Mercury Outboard Cylinder Heads & Blocks

Mercury Marine Engine Cylinder Heads and Blocks Resources and Information

A cylinder block is the part of an engine containing the cylinders. The cylinder block acts as the central frame of the engine, and all the other engine components are attached to it. Maintaining your Mercury outboard cylinder heads and blocks is essential for prolonging your marine engine life. Take a look at this helpful guide over on our blog to learn how to protect your Mercury outboard motor. 

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

• Mercury Outboard Engine Schematics
• Mercury Outboard Service Schedule
• Mercury Outboard Specs & Capacities Chart

Mercury Outboard Cylinder Heads and Blocks FAQs

What is an outboard cylinder head?

An essential part of the Mercury outboard powerhead, the cylinder head sits above the cylinders and houses camshafts, sparkplugs, cams, and shafts. 

What is an outboard block?

The outboard engine block contains all the moving components of your Mercury outboard engine. The crucial components housed within the outboard engine block include piston rods, pistons, the crankshaft, and the cylinders.

How do I select the right parts for my Mercury outboard motor?

PartsVu’s Mercury Outboard Maintenance Parts Library is the perfect reference when you need to replace common parts. That’s because these parts charts make it simple to find the right parts for your particular engine to perform regularly-scheduled maintenance. 

For Mercury outboard motors, perform maintenance after 100 hours of service or one year of operation (whichever comes first). More extensive service is recommended after 300 hours of service or three years.

After this period, maintenance is often more regular as the engine ages and parts wear out. For example, 1,000 hours generally requires an in-depth assessment by a qualified mechanic. Also, if you’re usually running your Mercury outboard in a more demanding manner, the manufacturer recommends more frequent servicing.

When selecting the correct Mercury Outboard Parts, there are some essential things every boater must keep in mind before purchasing and installing parts:

• Choosing Mercury OEM parts (original equipment manufacturer) over after-market parts often yields better long-term results for your engine as these components and products are specifically designed to meet the precise tolerances of Mercury engines.

• Check (and recheck) to ensure that you have the exact part number that matches your Mercury outboard engine. It’s important to do this because Mercury has many engine models that look very similar but contain slight differences in performance. Therefore, unmatched parts may not fit uniformly, leading to malfunctions, underperformance, and severe engine damage.

• Proper maintenance is essential when it comes to extending the life of your Mercury outboard motor and should always be mandatory to retain the value of your outboard motor. While Mercury outboards are built to last, hazards like salt water, humidity, excessive heat, electrolysis, and demanding usage eventually take their toll on your motor.

• Proper storage for your Mercury outboard is required to preserve your motor for the long term. Failure to properly winterize your Mercury outboard can cause components to degrade while the engine sits and is exposed to the elements. Therefore, properly store your outboard when it is not in use.

PartsVu offers more than 54,000 genuine Mercury OEM parts and products and other boating essentials at affordable prices. With same business day shipping on in-stock items, PartsVu is always by your side to find the right parts every time. Enjoy optimal performance and lifespan from your Mercury outboard motor today!

Will doing maintenance void my Mercury outboard engine warranty?

Any warranty work done on your engine needs to be done by an authorized Mercury dealer. Your dealer will perform the work on your engine and file the claim with Mercury for you.

Your Mecury’s warranty does not apply to damage or failures caused by use of an accessory or part not manufactured or sold by Mercury. See the appropriate Mercury or MerCruiser warranty policy for your product or in your Operation, Maintenance & Warranty manual. In other words, if you modify your engine with non-Mercury parts and those parts cause damage, you will likely have a problem.

Fuels containing up to 10 percent ethanol are considered acceptable for use in Mercury engines. Fuels containing higher levels of ethanol are not considered acceptable for use, and can void the warranty.

Using the serial number of your engine, your local authorized Mercury dealer can quickly check your warranty coverage. They can verify that your engine is registered with Mercury, whether it is covered by Mercury’s standard factory warranty, if there is any additional promotional coverage, or if it is covered by a Mercury Product Protection plan.

How do I troubleshoot my Mercury outboard engine?

If your Mercury outboard cranks, but won’t start, there may be an issue that needs correcting. 

Most likely, the cause is a low and dying battery. Remove the battery from its housing by first disconnecting the black (negative) cable, and then the red (positive). You can then check the voltage using a voltmeter– it should be at about 12.6 volts. Inspect the battery for damage and clean off any corrosion or other buildup with a wire bristle brush. 

Some types of residue can be removed with a mixture of water and baking soda at a ratio of 1 cup:1 tablespoon, respectively. Apply and scrub the mixture over the affected parts. If you choose to do this, be sure to very thoroughly dry the battery before reattaching the cables. Finally, if the voltmeter resulted in a low reading, charge the battery. 

In cases where your battery won’t hold a charge, it will of course need to be replaced. In the meantime, you may be able to start the engine manually.

