:

The type of engine your boat uses is crucial when choosing marine gas. Refer to your boat engine's owner's manual for the recommended fuel type and octane rating. Using the wrong fuel can lead to reduced performance and engine damage. For example, smaller recreational boats like pontoons and speed boats typically use gasoline, while larger commercial boats over 40 feet will usually have diesel engines.

Using high-quality marine gas can improve fuel efficiency and performance, resulting in a smoother ride and better acceleration. Diesel engines, for instance, are generally more fuel-efficient than gasoline engines, offering increased torque and horsepower. However, they are also more expensive.

Environmental Considerations:

When choosing marine gas, consider the emissions of the fuel and ensure it meets Environmental Protection Agency (EPA) standards. Using fuel with lower emissions can reduce your boat's environmental impact. For instance, ethanol-blended fuel, a mix of gasoline and ethanol, is becoming more popular due to its environmental benefits, but it may not be suitable for all boats.

Two-Stroke vs. Four-Stroke Engines:

Two-stroke engines are simpler and lighter than four-stroke engines but are less fuel-efficient and emit more pollutants. Four-stroke engines are more fuel-efficient and emit fewer pollutants but are more complex and heavier. Two-stroke engines require a specific oil-fuel mixture, while four-stroke engines use gasoline only.

Fuel Choices:

The choice between ethanol-free gasoline, oil and gas mixtures, and marine diesel or gas oil depends on your boat motor. Ethanol-free gasoline offers the best performance and lifespan for your boat's engine but is more expensive. Oil and gas mixtures are required for smaller outboard and 2-stroke lower-horsepower models to lubricate the engine's internal moving parts. Marine diesel oil (MDO) and marine gas oil (MGO) are used in large commercial vessels and are not typically found at marinas.

Safe Fueling Practices:

Always follow safe fueling practices to protect your engine and yourself. Know the exact fuel your vessel needs, ensure you're pumping it into the right tank, and prevent overfilling. Keep passengers off the boat while fueling, and perform a "sniff test" after fueling to check for any fuel leaks.

Fuel safety

Before fuelling your boat, it is important to take several safety precautions to prevent harm to yourself, your passengers, and the environment.

Before fuelling:

• Securely dock your boat: Docking your boat properly will help to keep it stable while fuelling.
• Have passengers disembark: Asking passengers to step off the boat will also help keep the vessel stable and minimise the risk of spills and the release of harmful fumes.
• Prevent explosions: Ensure that no one nearby is smoking or engaging in any activities involving flames. Extinguish all open flames, such as the galley stove, and turn off anything that could cause a spark, including the engine, fans, and other electrical equipment.
• Check your equipment: Inspect your fuel lines, connections, and fuel vents to ensure they are in good condition. Make sure that the air vents and valves to the gas tank are open.
• Close all openings: Close all windows, ports, doors, hatches, and any other openings to prevent fumes from entering the boat.
• Keep a fire extinguisher close: Even when following all necessary safety procedures, it is a good idea to keep a fire extinguisher nearby in case of an emergency.

During fuelling:

• Fill portable tanks on the dock: Keep portable fuel tanks away from your boat to prevent spills and fumes from coming into contact with electrical equipment.
• Prevent spills and fumes: Hold the nozzle firmly against the fill pipe opening to ground it against static buildup. Use an absorbent pad to catch any drips or spills.
• Do not overfill: Do not fill your tank above 90% to allow for gas expansion and prevent accidental discharge through the fuel vent.

After fuelling:

• Keep the gas cap tight: Tightly screw the gas cap back on to prevent spills and reduce the possibility of debris getting into the tank.
• Allow air to circulate: Reopen windows, doors, and other openings to allow air to circulate through the vessel.
• Check for fumes: Wait for the scent of gasoline to dissipate before turning on the engine. If you have an inboard gasoline engine, turn the blower on for at least four minutes before starting the boat to remove any remaining fumes.
• Store portable tanks carefully: If using portable tanks, store them in a well-ventilated area away from the engine and electrical equipment.

Additional tips:

• Fuel during the day: Fuelling during the day is safer than at night, as it eliminates the need for additional lighting, which can pose a risk near gasoline.
• Take action in case of a spill: If a spill occurs, stop the source immediately. Use oil-absorbent pads to clean up any gas that has spilled onto hard surfaces. If it has entered the water, notify your marina, as they may have additional information or agencies to contact.
• Follow environmental laws: It is illegal to leave an oil or fuel spill unreported if it is large enough to leave a sheen on the water. It is also illegal to disperse a spill by adding additional chemicals to the water.
• Conserve fuel: Keep your engine well-maintained, perform regular oil analyses, and keep up with general boat maintenance and cleanliness to reduce fuel consumption.

Frequently asked questions