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Fuel Senders for Boats - Resources & Information

Fuel senders are important in boats and outboard engines because they allow the operator to monitor the level of fuel in the fuel tank. Maintaining and replacing the fuel sender periodically ensures optimal performance and control of your vessel on the water. 

PartsVu offers a complete selection of Fuel Senders from OEM manufacturers and trusted aftermarket suppliers. Whether you need a fuel sender reed switch, universal fuel sender, diesel fuel sending unit, and more, PartsVu has what you need to get the job done. 

Need help servicing your boat and outboard engine? PartsVu regularly publishes helpful how-to guides and other valuable maintenance information to help boaters service their outboard engines, boats, trailers, and more. Browse the PartsVu Xchange, our outboard maintenance blog, for a wide range of relevant topics and review the FAQ section below, covering everything you need to know about maintaining your boat in confidence.

Fuel Senders FAQ

Why are fuel senders important in boats and outboard engines?

Fuel senders are an important component of boats and outboard engines, as they provide critical information about the fuel level and help ensure the safe and efficient operation of the vessel.

• Safety: It is important to know how much fuel is available to avoid running out of fuel while operating the boat or outboard engine. Running out of fuel can be dangerous, as it can lead to loss of power and potentially cause the boat to drift or become stranded.
• Efficiency: Knowing the fuel level can help the operator plan and optimize the use of fuel, which can improve the efficiency and performance of the boat or outboard engine.
• Maintenance: Monitoring the fuel level can help the operator keep track of fuel consumption and identify any potential issues with fuel usage or fuel system performance.

What is a fuel sending unit?

Fuel senders typically consist of a float that is attached to a variable resistor or another type of sensor. As the fuel level in the tank changes, the float moves up or down, changing the resistance of the sensor. This change in resistance is then translated into a fuel level reading by a gauge or other type of display. 

Also known as a “fuel level sender unit”, “gas sender”, or “fuel gauge sender unit”,  fuel sending units come in a variety of styles, such as a boat gas tank cap with gauge, or may also have additional features like low fuel warning alarms or fuel level alarms to alert the operator when the fuel level reaches a certain threshold.

What is the fuel sending unit connected to in boats?

In a boat, the fuel sending unit is typically connected to the fuel tank. The fuel sending unit is a device that measures the amount of fuel in the tank and sends this information to the fuel gauge on the dashboard. It consists of a float that moves up and down along a rod as the fuel level in the tank changes. The movement of the float is translated into an electrical signal that is sent to the fuel gauge, which displays the fuel level to the operator.

The fuel sending unit is typically located inside the fuel tank, and is connected to the fuel gauge through a wire. The fuel sending unit is an important component of a boat's fuel system, as it allows the operator to monitor the fuel level and ensure that the boat has enough fuel to run. It's important to maintain the fuel sending unit and keep it in good working condition, as a faulty unit can result in incorrect readings on the fuel gauge, which can lead to fuel shortages or other problems.

Should I use a universal fuel sending unit in my boat?

Using a universal fuel sending unit in your boat is generally not recommended. A universal fuel sending unit is a type of fuel level sender that is designed to be used in a wide range of vehicles, including boats, jetskis, and other watercraft. While these types of fuel senders may seem like a convenient and cost-effective option, they are often not a good choice for use in boats.

One of the main reasons to avoid using a universal fuel sending unit in a boat is that they are not always compatible with the fuel gauge. This can result in incorrect readings on the fuel gauge, which can lead to fuel shortages or other problems.

How do I service my 4-stroke outboard fuel system? 

Use a filter wrench to loosen the existing filter element and use caution when removing it as it will be filled with gasoline. A clear plastic or glass container is helpful to dump the filter and examine the contents. A small amount of debris is common, as is a small amount of water after the fuel has had a moment to settle. More significant amounts of water would warrant further investigation.

If your filter’s mounting location allows it, pre-fill the replacement filter with some gasoline to make re-priming the fuel system easier. It is also advisable to use a small amount of grease or engine oil to lubricate the o-ring before installation. Spin on and hand tighten only about a half turn to snug.

Move back to the engine and locate the filter element(s) on the engine. The scope of this service will only include the low-pressure fuel filter and fuel water separator if applicable by model. Mercury recommends that owners do not service their high-pressure fuel filters. Depending on your engine model, the water separator filter (or castle filter) may be removed by using a wrench, standard tools, and a little caution. Unplug the water-in-fuel sensor if applicable and spin the cap off of the housing. Replace the filter element with a fresh one, lube the o-ring with grease or oil, and carefully reinstall the cap.