How often should I grease my Mercury outboard grease points?

You must grease all points at regular service intervals—minimally, annually. Saltwater boaters need to lubricate much more frequently as saltwater breaks down grease, and saltwater on non lubricated surfaces causes a great deal of damage.

Refer to your owner’s manual to locate all the grease fittings on your specific engine. Most will be easy to find, but a couple are likely tucked away and are not quite as visible. While you must familiarize yourself with the grease fittings on your specific engine, common grease fitting points include:

• Steering friction adjustment shaft (tiller handle models) 
• Swivel bracket
• Tilt tube
• Steering cable grease fitting

To add grease, first wipe off the grease fitting before attaching the grease gun nozzle to avoid pumping dirt and debris into the grease point. Also, you may have to remove rust and other debris clogging/blocking grease fittings. 

Pump grease into the fitting until grease begins oozing out of the exit points of the area being greased. The old grease will be pushed out as it is being dislocated by the new grease. Wipe off the old grease with your rag.

When a given grease point is full, leave a bit of grease on top of the grease fitting to keep rust and other debris from accumulating. Wipe off any excess grease with your rag, then move to the next grease fitting.

While not needed for all scenarios, it is worth noting that Mercury’s High Performance Extreme Grease is formulated for high temperature and high load applications and 100% compatible with lithium-based greases.

How do I protect my Mercury outboard motor?

Cover it with Corrosion Guard. This rust inhibitor forms a water-resistant barrier on both painted and unpainted surfaces. We recommend using it at every service interval with a liberal application to all metal engine surfaces. You can also use it on outdrives, lower units, and power trim motors.

The marine environment is one of the harshest on the planet. This is why protecting your boat from corrosion is extremely important. For premium defense against rust, we highly recommend this product.

In order to maximize your engine’s performance, use this complete fuel treatment at every fill-up with any grade of gasoline. Quickare is an excellent defense against the problems associated with ethanol-blended fuels, including its corrosive effects on metals as well as the gum and varnish that result from fuel oxidation. See PartsVu’s Knowledge Center for our article on the problems of ethanol gasoline.

This product can also be used to clean up existing deposits in untreated fuel lines, tanks, carburetors, injectors, intake valves, and spark plugs. It will keep your fuel fresh for up to three months and can be used in all 2 and 4 cycle carbureted and fuel-injected gasoline engines. Use one ounce to treat every 10 gallons of fuel.

What tools do I need for a Mercury outboard cylinder block cover removal?

To remove the cylinder block cover on a Mercury outboard, you will need the following tools:

1. Socket set: A set of sockets in various sizes will be necessary to loosen and remove the bolts securing the cylinder block cover.
2. Wrenches: A set of wrenches, including both open-end and adjustable wrenches, will be useful for certain bolts or fasteners that are not easily accessible with a socket set.
3. Screwdrivers: Both flathead and Phillips screwdrivers may be required to remove any screws or fasteners holding the cylinder block cover in place.
4. Torque wrench: Once you have completed the repairs or maintenance and are ready to reinstall the cylinder block cover, a torque wrench will ensure that the bolts are tightened to the specified torque value.
5. Gasket scraper: Depending on the condition of the old gasket, a gasket scraper can be helpful in removing any remnants of the previous gasket from the cylinder block and cover surfaces.
6. Shop towels or rags: Having some shop towels or rags on hand will be useful for wiping away any oil or debris that may be present during the removal process.

It's important to consult your engine's specific service manual for the recommended procedures and torque specifications for removing and reinstalling the cylinder block cover. Following the manufacturer's guidelines will help ensure a successful and safe removal process.

Do Mercury 3.0 liter outboards crack cylinder heads?

Cracking of cylinder heads can occur in any engine, including Mercury 3.0 liter outboard engines. However, it is not a common or widespread issue specific to Mercury 3.0 liter outboards. The likelihood of cylinder head cracking depends on various factors, such as engine maintenance, operating conditions, and usage.

Cylinder head cracking can be caused by several reasons, including overheating, improper engine cooling, poor maintenance, or manufacturing defects. To minimize the risk of cylinder head cracking, it is important to properly maintain and monitor your Mercury 3.0 liter outboard engine.

Ensure that the engine is adequately cooled by regularly inspecting and maintaining the cooling system, including the water pump, thermostat, and hoses. Maintain proper engine temperature by monitoring the cooling system during operation and avoiding prolonged operation at high RPMs without adequate water flow.

Additionally, following the manufacturer's recommended maintenance schedule, including regular inspection of the engine components and addressing any issues promptly, can help prevent potential problems and extend the life of your engine.

If you suspect or observe any signs of cylinder head issues, such as coolant leaks, loss of compression, or engine overheating, it is recommended to have the engine inspected by a qualified marine technician who can diagnose the problem and recommend appropriate repairs.

