​Boat Fuel: Do Boats Use the Same Gas as Cars?

Whether you already have a boat or are planning to get one, understanding marine gas is a must. You need the optimal marine fuel for the engine to ensure a reliable performance and optimal results while out there on the water.

Now, different brands or even makes will require different types of fuel. Just like in cars, using the wrong fuel can destroy the engine and give you many headaches. Most importantly, internal engine parts will be damaged, as well as the fuel system.

Most new boat owners simply ask upfront, whether they get their boats from dealers or purchase used boats. But then, it is still quite confusing, whether it comes to specific levels of ethanol, mixing fuel and oil, or even using classic diesel.

So, what is marine gas, and what do you need to know about it?

What is marine gas?

Marine gas – also referred to as marine fuel or even marine oil, despite being different – is a mix of different distillates. Distillates, on the other hand, are evaporated elements associated with crude oil. They are turned from gas into liquid.

Now, the process is similar to the manufacturing procedures associated with car fuel. From many points of view, marine gas is quite similar to diesel. However, it does not mean you can use classic diesel safely – the density is different. Plus, it has to be stored differently too.

Now, marine gas is available in more types, and different types of boat engines require different types of fuel. While knowing upfront what you need is a good idea, it pays off having a few clues about different types of fuels – quite handy if you ever feel confused.

REC 90 – Specs and uses

Gasoline with no ethanol in its composition is made at different levels. REC 90 is among the most popular ones, especially since it is very useful for small engines. Just like you may already know, it has no ethanol in its composition.

It is suitable for engines that could be damaged by ethanol. This fuel comes with one major advantage over gasoline rich in ethanol – it does not have the same corrosive capabilities. All these effects become history, so it is excellent for sensitive engines.

Once in, you should expect a top-notch performance, as well as an increased lifespan. While it may seem perfect, it is not. In fact, it comes with a few drawbacks as well. For instance, it is more expensive than most types of gasoline out there.

Then, it is rich in an additive that aims to make the exhaust cleaner – useful for the environment, indeed. But when mixed with ethanol rich fuels, it will cause some sort of gummy residue that can clog filters. Therefore, a thorough internal cleanup might be needed if you need to change the fuel. 

E10 – Common uses and benefits

So, what is marine gas? E10 is one of the most popular types out there. It is extremely common and also inexpensive when compared to other similar fuels. It is a safe option for any boat engine out there – you should still double-check upfront, though.

The code is self-explanatory – it has 10% ethanol in its composition. Compared to other fuel types, E10 is relatively new on the market and has just made its way into cars. The role of ethanol is quite easy to understand – reducing pollution.

Just like any other type of fuel, E10 is not perfect either. Make sure your boat can take this type of marine gas, or it could corrode fiberglass and plastic components in no time. It can also clog fuel lines if used incorrectly.

Ethanol goes through a separation phase that lets water into the fuel system, meaning corrosion is even more likely to occur. Ensure all the E10 is removed from the boat before long-term storage.

Once again, E10 is quite new, so some boats may have been manufactured before it came out. Performance issues are perfectly normal – you even risk ruining the engine if your boat cannot take this type of fuel. This is also why some boat owners use fuel additives. 

Ethanol free gasoline – Any worth?

REC 90 is one of the most popular types of ethanol free gasoline, but is it the only one? Definitely not. You do have some good options out there, and most of them are differentiated by the octane levels in the composition.

Some of the most popular choices include 87 and 92 octane levels. While these levels are quite common for many boats, never take it for granted – always make this decision with the owner’s manual in hand. Double check everything. 

E15 – The next level from E10

In terms of composition and effects, E10 and E15 are similar but not identical. Just as the name clearly states, E15 has much more ethanol in its composition – 15%. While much cheaper than E10, it is not a viable option for many boats, unless mentioned in the owner’s manual.

Why? Simple – the separation phase is even more intense. Therefore, internal corrosion is an even higher risk. At the same time, E15 pollution is quite harsh, so double check the laws in your area – even if your boat can take this type of fuel. 

Can you use diesel for boats?

What is marine gas? There are more explanations out there, and each of them depends on the characteristics and properties. Take classic diesel, for example. You might have asked yourself: Do boats use the same gas as cars? Sometimes, they do.

Classic diesel works with diesel outboard engines. Such models are quite rare these days. With all these, you may also find inboard engines that need diesel to run. This fuel comes with a few benefits that no one can overlook.

For example, it provides extra horsepower and torque. It sounds good, but you do not necessarily need these things to run your boat. This is why diesel is mostly used by large vessels, usually with commercial purposes.

Diesel is more expensive than other types of fuel for boats. But on the same note, it is about 10% more efficient, so it might be the more cost-effective option. Diesel engines also last longer, saving your money in maintenance.

Keep in mind that just because some engines can run with diesel, it does not mean that you should put diesel in them. Always check the owner’s manual to ensure you put the right fuel, even if its costs more or it is not that effective. 

Other types of marine gas explained

Some boat engines will require more than just fuel. For instance, small outboard engines and even the two stroke models without too much power will do with a mix of gas and oil. You will need to prepare this mix yourself.

Oil has a pretty simple purpose – just like in cars. Its role is to lubricate parts on the inside, so there would be less friction. This mix is not the type of DIY project, especially if you are not too experienced with boats.

First of all, the mix should be performed on particular engines and not all of them. Large and new engines have a separate lubrication system, so they do not necessarily need such oil and gas mixtures – forget about this trick.

