Mercury Mercruiser Fuel System

Mercury Mercruiser Marine Fuel System Parts - Resources & Information

PartsVu is happy to stock a wide selection of certified Mercury MerCruiser fuel system parts to fit the exact specifications of your engine. Whether you’re looking for Mercury MerCruiser Fuel Pumps, Carburetor Gasket Kits, Carburetor Repair Kits, and other MerCruiser fuel system components, we have what you need to make sure your MerCruiser starts up like new every time.

For more information on Mercury MerCruiser electrical parts and how to perform DIY repairs for your entire engine, check out some of our helpful MerCruiser resources:

• MerCruiser Inboard Maintenance
• MerCruiser Maintenance Parts Library
• Mercury Outboard and Mercruiser Resources Collection

Mercury Mercruiser Fuel System FAQ

What is marine fuel?

Marine gasoline is composed of blends of distillates. Distillates are the evaporated components of crude oil during the distilling process that are condensed from gas state to liquid state. Marine Gas may be compared to diesel, however the main difference is that the density and storage requirements are different.

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.

Boaters can use automobile fuel containing ethanol, however it should be stabilized to prevent internal corrosion due to phase-separation, the process of gas disintegrating into a moisture-heavy mixture. If there’s significant moisture in the gasoline, the fuel’s combustion will be significantly reduced and will eventually become unusable. 

What are common Mercury MerCruiser engine fuel system issues?

One of the most common ways your Mercury MerCruiser motor will break down is a fuel system failure. Whether you’re experiencing an intermittent bog down, substandard performance, or complete engine failure, your fuel system is a common culprit. Let’s look at the most common Mercury MerCruiser fuel system problems:

• Ethanol gasoline: Only use premium low-ethanol gasoline for your Mercury MerCruiser motor. The reason is that ethanol attracts water, causing fuel to dilute through “phase separation.” Additionally, ethanol gasoline can also gunk up fuel lines and fuel system components due to additives used. To help prevent these issues, regularly use a high-quality fuel stabilizer.
• Fuel lines: Check all of your fuel lines. If you discover any breaks or leaks, you should stop using the engine and make any necessary replacements. Also, take a look at any fuel hoses with an interior liner, where the interior liner can break down and clog further upstream.
• Fuel injectors: If your Mercury outboard or Mercury inboard motor is equipped with fuel injectors, you may experience reduced engine performance when debris from within the fuel lines begins to accumulate in and around the nozzles. In this case, you can either manually clean each fuel injector to remove debris accumulation or use E-GO! Blast Fuel Injector Cleaner in your fuel system as a solution.
• Fuel filters: Mercury MerCruiser fuel filters are designed to catch any debris and contaminants that have entered your fuel system. Regularly replace your inline fuel filters according to your Mercury fuel system 100-hour service to keep fuel running freely. While you may be tempted to wash out the fuel filter and reuse it, it’s better to replace it with a new part.
• Fuel pump: A malfunctioning Mercury MerCruiser fuel pump can significantly reduce engine performance and, over time, severely damage other components. If your fuel pump is not working correctly, replace it and any hoses that may have been affected.

How do I perform maintenance on my Mercury MerCruiser fuel system? 

Mercury MerCruiser fuel system maintenance is a critical aspect of 100-hour service. Depending on your application and style of boat, you likely have a fuel-water separating filter aboard your vessel. If you have not seen one, simply follow the routing of your fuel hose from the engine rigging tube backward through the boat. These vary in shape and manufacturer, so be sure to order the identical replacement filter. 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 into and to 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. Larger 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 later. It is also advisable to use a small amount of grease to lubricate the o-ring prior to installation. Spin on and hand tighten only about a half turn to snug.

Continue your Mercury fuel system maintenance by moving back to the engine and locate the filter element in the clear plastic bowl on the front of your block. Depending on your engine model, this filter cup may be removed by using a special cup wrench – or standard tools and a little caution. If applicable, unplug the water-in-fuel sensor and spin the cup off the housing. Again, drain into your clear container and examine the fuel. If your main water separator was free from water, this filter should be as well. Inspect the o-ring on the top of the filter cup and lightly grease for ease of installation or replace if needed. Replace the filter element with a fresh one and reinstall the cup. Use the cup wrench to tighten. Locate your engine’s primer bulb and use the primer to pump up the fuel system. You should observe gasoline entering and filling the filter cup. Check for leaks and prime until the bulb becomes firm. As a tip, primer bulbs work best when the arrow points up, so use any extra hose in the line to help you tilt the bulb vertical.

What are the symptoms of a bad fuel pump on my Mercury MerCruiser motor?

When you try to start your engine, you should be able to hear the sound of the Mercury MerCruiser fuel pump engaging. 

If that familiar sound of the fuel pump engages can’t be heard, there’s a chance it could be due to issues with the battery. Check the battery first, and depending on other symptoms you may be experiencing, it could be a good idea to troubleshoot other systems with one of our Mercury repair guides. Still, if you’re missing that motorized sound, that’s a strong sign that the fuel pump may be having issues.

Another common symptom of a bad fuel pump is sputtering or misfiring. If you’re experiencing a bumpy ride (or possibly losing speed altogether), it could also be a sign of a clogged fuel filter that won’t allow a consistent flow. You’ll want to check the entire Mercury MerCruiser fuel system to ensure that any clogs and blockages in the system are addressed. We outline what parts of the fuel system you need to check in our Mercury MerCruiser and Mercury troubleshooting guides

How do you prevent Mercury MerCruiser motor fuel pump problems?

First and foremost, be sure that you’re performing the required engine maintenance at the recommended intervals. Our guides to engine maintenance for Mercury MerCruisers provide a basic checklist for this process, including all the parts that each manufacturer recommends you check for cracks, leaks, or other signs of damage and wear. 

Generally, fuel pumps themselves should be replaced as needed, but Mercury MerCruiser specifically recommends that outboard fuel pumps should be replaced every 3 years. 

With regular maintenance, the proper Mercury MerCruiser service kit and the right set of tools, most outboard issues are fully preventable. Still, there are a few specific ways to keep your outboard motor’s fuel system in top shape.

Why should I use Mercury fuel stabilizer?

Mercury Quikstor treats and stabilizes fuel at every fill-up which is necessary because just about all gasoline today contains up to 10% ethanol. Left untreated, ethanol-blended fuel can break down, leading to gum and varnish build-up. This buildup then leads to blocked fuel flow and internal engine corrosion due to the moisture content of the water. 

As a preventive measure, fuel stabilizers keep fuel fresh between fill-ups for up to three months. This is also why boaters should use Mercury Quikstor if their boat is stored during winterization or is used infrequently, which can lead to issues with your engine running. Before storage, simply add a bottle of Quickstor to your fuel tank, then run the engine so that the treated fuel circulates throughout the engine and fuel lines. This extended fuel stabilizer prevents gum and varnish from forming in the engine, fuel lines, and tank and stabilizes fuel for up to one year, thereby successfully averting any fuel-related problems. One ounce of Quickstor treats five gallons of fuel, so a 12-ounce bottle treats 60 gallons.