Best Gas for 4-Stroke Outboard

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Every 4-stroke outboard owners’ are concerned about the performance of the engine.

The types of gas you fuel your boat with, is are what determines the performance of the engine and its durability. Sometimes, it challenges to know the best gas for your 4-stroke outboard. 

When you fuel it with the wrong gas, it might damage the engine, and make it perform slowly. You wouldn’t want to damage your boat engine. Because you might not be pleased with the cost to repair it.

Also, the speed of a 4-stroke outboard is dependent on the types of fuel it uses. Sometimes, the delay in the speed might be fueling it with the wrong gas.

There are many other problems associated with using the wrong gas for your 4-stroke outboard.

This article, it’s written to show you the best gas for your 4-stroke outboard, how to use it, and get a better result.

How Do I know The Right Gas For My Boat?

Every boat doesn’t run on the same gas. The types of fuel your boat uses depend on the capacity of the engine.

Check the owner’s manual to know the types of gas your 4-stroke outboard motors run on. Sometimes is close to the fuel gauge or inside the fuel cap cover. 

Another way to check for it is online. You can get the information online. Use the boat model and engine number to check online.

Basically, ethanol or octane should either be in the fuel of your 4-stroke outboard motor. Any of these two solvents will make the boat engine perform optimally.

Now that you know the gas to use, let us take a look at what ethanol and octane stand for in fueling your 4-stroke outboard motor.

Why Gasoline With Octane?

Octane is one of the solvents to run a boat. It helps the efficiency of the engine and increases its durability.

Octane rating is recommended for new drivers that don’t know anything about engine knock. Because it helps to avoid engine knock.

Octane rating is what measures the capacity of a fuel’s ability to avoid knock. What causes engine knock is when fuel ignites in the engine cylinder before the actual time it is supposed to have.

Octane sells in different grades at the gasoline stations. These grades are what determine the performance of 4-stroke outboard motor performance. The octane grade is:

  • Octane grade 87  (regular)
  • Octane grade 89 (mid-grade)
  • Octane grade 91-93 (premium)

According to the research carried out by American Petroleum Institute, Octane number is the measurement of fuel resistance to engine knock. 

Engine knock here, simply means an abnormal performance or combustion due to using gasoline that has a low octane number. 

The performance of octane is based on the grade. The higher the octane number, the more resistance of the gasoline mixture not to knock the engine.

When you use a higher octane number, it enables higher compression ratios, and turbocharging, and reduces speeding. 

Also, the higher octane in gasoline the better it enhances engine performance. 

However, your boat will not perform excellently, when you use gasoline that has a higher octane number rather than the recommended number by the manufacturer.

The size of your boat engine is what determines the number of octanes you fuel it with. 

If your boat engine has a higher compression ratio or uses supercharging to take air into the engine, then you need to fuel it with gasoline that has a higher octane number.  

The higher the pressure in the cylinder, the more the engine extracts mechanical energy from a given fuel mixture. 

Though, the engine requires higher octane fuel to keep the mixture from pre-detonate. Gasoline with a higher octane number will improve the performance and fuel economy of the engine.


Before the discovery of octane, automotive manufacturers were searching for chemical substances to reduce the engine knock. 

The search started in the early 20th century but in 1921 the discovery of lead came to light.

Tetraethyl lead (known as a lead) was discovered. This substance made available octane in the gasoline — which is used to prevent engine knock. 

Likewise, the discovery of alcohols (such as ethanol) and hydrocarbons (known as benzene) came into use as well. Benzene and ethanol were also used as octane.

The choice of which one to use was now dependent on the cost of production. Users shifted attention to the least cost. Then, the least cost was ethanol.

Until the 1970s, when the United State Environmental Protection Agency (EPA) began to phase it out because of health-related issues, it remained the leading gasoline in the U.S.

Leaded Gasoline — Health Concerns

Over the years lead became the most used gasoline in the market. Boat owners are additive to it. 

Then, health issues were raised because of its excess usage. Lead remains the most used gasoline for boats back in the old days.

Cases of death were recorded, which were traced to gasoline that contained lead. Over 10 refinery workers in both New Jersey and Ohio were suspected to have died of lead poisoning, according to the Environmental And Energy Study Institute.

Because of the death, the production of leaded gasoline was suspended to envisage the feature occurrence and to ascertain the cause of the death.

After much investigation, the panel that was set up found out that there was sufficient evidence about the alleged cause of the refinery’s worker death. After the report, the production of leaded gasoline started again.

Even though they couldn’t find anything but issue a warning, which says a continuing exposure to lead might cause serious degenerative disease. Also, the disease takes time to manifest. 

Immediately after the warning, the Surgeon General issued conditions that will make them start production. The refining industry met its conditions and started production.

Another extensive health research was done in the 1960s that had a negative report on the health implication; for children it caused low-level and ambient exposures to lead. 

Some of the health-related issues discovered in children are anemia, behavioral disorders, and low IQ.

In adults, the lead exposure is related to hypertension, and cardiovascular disease. Before it was phased out, the total amount of gasoline used annually was 100,000 tons.


