Mercury Outboard Anodes & Anode Kits

Mercury Marine Engine Anodes Resources and Information

PartsVu is happy to offer a complete selection of Mercury Outboard Anodes to protect the vital components of your Mercury outboard engine. Shop our collection of zinc anodes, aluminum anodes, and magnesium anodes. If you need help installing an anode on your outboard, check out this helpful guide on our official blog. We also stock Mercury Anode Kits to make your outboard anode installation a snap.

We also offer helpful resources to help you maintain your Mercury outboard motor, such as:

• Mercury Outboard Service Schedule
• Mercury Outboard Specs & Capacities Chart
• Mercury Outboard 100-hour Service Guides

Mercury Outboard Anodes FAQs

What does a trim tab anode do on an outboard motor?

Trim tabs are essential for steering your boat safely and accurately. When properly aligned, trim tab anodes counteract torque pressure generated by the propeller for steering and helps even out “prop-walk,” a propeller’s tendency to rotate about a vertical axis. That’s why it’s called a “trim” tab, enabling a more stable ride that offsets unwanted torque. Trim tabs are often set at an offset angle for this purpose – aligned right for right-turning outboard motors and left for left-turning outboard engines. Most Mercury outboards have a series of hash marks by the trim tab that indicate the offset needed for accurate steering.

There are three types of corrosion boaters typically experience:

• Simple electrochemical corrosion
• Galvanic corrosion
• Electrolytic/stray current corrosion

Trim tab anodes absorb these types of corrosion more readily than other engine components, so they serve as a protective barrier to save more expensive and harder-to-repair parts. 

Over time, these anodes—typically made of cheap zinc materials—will degrade and need to be replaced. As the material degrades, it begins to lose some of its steering abilities and its ability to attract corrosion. While simply cleaning it with a wire brush will restore it for minor damage, replacement is necessary when corroded to approximately half of its original size. This is why they are referred to as sacrificial anodes—the anode sacrifices itself to protect your engine and its components. 

Checking your trim tab anode(s) (and other anodes, for that matter) should be done minimally as part of your annual or 100-hour service.

How do I install a trim tab anode?

Now that you understand why trim tab anodes are important for your boat and outboard motor, let’s learn how to install trim tab anode on Mercury outboards:

• First, identify where the trim tab anode on your Mercury outboard is. It is typically located above the propeller on the anti-cavitation plate.
• Next, locate and remove the trim tab plug located directly above the trim tab. 
• In the cavity, you will insert a socket wrench with an extension to access the bolt securing the trim tab. Most Mercury trim tabs use a ½” socket wrench.
• Make a note of the hash marks by the trim tab, which indicates how many degrees they will be offset. Use a piece of masking tape if you have to remember the location so you won’t have to adjust it after installation.
• Slowly turn the bolt counterclockwise to loosen the trim tab until it loosens.
• Insert the new trim tab anode. Replacement is the opposite of installation.

That’s the entire process for replacing a trim tab on a Mercury outboard motor. Simple!

What is the best anode for freshwater?

The best anode for freshwater is made from magnesium. While aluminum and zinc are cheaper alternatives, serving as “catch-all” materials, magnesium helps prevent “potential reversal” at elevated temperatures commonly found in freshwaters. This means that materials besides magnesium may actually draw in unwanted corrosion and electrolysis, especially in marinas where boaters use land power.

Therefore, if you are looking to take your boat out from saltwater to freshwater, it may be wise to perform a Mercury outboard anode replacement with magnesium anodes.

What kinds of corrosion affects outboard anodes? 

Direct current (DC) stray current corrosion is the corrosion that occurs when current flows through metal and water as it seeks a path back to battery ground. The corrosion rate caused by stray DC current can be 100 times the rate of galvanic corrosion, and it can cause significant damage in day, or even hours. In extreme cases of stray current corrosion a lower unit and outdrive housing can be eaten almost completely away, exposing the shafts and gears. While this certainly does happen, there are other more common cases of stray current corrosion that occur, some that are easily – but mistakenly – attributed to galvanic corrosion. There is a fairly common stray current situation which occurs on multi-engine boats. Often, the stainless-steel propeller on one motor has a dull surface and the other is still shiny and clean.

Electrochemical corrosion, also referred to as self-corrosion, only requires a piece of metal to be in contact with an electrolyte. In this case, the metal is both the anode and the cathode, as well as the conductive path. How can a single piece of metal be both an anode and cathode? Most metals are actually alloys, meaning they contain multiple base metals and impurities. In an alloy, one base metal functions as the anode, while another base metal functions as the cathode. The electrolyte can be plain old air, a liquid, or a combination of both. Examples we commonly see would be the formation of rust on steel or a layer of oxide on bare aluminum. This process, although extremely slow, begins as soon as most metals are manufactured and may be the easiest form of corrosion to slow down. A protective coating, such as the correct kind of paint, can slow the process way down.

