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What Octane Is Marine Gas? (Marine Gas vs Premium Gas)

Marine gas usually has an octane level of 89 to 90 and is ethanol free, which is more than enough octane to power a boat. Using the right marine fuel in your boat’s engine, whether that be inboard, outboard, or sterndrive makes sure that your boat will perform well all season.

If you have any queries regarding the oil and fuel requirements for your boat’s engine, the owner’s manual should be your first port of call. It’s important to make sure you adhere to the fuel and oil specifications in the manual.

What Octane Is Marine Gas (Marine Gas vs Premium Gas)

Not only to keep your boat running smoothly, but also so you’re in compliance with the warranty requirements.

But is marine gas better than premium gas? What is the difference between them, and what’s the best choice for your boat? We answer those questions below, as well as tell you all you need to know about ethanol and fuel stabilizers. 

What Is Premium Gas?

The difference between premium gas and regular gas is that premium gas has a higher octane rating. Octane is a chemical component found in petroleum, and how much octane a fuel has will determine how effective it will be in higher compression engines. 

Lower octane fuels are available, but can cause ‘knocking’ when added to your boat or car. ‘Knocking’ is when the combination of fuel and air in the engine’s cylinder head doesn’t burn correctly. This causes the engine to make a rough, pinging noise when it’s running.

At worst, lower octane fuel can damage your engine completely. 

What Is Marine Gas?

It may surprise you that boats actually use the same gas as cars do! However, the big difference is how much you’ll pay for gas. The gas you’ll find at a gas station costs a lot less than the gas you’ll find at the marina because of supply and demand.

You can also use the same diesel you’d put in your car in your boat with a diesel engine too. 

But bigger boats like ships will use different fuels depending on the engine design and type. These could be HFO (Heavy Fuel Oil), IFO (Intermediate Fuel Oil), MDO (Marine Diesel Oil), or MGO (Marine Gas Oil).

These fuels are the heaviest commercial fuels you can obtain from crude oil, meaning they’re heavier than gasoline and naphtha. 

You can save a couple of cents if you fill up your small boat at a gas station instead of the marina, especially if you use a trailer to take your small boat to the marina. 

What Kind Of Gas Should You Use In Your Boat?

Personal boats: As we have mentioned above, smaller, personal boats use the same gasoline as your car. You can use 87 octane unleaded gas, 89 octane mid-grade gas, or 93 octane premium gas or diesel.

The most important thing to remember though is that the gasoline shouldn’t have any ethanol in it (we’ll discuss that more below).

Larger boats: Larger boats have more specific fuel types and have a totally different classification to smaller, personal boats, which we have mentioned above. Marine Gas Oil (MGO) is a combination of light cycle gas oil and aromatics, and sometimes contains waste products such as used motor oil.

Meanwhile, Marine Diesel Oil (MDO) is a type of diesel that is made of heavy fuel oil. This is a totally different type of diesel to the type you would use to power your car.

Is Ethanol Safe To Use To Fuel Your Boat?

Is Ethanol Safe To Use To Fuel Your Boat

There is some confusion about ethanol and whether it is safe to power your boat with it. Ethanol is tempting because it’s often cheaper than other types of fuel, but it’s recommended to not use ethanol if you can.

Ethanol can lead to a wide range of issues with your boat’s engine such as carbon deposits, moisture, and phase separation. 

However, if you have to use ethanol-based gasoline, try to go for E10. If you’re unsure, you can take a look at the pump in the marina to confirm that you’re filling up your boat with ethanol-free gasoline, especially because some states like Missouri are not legally required to label their gas as containing ethanol. 

What Are Fuel Stabilizers?

Fuel additives (or stabilizers) don’t have the best reputation, and are often compared to snake oil. But what is a fuel stabilizer?

You may have seen gasoline that is very dark, or you may have opened a gas can and noticed a strange smell. You may have even seen gasoline that just looks like varnish. All of these are the result of a chemical reaction that destabilized the fuel. Heat, light, and oxygen can all negatively affect your fuel. 

Still, fuel stabilizer can’t fix gasoline once the chemical reaction has happened. But what it can do is prevent it from being destabilized in the first place, especially when it’s left to float for an extended period of time.

What Are The Advantages Of Using Gas To Fuel Your Boat?

  • Gas is often less expensive than diesel.
  • Gas produces less smoke than other fuels such as diesel.
  • Combining ethanol like E10 with gasoline decreases smoke pollution.

What Are The Disadvantages Of Using Gas To Fuel Your Boat?

  • Keeping ethanol gas in the tank for an extended period of time can corrode the fuel lines and even the tank itself. 
  • It can be dangerous, as exhaust gases from gas engines contain carbon monoxide. 
  • E15 ethanol combined with gasoline causes more pollution. 
  • Gasoline motors do not produce the torque needed to run a bigger boat.

What Are The Advantages Of Using Fuel Oil In Big Ships?

  • Fuel oil is sometimes cheaper than gasoline.
  • Fuel oil produces 6.3 MMBTU/Gallon energy per gallon, while gasoline only produces 5.25 MMBTU/Gallon per gallon.
  • As gasoline can be a fire hazard, fuel oil is safer to store than gasoline.
  • Big ship engines turn at a significantly lower RPM and are not built to run on gasoline.
  • Fuel oil is thick and heavy, which not only powers the ship better, but it’s also more compact and leaves more room for cargo.

What Are The Disadvantages Of Using Fuel Oil In Big Ships?

  • Big ship engines are more expensive to get repaired, and fuel oil is more expensive to replace.
  • The thickness of the fuel makes it messier.
  • While fuel oil is less of a fire hazard than regular gasoline it does have its dangers. Bunker fuel is a low quality fuel that can cause particular harm to humans, such as serious illness or even death.

Final Thoughts

To sum up, boats, and smaller boats in particular, are powered by the same gasoline as cars, but it costs you a lot more to refuel at a marina than it would at a gas station. This is due to the supply and demand at the marina, which causes the marina to increase its prices.

While you can also use the same diesel to power your diesel engine boat as you would your car, gasoline is better for a smaller boat as it’s powerful while producing fewer emissions than other types of fuel.

However, this is not the case for bigger boats and ships, as they use different fuels and their own specific kinds of gas and diesel such as IFO, HFO, MGO, and MDO. These are heavier commercial fuels when compared to gas, and are obtained from crude oil.

Ships use fuel oils such as HFO and IFO because it is safer to use this type of fuel than the gas you’d use to fill up your car or smaller boats. All marine fuels, except for LNG, are legally required to have a flash point greater than 60C.

Petrol vapor is thicker than air, and any leaks would form in the lower parts of the ship. One spark could cause the engine room and the boat to explode.

But fueling your boat isn’t just about selecting the cheapest fuel and hoping for the best, you have to consider what the optimal fuel for your engine would be and what your engine requires.

You should always check your owner’s manual for the exact oil specification, but most manufacturers will require you to power boats with a four-stroke engine with oil that meets the FC-W certification.

You can check whether oil has this certification by looking for an FC-W symbol on the label. Oil that is FC-W certified protects from rust, which engine oils for cars cannot. It also imposes an increased minimum viscosity level.

This means that FC-W oil will not thin out like automotive oil with a similar viscosity when exposed to the same temperatures and RPM conditions. Meanwhile, Two-stroke outboards require oil that meets the TC-W standard.

So while you can use the same gasoline you would use to fuel your car to also fuel your boat, you should always consult with your owner’s manual in order to make sure you’re using a fuel that won’t damage your boat over time.

Premium oil isn’t better than marine gas either, as it simply just has a higher octane level.

Lucas Jones