Second, there is no perfect formula that works for every type of boat engine out there. Again, you would have to check the owner’s manual. Some of the most popular rations of gas and oil include 50:1 and 100:1.

Apart from these mixes, you may also find MGO (Marine Gas Oil) and MDO (Marine Diesel Oil) on the market – often advertised as designed for boat engines. These types are more common for large commercial boats, rather than small boats for recreational activities.

Experts would consider these fuels distillates. You are less likely to find them in basic stores – even specialized stores. Instead, they are more common around marinas – suitable for experienced users who know what they are doing. 

What is marine gas, and how to choose the best marine gas for your boat

Marine gas is a general name given to more types of fuels used for boats. Now, choosing the right fuel type is not just a matter of personal preferences. Instead, you need to ensure your boat can have the respective type. Here is everything you need to know and what to pay attention to. 

Grab the owner’s manual

The owner’s manual will give you all the information you need. If you get a used boat and the manual is no longer with it, you can probably order it online or perhaps find it in a digital format. You could ask a specialist for help, but the owner’s manual will most likely give you all the details.

Try to find the engine specifications in the manual. Follow both the fuel and oil specifications – if you get a new boat that is still under warranty, failing to follow these recommendations can void the warranty, leaving you to pay for repairs should any unexpected situations arise. 

Old engines versus new engines

These days, new engines can easily run with up to 10% ethanol content in the marine fuel. Most modern engines can take this fuel inboard, outboard or stern drive. You should, however, double-check the specifications upfront.

Things are different when it comes to the old boat. Even some old models can take this type of fuel, but back in the day, many engines were built and designed before ethanol was actually added to fuels. Therefore, you may need to stick to ethanol free fuel or diesel – just check the specifications. 

Boat size

Different engines have different needs, and they often depend on the boat’s size. The horsepower is just as important in the process. Take small boats, for example. They normally do with gasoline or different mixtures of oil and gas.

On the other hand, middle sized boats do with similar fuels, but they can often take diesel too. These rules typically apply to boats under 40 feet in size. Finally, large commercial boats will almost always do with diesel – after all, they require performance. 

What happens if you use the wrong fuel in a boat

According to Crown Oil, the wrong fuel in boats has similar effects to when you put the wrong gas in cars. Basically, the boat will still work for minutes or even hours, but everything may get clogged, and the engine will most likely fail.

Internal corrosion is probably the most common effect. Put some fuel with a high ethanol content into a very old boat, and the ethanol will corrode many of the internal components, leading to an obvious failure in no time. Internal components can also seize.

You should notice a difference straight away because the combustion will be severely affected. Engine bogs, stalling, and even an uneven idle should be some obvious signs. When smoke comes out of the engine compartment, you know it is about to fail.

Other signs of using the wrong fuel include:

• Fuel leaks behind the boat
• Water infiltrating into the engine
• Low RPMs, even when you accelerate
• Too much heat coming out of the engine 

What makes ethanol such a problematic compound

The truth is the ethanol in its composition tends to make the difference. It is probably the most important consideration when browsing through different types of fuels, for some good reasons.

The experts at Home Service Oil Company agree that as a general rule of thumb, you should try to avoid ethanol. Even if you have a relatively new boat and it can take ethanol rich fuels, you should try to avoid it if you can – especially if the content is higher than 10%.

Ethanol draws water in, as well as moisture. Such things should never reach the fuel system. The so called phase separation is behind this procedure. As more and more water is drawn in, the performance is seriously affected. Corrosion occurs, and internal components are affected.

If you need to use ethanol rich fuel, there are a few things most experts do to prevent the effects of phase separation. For instance, you could install a filter between the engine and tank, only to keep water away. You can also use a fuel stabilizer, especially when the boat is not in use for long periods of time. 

Do boats use the same gas as cars?

From some points of view, they do. From other points of view, you should not just load a canister with fuel from the nearest gas station, then pour everything into your boat. There are more considerations in the process.

If your boat can take ethanol rich fuels, you can use what you can find in regular gas stations – E10. It is the exact same type of fuel and can be easily used in more vehicles. Ethanol free gasoline is also acceptable, yet you are less likely to find it in gas stations.

It is important to know that E10 is the maximum recommendation in terms of ethanol concentration. Fuels with a higher ethanol content can affect the engine. For example, stay away from E15, unless specifically recommended by a manufacturer – less likely.

The answer can also go in a negative direction if you have a small outboard engine or perhaps a two stroke engine. These boats will normally need a mix of oil and gasoline. You need to know the proportions.

All in all, no matter what others say or recommend, the owner’s manual is your main source of information. That is how you know what fuel is alright for your boat. Sure, you can often use alternatives, but ideally, you should stick to what the manufacturer recommends.

Pay attention to what you have at the pump, though. The wrong fuel – not a full tank, but just a pinch – can seriously affect the performance and lead to damage. All these things can be avoided with a bit of attention. Finally, if a type of fuel is not clearly labeled, simply avoid it.

Wrapping up

So, what is marine gas? Marine gas can go in more directions, and just like for other vehicles or engines, different designs require different types of gas. It is perfectly normal, though – no matter what others are using or recommend, always stick to the manufacturer’s recommendations. Each engine has its specifications. Use the wrong fuel, and you will ruin the engine. Sure, some alternatives may work, but you want a full-on 100% performance, hence the necessity of using the right thing. If in doubt, simply get in touch with the manufacturer or dealer.