Galvanic corrosion typically involves two dissimilar metals, aluminum and stainless steel. These metals are bonded together either by direct contact or by the electrical system and are submerged in an electrolyte – the water the boat is in. The assortment of these elements essentially becomes a big wet cell battery.

What happens in a battery when a connection is made between the positive and negative posts? Electrons flow between the battery’s plates, which are anodes and cathodes. On a boat without any corrosion protection, aluminum, being the most active metal, will become the anode and the stainless steel, a less active metal, will be the cathode. Electrons will flow from the anode to the cathode, resulting in a loss of anode material, visible as corrosion on the aluminum components.

What is a sacrificial anode? 

• The factory-installed anodes must be in the water to provide protection.
• Trim tab anodes may not be in the water when the lower unit is tilted up.
• Transom bracket anodes may not be in the water on motors installed in applications requiring extremely high mounting.
• Additional anodes are required when other metal components are in the system: aluminum hulls, jack plates, trim tabs*, trolling motors, etc. The motor’s anodes not only will be unable to protect the other components, but will also be unable to protect the motor. They will also erode extremely quickly. Additional anodes may be required on a motor when used in applications other than what it was originally designed for. Example: SHO® models, primarily a freshwater bass boat motor, may need more anodes when used in saltwater, brackish water, and even when regularly moored in freshwater. 
• Anodes must be clean and free of paint to work properly.
• Anodes must be electrically conductive and connected to the boat and motor’s grounding system. Conductivity through the anode material and between the anode and the boat’s electrical system deteriorates with time and exposure.
• By design, anodes deteriorate as they provide protection and must be replaced periodically. Replace anodes when they have eroded to 2/3 their original size. Beware, looks can be deceiving. Anodes can lose mass (weight) without visibly looking smaller. Did you ever see one that looked like it was full of worm holes?
• Water flow around a moored boat can disrupt the flow of electrons from the anode to the cathode. If the electrons from the anode do not make it to the cathode, the anode will shed even more electrons at a faster rate in its valiant effort to protect the cathode.
• Boats connected to shore power could be electrically connected to other boats and dock structures through the common grounding wire (green) in the AC power system, forming one huge system. Anodes on one boat will try to protect other boats or submerged dock structures that do not have sufficient anode protection of their own. A galvanic isolator installed near the boat’s shore power receptacle in the AC grounding (green) wire blocks the flow of galvanic current between boats and dock structures connected to a shore power system.

When should I replace my Mercury outboard’s anode?

The anode in your Mercury outboard motor is designed to protect the engine from corrosion by sacrificing itself instead of the metal parts of the engine. Over time, the anode will gradually deteriorate and lose effectiveness, so it's important to replace it when necessary.

The frequency with which you should replace your anode depends on a variety of factors such as the type of water your boat is used in, the frequency of use, and the condition of the anode. However, a good rule of thumb is to check the anode every six months or 100 hours of use, whichever comes first. If the anode is more than 50% depleted, it should be replaced.

It's also a good idea to replace the anode whenever you notice signs of corrosion on your engine or if you experience electrical problems such as electrolysis. Additionally, if you store your boat for an extended period, it's recommended that you replace the anode before putting the boat back in the water.

What metal anode is best?

The best metal anode depends on the specific operating environment of your boat. Different metals are better suited for different types of water, and selecting the right metal anode can help ensure the best possible protection against corrosion.

Zinc anodes are the most commonly used anodes and are ideal for use in saltwater environments. They provide excellent protection against corrosion in highly conductive water, but they tend to corrode faster than other anode materials.

Aluminum anodes are a good choice for both freshwater and saltwater environments. They are less susceptible to galvanic corrosion and tend to last longer than zinc anodes in some saltwater conditions.

Magnesium anodes are the best choice for use in freshwater environments as they offer excellent protection against corrosion in low conductivity water. However, magnesium anodes should not be used in saltwater or brackish water as they corrode too quickly.

In general, it's essential to select an anode that is appropriate for the specific environment in which you will be operating your boat. Consulting with a certified technician or referring to the engine's owner's manual can help you choose the correct type and size of anode for your specific boating environment.

What is the best anode for salt water?

The best type of anode for saltwater boats is typically made of zinc or aluminum. Zinc and aluminum anodes are the most commonly used anodes in saltwater environments because they provide excellent protection against corrosion in highly conductive water.

Zinc anodes are typically more effective than aluminum anodes in saltwater environments, but they also tend to corrode faster. On the other hand, aluminum anodes are less susceptible to galvanic corrosion and tend to last longer in some saltwater conditions, but they may not provide as much protection as zinc anodes.