For most other models, the low-pressure fuel filter is inline where the fuel supply line passes down the side of the cowling. On applicable models, locate the Schrader valve on the fuel system. Cover the valve with a shop rag or towel and depress the valve stem to vent the pressure from the system before service. With the pressure vented, remove the inline filter and replace it with a new one paying particular attention to locate the clamps or zip ties securing the hoses to the filter.

Locate your engine’s primer bulb if applicable and use the primer to pump up the fuel system. You should feel and hear gasoline entering and filling the filter cup. Check for leaks and prime until the bulb becomes firm.

How do I service my 2-stroke outboard fuel system? 

Use a filter wrench to loosen the existing filter element and use caution when removing it as it will be filled with gasoline. A clear plastic or glass container is helpful to dump the filter and examine the contents. A small amount of debris is common, as is a small amount of water after the fuel has had a moment to settle. More significant amounts of water would warrant further investigation.

If your filter’s mounting location allows it, pre-fill the replacement filter with some gasoline to make re-priming the fuel system easier. It is also advisable to use a small amount of grease or engine oil to lubricate the o-ring before installation. Spin on and hand tighten only about a half turn to snug.

Move back to the engine and locate the filter element(s) on the engine. The scope of this service will only include the low-pressure fuel filter and fuel water separator if applicable by model. Mercury recommends that owners do not service their high-pressure fuel filters. Depending on your engine model, the water separator filter (or castle filter) may be removed by using a wrench, standard tools, and a little caution. Unplug the water-in-fuel sensor if applicable and spin the cap off of the housing. Replace the filter element with a fresh one, lube the o-ring with grease or oil, and carefully reinstall the cap.

For most other models, the low-pressure fuel filter is inline where the fuel supply line passes down the side of the cowling. On applicable models, locate the Schrader valve on the fuel system. Cover the valve with a rag or towel and depress the valve stem to vent the pressure from the system before service. With the pressure vented, remove the inline filter and replace it with a new one paying attention to locate the clamps or zip ties securing the hoses to the filter.

Locate your engine’s primer bulb if applicable and use the primer to pump up the fuel system. You should feel and hear gasoline entering and filling the filter cup. Check for leaks and prime until the bulb becomes firm.

How do I choose the right marine fuel for my outboard engine? 

Using the right marine fuel for your boat’s engine is essential for reliable and optimal performance on the water.

Because different makes and models of boat engines require different fuels, using the wrong boat fuel can cause significant damage to internal engine components as well as your boat’s fuel system.

For many boat owners, it’s common to feel a bit unsure as to which type of marine fuel is right for their engine(s). Choosing between different ethanol levels, mixing oil with fuel, and even using diesel can be downright confusing.

Ethanol-free gasoline is produced in a few different octane levels. REC-90 is marketed for boaters and for use in other small engines. It’s an ethanol-free, 90-octane unleaded gasoline blend designed for use in marine and small engines that ethanol found in other gasoline blends can damage.

Ethanol-free gasoline does not come with the corrosive effects of gasoline containing ethanol. You can expect the best performance and lifespan of your boat’s engine from this type of boat gas.

As one of the most widely-available and inexpensive marine fuels, E10 is safe for most boat engines. E10 stands for “10% ethanol content” gasoline. Ethanol was introduced to reduce hydrocarbon emission pollution without substantially affecting performance.

What is the Problem with Ethanol in Marine Fuel?

As a general rule, avoid marine fuel with ethanol or high-ethanol content (anything above 10% ethanol) whenever possible.

Ethanol attracts water and moisture from the air through the fuel tank vent system. This happens due to a process called “phase separation.” When this moisture accumulates at the bottom of the fuel tank or throughout the fuel system, the engine’s performance is dramatically reduced, corrosion forms through oxidizing internal components, and dilutes the gasoline.

To prevent phase separation, boaters have a few methods:

• Install a 10-micron water-separating fuel filter between the fuel tank and the boat engine to keep water and other contaminants out.
• Use a fuel stabilizer in every tank of fuel, either when storing the boat long-term or between fill-ups.

Where can I learn more about fuel senders on my boat and outboard motor?

PartsVu has plenty of resources for everything you need to know about Fuel Senders and related parts for your boat, as well as all models of popular outboard motors. Start with the following guides and be sure to use the search bar to find plenty of other useful guides to maintain your boat in confidence:

• How to Tell if Your Outboard Fuel Pump is Bad - PartsVu
• Be Aware - 5 Common Yamaha F115 4-Stroke Problems
• Most Common Ways Your Yamaha Outboard Engine Will