What Fuel and Oil Does Your Boat Need?

sailing boat

Like any motor vehicle, boats require fuel and oil to operate correctly. But you may not realize that your choices of oil and fuel can have a massive effect on the performance and longevity of your vessel. What are the different types of fuel and oil that are available for boats? And how can you choose the right fuel and oil for your vessel?

The Role of Your Motor

First, you should know that the type of motor in your boat will dictate what type of fuel and oil you use. If you have a pontoon or a small personal boat, you’ll probably need either regular petrol or a blend of petrol and oil. But if you’re operating a large boat, like a commercial vessel, you may need diesel. Diesel fuel tends to result in louder engines, and it’s more expensive – but it also tends to operate more efficiently.

Ethanol Content

Modern petrol is often produced with ethanol content. Ethanol is a type of alcohol introduced to fuel to reduce pollution created by engines. It also tends to be less expensive than other types of petrol. Fuel is separated into categories based on how much ethanol content it has.

For example, E10 is fuel that has ethanol content of 10 percent. E15 is fuel that has ethanol content of 15 percent.

While ethanol can be good for the environment when included in fuel, there’s some controversy over how it’s used in boats. The reality is ethanol can degrade your boat in several ways.

For example:

  • Corrosion of certain materials. Ethanol is a solvent that has the potential to corrode certain types of materials, such as fiberglass and rubber. This can deal superficial damage to your boat in the event of a spill, but more importantly, it could loosen debris in your fuel tank, ultimately leading to your fuel lines being clogged.
  • Engine damage. High-ethanol petrol can cause degradation and damage to some types of engines, especially if used over a long period of time.
  • Water separation. Ethanol attracts water on a chemical level. A small amount of absorbed water won’t have much of an impact, but if the water becomes excessive, it could settle outside of the fuel, or on the bottom of your fuel tank, rendering your engine unusable.
  • Negation of environmental benefits. One study by The Department of Energy’s National Renewable Energy Laboratory found that the use of E15 petrol can cause boats to exceed EPA emission standards. If the environmental benefits of ethanol are negated, there’s even less of a reason to include it in your fuel choices.

For the most part, modern outboard, sterndrive, and inboard petrol engines have been created to withstand the use of E10 petrol. However, using a blend with higher concentrations of ethanol (e.g., E15) is not recommended – and could void the warranty of your motor.

If your boat or your motor is more than a decade old, the engine likely wasn’t built to tolerate the presence of ethanol. Introducing any ethanol-containing fuel into one of these machines could cause it to be damaged or completely break down.

Because of these constraints, many boat owners choose to fill their boats with ethanol-free petrol altogether whenever they can find it. Ethanol-free petrol is often more expensive and harder to find, so it’s not always an option.

Switching to Ethanol

If you’ve been using ethanol-free petrol as the primary fuel source for your boat, and you want to switch to ethanol for any reason, there are some things you’ll want to do first:

  • Identify and understand the engine you’re using. Make sure your engine is new enough that it can tolerate ethanol fuel.
  • Remove any water and debris from your fuel tank. If there’s any water or excessive moisture in your fuel tank, you’ll want to completely dry it. You may need to use a cleaning product to clean out your tank completely.
  • Introduce E10 to your fuel tank. With only a little bit of water remaining, E10 fuel can absorb whatever water is left and still operate as it should.

The Impact of Octane

Different types of fuel also come with different octane ratings. The standard octane for petrol is 87, and most boats on the water will tolerate this octane rating just fine. However, higher octane-rated petrol delivers more powerful performance – and are recommended for certain types of performance boats.

Choosing the Best Oil

Different engines will have different requirements, but most four-stroke engines will need motor oil that meet FC-W certification requirements. FC-W certified oil will offer rust protection and a higher minimum viscosity, reducing the role of thinning. If you have a two-stroke engine, you’ll likely need oil meeting the TC-W standard.

Additional Tips

These additional tips can help you use fuel and oil properly:

  • Carry a spare filter element. Boats typically come equipped with a water-separating fuel filter that helps to keep debris out of the engine. It’s a good idea to keep a spare on board to ensure it continues operating as it should.
  • Use fuel stabilizer. Fuel stabilizer designed for marine engines will reduce the likelihood of phase separation and limit the role of oxidation.
  • Use your fuel quickly. Fuel can begin to oxidize in just 15 days. If you’re not going to use your boat for a while, don’t fill up the engine.
  • Inspect and maintain your boat regularly. If you want to keep your boat and its motor in good condition, it’s important to inspect and maintain your boat regularly – and take care of possible issues proactively.

The Bottom Line

It’s good to know how ethanol and octane levels impact the use of fuel, but if you want to use the correct fuel and oil confidently, you’ll need to consult your owner’s manual. Get a specific recommendation from your manufacturer, and follow the guidelines as outlined.

If you’re looking for a new boat that can tolerate ethanol-containing fuel much better, or if you’re just looking to see what’s available, be sure to browse TheYachtMarket’s selection of new and used boats for sale today!

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