It's important to note that magnesium anodes are not recommended for use in saltwater environments as they tend to corrode too quickly, which can lead to damage to the boat's metal components.

When selecting an anode for your saltwater boat, it's crucial to refer to the manufacturer's recommendations or consult with a certified technician to ensure that you choose the correct type and size of anode for your specific boating environment. Additionally, it's essential to inspect the anodes regularly and replace them if they show signs of excessive corrosion or wear.

What’s the purpose of anode on outboard engines?

The anode on an outboard engine serves as a sacrificial metal that protects the other metal components of the engine from corrosion. An outboard engine operates in a harsh environment that exposes it to seawater, which is a highly corrosive substance.

The anode is typically made of zinc or aluminum, which are more reactive than the metals in the engine, such as steel or aluminum. As a result, the anode corrodes instead of the engine's metal components, preventing them from deteriorating.

The anode should be inspected and replaced periodically as part of routine maintenance to ensure that it continues to provide adequate protection. If an anode is not replaced when necessary, the engine's metal components could corrode and potentially fail, leading to expensive repairs or replacement.

Can a Mercury outboard anode replacement be performed by most boaters?

Yes, replacing a Mercury outboard anode can be performed by most boaters with basic mechanical skills.

To replace the anode, you will need to locate it on the engine, which is typically located on the lower unit, near the propeller. Then, using a socket wrench or pliers, you can remove the old anode and replace it with a new one.

It is important to refer to the owner's manual or consult with a certified Mercury technician to ensure that you are using the correct type of anode and properly installing it.

Also, it is essential to follow safety precautions such as turning off the engine and disconnecting the battery before starting any maintenance work. If you are unsure about the replacement process, it's best to have a professional perform the maintenance.

What is included in a Mercury outboard zinc anode kit?

A Mercury outboard zinc anode kit typically includes several zinc anodes that are designed to fit specific models and sizes of outboard engines. The kit may also include mounting hardware such as screws, bolts, or nuts to attach the anodes to the engine.

In addition, some kits may also come with a gasket or sealant to ensure a proper seal between the anode and the engine, as well as instructions or guidelines for installing and replacing the anodes.

It's essential to verify that the anode kit you purchase is suitable for your specific engine model and size. The anode's weight, shape, and location on the engine can affect its effectiveness in protecting the engine from corrosion.

What is the best anode for fresh water boats?

The best type of anode for fresh water boats is typically made of magnesium. Magnesium anodes are ideal for use in freshwater environments because they offer excellent protection against corrosion in low conductivity water, such as freshwater.

Magnesium anodes work by corroding instead of the boat's metal components, which helps to prevent damage to the boat's hull, propeller, and other underwater metal parts.

However, it's essential to note that magnesium anodes are not suitable for use in saltwater or brackish water as they corrode too quickly in these environments. For saltwater or brackish water boats, zinc or aluminum anodes are typically the best choice.

How long does a Mercury lower unit anode last?

The lifespan of a Mercury lower unit anode can vary depending on several factors, including the type of anode, the quality of the water in which the boat is operated, and the frequency of use.

In general, zinc anodes typically last longer than aluminum anodes, but they can still corrode relatively quickly in highly conductive water or water with a high salt content.

As a rule of thumb, most manufacturers recommend replacing lower unit anodes once a year or after every 100 hours of use, whichever comes first. However, it's essential to inspect the anode regularly and replace it if it shows signs of excessive corrosion or wear.

It's crucial to replace the anode promptly to ensure that your boat's metal components remain protected from corrosion. If the anode becomes too corroded, it may no longer offer sufficient protection, which could lead to damage or failure of the engine's metal components, resulting in costly repairs or replacement.

Should I replace Mercury outboard aluminum anodes before winterizing?

If your Mercury outboard aluminum anodes are showing signs of wear or have been in use for a while, it's a good idea to replace them before winterizing your boat. This is because the anodes play a crucial role in protecting your boat's metal components from corrosion, and a worn-out anode may no longer be providing adequate protection.

Winterizing your boat involves several steps, including flushing the engine with fresh water, changing the oil, and draining the cooling system. During this process, you may also want to inspect the anodes for signs of wear and replace them if necessary.

It's generally recommended to inspect and replace the anodes at least once a year or after every 100 hours of use, whichever comes first. However, if you operate your boat in harsh or highly conductive water conditions, you may need to replace the anodes more frequently.

Where can I learn more about Mercury outboard parts?

PartsVu understands that boaters want to learn how to perform their own Mercury outboard maintenance. From maintaining your Mercury outboard, Mercury sterndrive, and MerCruiser engines, there’s always something new to learn and save money. That’s why PartsVu offers our comprehensive blog, The PartsVu Xchange. 