A mixture of ethanol in the gasoline helps to prevent filter blockage that might damage the engine. It also helps to diminish pollution in an engine.

Ethanol is an oxygenate agent that reduces hydrocarbon emissions. It’s one of the best cleansing agents. It’s highly solvent and antifreeze. 

Ethanol blended with fuel is not healthy or safe to drink. It has the capacity to break down solid materials including rubber seals, plastic, steel, aluminum, and fiberglass.

Gas blend ethanol helps to dissolve corrosive matter/rust and varnish that would block the fuel from filters.

Types of Ethanol 

There are three main types of ethanol you can easily find in gasoline. Which are:

  • E0 (0% Ethanol with 100% unleaded gasoline )
  • E10 (10% Ethanol with 90% unleaded gasoline )
  • E15 (15% Ethanol with 85% unleaded gasoline )

The “E” stands for ethanol while the number attached to the “E” stands for the percentage of ethanol present in unleaded gas.

Among these types of ethanol, the most common among all is E10, which means the presence of ethanol is 10% while gasoline is 90%.

It’s recommended you follow the fueling instruction of your boat engine manufacturer so that you can probably fuel it with the right percentage of ethanol.

If the manufacturer of your boat engine instructs you to fill it with E10%,  then don’t over or under fuel the engine — it might affect the performance of the engine. 

One of the functions of ethanol is to ensure that no-clog substance blocks the fuel filter from sending the right gas to the engine.

Irrespective of the amount of water the ethanol absorbs, the engine will still function normally. 

When water comes in contact with gasoline blended with ethanol, the ethanol separates the water and the fuel in a different layer inside the tank. 

Water does not stop the gasoline from its function because the ethanol presence performs a distinct separation in the tank.

The separation goes like this: The upper layer is the gasoline with a reduced octane, while the lower layer is the corrosive substance of a mixture of water and ethanol. 

The 4-stroke outboard motor engine doesn’t function with gasoline with water. Though the presence of ethanol separates the water from the gasoline — the distinct separation enables the engine to use the gas. 

The filter that takes gas to the engine starts from the top solvent. This process doesn’t allow water into the engine.

Can I Use E15 Instead of E10 for Ethanol?

If the specification for your engine is E10, then don’t use E15. stick to the required amount of ethanol recommended for your engine boat.

So long the specification is not E15 don’t use it, because it might cause the engine to develop a mechanical fault. You might end up losing your boat engine completely.

The higher the number of ethanol, the more concentrated it’s inside the gasoline. There are some engines that don’t require a high concentration of ethanol.

High concentrated ethanol has the power to dissolve fiberglass fuel tanks. It does affect the fuel filter and the carburetors.

However, ethanol is the perfect cleaner, especially gasoline with E10. High concentrated ethanol like E15 has the capacity to dissolve polymers. This type of ethanol has the power to stop your boat’s engine.

The capacity of ethanol to attract water is scientifically called hygroscopic. Ethanol absorbs and attracts condensation. 

This process might stop your 4 stroke outboard engine from functioning. Using the right ethanol to run your boat engine makes it more efficient and durable. 

Is 4 stroke outboard motor reliable.

No one wants to buy or invest in an outboard motor that will not serve the purpose.

Durability and reliability are major features people look out for in any outboard motor. There is nothing worse than stepping into your boat to move and it refuses to start. 

The disappointment isn’t worth experiencing. That’s many will rather go for durable, reliable, and consistent outboard motors like 4-stroke outboard motors.

However, how reliable and durable your 4-stroke outboard motor is is a function of the types of gas you’re using.

The 4-stroke outboard is consistent, dependable, and built to power any adventure. Most people prefer the 4 stroke outboard motor because they’re worry-free for boating.

The 4-stroke outboard is not just durable but lighter and moves faster. It has gained popularity based on its speed level, low sound, fuel mileage, and low emissions.

These features make many who love boating prefer the 4-stroke outboard motor.

Why 4 Stroke Outboard is Prefer to 2 Stroke Outboard Engine

The 4-stroke outboard engine is more efficient compared to the 2-stroke outboard motors. 

This is because at every 4 strokes fuel is consumed once — unlike the 2 stroke outboard that consumes fuel at every 2 strokes.

4-stroke outboard engines are heavier than the 2-stroke outboard engine. At the upper level, 2 stroke has more torque while 4 stroke has more torque at the lower level. This makes the 4 stroke engine quieter than the 2 strokes outboard engine.

Also, the 2 strokes are easily worn out because they function at the upper level while the 4 strokes are more durable.

The 2-stroke outboard engine requires mixing of oil and fuel, while the 4-stroke outboard requires direct filling without any further mixing.


The best gas for your outboard motor is the one that contains octane or ethanol. These two elements help your 4-stroke engine to perform excellently.

Most importantly, fill your boat with the exact percentage of lead. Don’t go for the lower one or the higher one.

If there is any need for you to make changes, then contact the manufacturer for better instruction.

The right quantity of ethanol will make your boat engines to be more powerful and fuel-efficient engines.

Not just that it will make your outdoor motor engine last long and move smoothly. The best gas for your 4-stroke outboard motor is the gasoline that contains octane or ethanol.

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