Ameer Randolph
Installing an inline fuel filter on an outboard engine can help to protect the engine by trapping dirt and separating water from the fuel. While some sources recommend against using inline fuel filters, especially on Mercury outboards, others suggest that they can be beneficial, especially when dealing with ethanol in the fuel. It's important to consider the specific engine design and follow manufacturer recommendations when deciding whether to install an inline fuel filter. Additionally, the placement of the filter and the type of filter chosen can impact its effectiveness and potential drawbacks, such as fuel starvation due to vacuum issues.
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What You'll Learn
Fuel filter placement
When installing an inline fuel filter, it is recommended to place it after the fuel pump. This is because the vacuum produced by outboard pumps can be weak, and placing the filter before the pump can cause fuel starvation. It is also important to note that not all outboards have a fuel/water separator filter, but it is highly recommended to install one to protect your engine from water intrusion.
For Yamaha outboards, the primary fuel filter is usually placed on the front, side, or back of the powerhead. It is made of transparent plastic and contains a small water trap at the bottom. An in-line filter can be placed between the primary fuel pump and the Vapor Separator Tank (VST) or between the VST and the outboard's fuel rail.
For Mercury outboards, it is recommended to refer to the specific replacement process outlined in the outboard motor user manual. It is important to choose a filter designed specifically for your engine by its manufacturer, such as genuine OEM filters from Mercury, Evinrude, or Volvo.
Additionally, the fuel filter placement can depend on the engine type. For example, if your engine has a carb, a small inline mesh filter should be sufficient to trap any particles. However, if your engine has an EFI system, it is beneficial to have a cleaner fuel supply to prevent wear on the injectors.
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Fuel line size
For smaller outboard engines, a 5/16" fuel line is typically suitable. This size is considered the standard for smaller engines and can be used for up to a 115 HP outboard engine. The 5/16" fuel line is perfect for little kicker motors and sailboat outboard engines as it easily fits into smaller rigging tubes while still providing the proper amount of fuel to the engine.
However, for larger outboard engines above 115 HP, it is recommended to use a 3/8" fuel line. This is because larger outboards require more fuel to run at higher RPMs, and a smaller fuel line can cause strain on the fuel pump, leading to premature failure or damage to the engine.
It is worth noting that some sources suggest that a 5/16" fuel line may be marginally too small and recommend using a 3/8" fuel line for improved performance. Additionally, the type of fuel line material should be considered, with reinforced neoprene being one recommended option.
When selecting a fuel line size, it is important to understand the engine's flow rates and pressure drops to ensure proper performance. It is also crucial to consider the fittings and connections to prevent leaks and ensure a secure fuel supply to the engine.
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Fuel filter type
Fuel filters are critical for the longevity of your outboard motor. It is important to choose a filter designed specifically for your engine by its manufacturer. There are several types of fuel filters available for outboard motors. The type of fuel filter you need will depend on the make and model of your outboard motor, as well as the specific requirements of your engine.
Some Yamaha 4-stroke outboard engines, for example, use several different fuel filters to prevent debris and water from entering the engine. The first filter in the fuel line is typically a 10-micron fuel-water separating filter, which needs to be changed every 50 hours of engine use. Yamaha recommends carrying a spare filter onboard in case of a bad tank of gas that overwhelms the original filter.
Mercury Marine also offers a range of fuel filters for their outboard motors. They recommend inspecting and changing the fuel filter every 100-300 hours of use, or more frequently depending on operating conditions. Mercury Marine dealers offer genuine OEM fuel filters that are designed specifically for their engines.
It is important to note that not all fuel filters are compatible with all engines. For example, one user reported that they installed a Racor 60 GPH fuel filter/water separator between the tank and the primer bulb on their V6 Merc, instead of the screen-type filter. Another user with a Mercury outboard motor cautioned against using an inline filter before the fuel pump, as the vacuum produced by the typical OB pump can cause fuel starvation. Instead, they recommended installing the filter after the fuel pump.
When choosing a fuel filter for your outboard motor, it is important to consider the specific requirements of your engine and to follow the recommendations of the manufacturer. Additionally, it is crucial to perform regular maintenance and inspections of your fuel filter to ensure optimal performance and prolong the life of your outboard motor.
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Fuel filter orientation
It is recommended to place the inline fuel filter after the fuel pump. This is because the vacuum produced by outboard fuel pumps may not be sufficient to draw fuel through the filter, especially if the fuel is of low quality. Installing the filter before the pump can cause fuel starvation and rough idling.
Some manufacturers, such as Mercury, recommend against using an inline fuel filter in conjunction with a water-separating filter. They state that using multiple filters can damage the engine. Instead, they suggest using a fuel/water separator, which serves as both a filter and a water separator. This is a relatively new addition to boating due to the use of ethanol in fuel.
It is also important to consider the type of filter used. Cardboard filters should be avoided in boats as ethanol can degrade them, leading to potential clogging of fuel jets. A mesh screen filter or a fuel/water separator is recommended instead.
Additionally, the size of the micron filter matters. Yamaha recommends a 10-micron filter, which is considered very fine, while Mercury cautions against using more filters as they can damage the engine.
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Fuel type
Most outboard motors are designed to run on E10 gasoline, which contains up to 10% ethanol. However, it is important to check the owner's manual for specific recommendations, as some outboard motors may specify a different type of fuel. Using a higher ethanol blend, such as E15, can damage the engine and cause excessive emissions. Therefore, it is generally recommended to use ethanol-free fuel or E10 where possible.
Another consideration is the octane rating of the gasoline. Outboard motors typically require regular 87-octane gasoline, and using premium gasoline with a higher octane rating is usually unnecessary and will not provide any additional benefits. However, in situations where the quality of the gasoline is uncertain, upgrading to premium gasoline can be a safer option.
Some older two-stroke outboard motors may require a fuel-oil mix, which can be challenging to get right. These motors usually have a separate tank for two-stroke oil, and it is important to follow the manufacturer's recommendations for the correct oil-to-gasoline ratio, which is typically 50:1 for newer motors and 25:1 for older motors. Using the wrong ratio can lead to serious issues, including internal damage to the motor.
Additionally, the use of fuel additives and conditioners can be beneficial, especially when using lower-quality gasoline. Fuel stabilizers can help protect the motor from sour gas during extended storage, while fuel anti-freeze can address water in the fuel due to condensation. However, excessive use of anti-freeze can wash off the oil from cylinder walls in two-stroke engines.
Finally, it is worth noting that some outboard motors may be diesel-powered, particularly in larger boats. Diesel motors tend to be more powerful and fuel-efficient, making them a popular choice for long-distance boating and heavy loads. However, they also tend to be more expensive and louder than their gasoline counterparts.
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Frequently asked questions
It is recommended to use a 10-micron fuel filter, as these are very fine and can help to separate water from the fuel. However, some people suggest using a water separator instead of or in addition to a fuel filter, as fuel filters do not trap water.
It is recommended to install the fuel filter after the fuel pump, as installing it before can cause fuel starvation due to the low vacuum produced by outboard pumps.
To get rid of air bubbles, tilt the filter so that the outlet is at the top, then pump the priming bulb until the air is displaced by fuel.