Read up on the latest developments in boating, as well as search for everything you need to know about Mercury anode maintenance.

To get you off to a good start, these are some of the most important articles on choosing the right anode kit for Mercury outboard engines, how to replace Mercury 150 four stroke anodes, and more:

• The Mighty Sacrificial Anode — A Small, Inexpensive Part ...
• How To Protect Your Mercury Outboard
• Marine Corrosion - Corrosion Types and What to Do About ...
• Mercury Mercruiser Inboard Maintenance

Do aluminum anodes conduct electricity in a Mercury outboard motor?

Yes, aluminum anodes conduct electricity in a Mercury outboard motor. Anodes are sacrificial metal parts that are installed on the engine to protect it from galvanic corrosion, which occurs when dissimilar metals are in contact with each other in a saltwater environment. When the engine is in the water, the aluminum anodes on the engine's lower unit and other exposed metal parts form an electrical circuit with the surrounding water. This creates a small electric current that causes the anodes to corrode instead of the more critical engine parts. Over time, the anodes wear away and need to be replaced to continue providing adequate corrosion protection.

Besides an anode, outboard motor corrosion is also likely to occur where else?

In addition to anodes, outboard motor corrosion can also occur in several other areas of the engine and boat:

1. Propeller and Lower Unit: The propeller and lower unit are in constant contact with saltwater, which can cause corrosion over time. Regular cleaning and maintenance can help prevent buildup of salt and other corrosive materials.
2. Stainless Steel Components: Stainless steel components such as steering cables, fuel tanks, and brackets can also corrode in saltwater environments. Use of compatible metals, corrosion inhibitors, and regular maintenance can help prevent corrosion.
3. Electrical Connections: Saltwater can corrode electrical connections and cause electrical problems. Use of dielectric grease, protective covers, and regular cleaning and maintenance can help prevent electrical corrosion.
4. Aluminum Components: Aluminum components such as the engine block, powerhead, and exhaust system can also corrode in saltwater environments. Use of compatible anodes, cleaning and maintenance, and protective coatings can help prevent aluminum corrosion.
5. Paint and Coatings: Damaged or worn paint and coatings can expose metal components to saltwater and accelerate corrosion. Regular inspection and maintenance of paint and coatings can help prevent corrosion.
6. Hull and Trailer: Corrosion can also occur on the boat's hull and trailer in saltwater environments. Regular cleaning and maintenance, use of protective coatings and sacrificial anodes, and proper storage can help prevent corrosion.

By being aware of these potential areas of corrosion and taking appropriate preventive measures, you can help extend the life of your outboard motor and ensure optimal performance and safety.

When should I replace a sacrificial anode on my Mercury outboard

Sacrificial anodes are designed to corrode over time to protect other metal components of your Mercury outboard from galvanic corrosion. These anodes should be replaced periodically to ensure they continue to provide proper protection. The frequency of replacement can depend on a variety of factors, such as the water conditions in which your boat is used, the amount of usage, and the type of anode being used.

As a general rule of thumb, it is recommended to inspect the anodes annually and replace them if they are more than 50% corroded. For boats used in saltwater, it may be necessary to inspect and replace the anodes more frequently, as the saltwater can accelerate the corrosion process.

What's the differences between a Mercury Verado anode kit and a Mercury optimax 150 anode kit?

The main differences between a Mercury Verado anode kit and a Mercury Optimax 150 anode kit are the types of anodes included in each kit and the specific components they are designed to protect.

A Mercury Verado anode kit typically includes a variety of anodes, such as trim tab anodes, transom anodes, and engine block anodes, that are specifically designed to protect the various components of Verado outboards from galvanic corrosion. Verado outboards are high-performance four-stroke engines that are generally used in larger boats and may require more comprehensive anode protection.

On the other hand, a Mercury Optimax 150 anode kit typically includes fewer anodes and is designed specifically for the Optimax 150 two-stroke outboard engine. This kit may include anodes for the engine block, trim tab, and/or gearcase, depending on the specific components that require protection.

It's important to use the correct Mercury outboard anode kit for your specific outboard engine to ensure proper protection from galvanic corrosion. Consult your owner's manual or a qualified Mercury dealer or marine technician to determine the appropriate anode kit for your engine.

How do I store Mercury 150 hp anodes?

To store Mercury 150 hp anodes, it is important to keep them in a dry and cool location. Moisture and high temperatures can accelerate the corrosion process, reducing the effectiveness of the anodes. Here are some steps you can follow to properly store your Mercury 150hp anodes:

1. Remove any dirt or debris from the anodes using a soft brush or cloth.
2. Inspect the anodes for signs of excessive corrosion or damage. If any anode appears to be more than 50% corroded, it should be replaced before storage.