It is important to note that cylinder head cracking is not a widespread or common issue with properly maintained Mercury 3.0 liter outboard engines, but regular maintenance and prompt attention to any issues can help minimize the risk of such problems.

Where can I learn more about Mercury outboard parts and maintenance?

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 engine maintenance.

To get you off to a good start, these are some of the most important articles on Mercury Cylinder Heads & Blocks, best practices for Mercury outboard cylinder block gasket replacement, and more:

• Marine Corrosion - Corrosion Types and What to Do About ...
• Does Your Yamaha Outboard Head Gasket Need to be ...
• How to Start a Mercury Outboard Motor
• Mercury Fuel Additives for Performance and Engine Life

What are cylinder heads and blocks on a Mercury outboard engine?

Cylinder heads and blocks are two essential components of a Mercury outboard engine's combustion chamber. The cylinder head sits on top of the engine block and seals the cylinders, allowing the combustion process to occur.

How do I know if the cylinder head or block on my Mercury outboard engine is damaged?

Signs of a damaged cylinder head or block include engine misfires, loss of power, decreased fuel efficiency, and coolant leaks. If you notice any of these signs, it is recommended to have your engine inspected by a qualified technician.

Can I replace the cylinder head or block on my Mercury outboard engine myself?

Replacing the cylinder head or block on a Mercury outboard engine is a complex task that requires specialized knowledge and tools. It is recommended to have a qualified technician perform the replacement to ensure that it is done correctly and safely.

How often should I have the cylinder head and block inspected on my Mercury outboard engine?

It is recommended to have the cylinder head and block inspected at least once a year or every 100 hours of operation to ensure that they are functioning correctly and are not showing signs of damage or wear.

What materials are used in Mercury outboard cylinder heads and blocks for durability and longevity?

Mercury outboard cylinder heads and blocks are typically made of high-quality materials such as aluminum or cast iron. These materials are chosen for their durability, resistance to wear and corrosion, and ability to withstand the harsh marine environment.

What are cylinder heads and blocks in a Mercury outboard engine?

The cylinder head and block are essential components of the engine's combustion chamber. The cylinder block houses the cylinders, while the cylinder head sits on top of the block and seals the combustion chamber.

What is the function of a cylinder head in a Mercury outboard engine?

The cylinder head has several functions in a Mercury outboard engine, including sealing the combustion chamber, housing the valves and valve springs, and providing a mounting surface for the engine's accessories.

What is a reed block in a Mercury outboard engine?

A reed block is a component in a Mercury outboard engine's intake system that controls the flow of air and fuel into the combustion chamber. It contains thin metal reeds that open and close as the engine runs, allowing air and fuel to enter the engine.

How often should I check the cylinder heads and blocks on my Mercury outboard engine?

It is recommended to have the cylinder heads and blocks inspected by a qualified technician at least once a year or every 100 hours of use. This inspection will ensure that the components are in good working condition and identify any potential issues that may require repair or replacement.

Can I replace the cylinder heads or blocks on my Mercury outboard engine myself?

Replacing the cylinder heads or blocks on a Mercury outboard engine is a complex and technical process that requires specialized knowledge and tools. It is recommended to have a qualified technician perform this type of repair to ensure that it is done correctly and safely.

What is the optimal Mercury outboard cylinder head operating temperature?

The optimal operating temperature for Mercury outboard cylinder heads typically falls within a range of 160 to 200 degrees Fahrenheit (71 to 93 degrees Celsius). This temperature range allows the engine to operate efficiently and ensures proper combustion within the cylinders.

It's important to note that the exact operating temperature may vary depending on factors such as the specific model of the outboard engine, ambient temperature, load conditions, and running speed. Mercury outboard engines are designed to operate within a specified temperature range to promote optimal performance and longevity.

To monitor the cylinder head temperature, most Mercury outboard engines are equipped with temperature sensors or gauges that provide real-time temperature readings. If you notice that the temperature consistently exceeds the recommended range or shows signs of overheating, it is crucial to address the issue promptly. Overheating can lead to engine damage and performance issues, so it's advisable to consult a professional technician or refer to the engine's service manual for troubleshooting and repairs.

Is the Mercury outboard cylinder head cover gasket covered by a warranty?

The warranty coverage for the Mercury outboard cylinder head cover gasket may vary depending on several factors such as the specific engine model, warranty terms and conditions, and the reason for the gasket failure. Typically, gaskets are considered wear and tear items and may not be covered under the standard warranty.

To determine the warranty coverage for the cylinder head cover gasket, it is recommended to consult the official warranty documentation provided by Mercury or reach out to an authorized Mercury dealer or service center. They will have the most accurate information regarding warranty coverage and can guide you through the process of filing a warranty claim if applicable.

Keep in mind that warranties often have specific requirements and limitations, such as the engine being properly maintained and serviced according to the manufacturer's guidelines. It's essential to review the warranty terms and conditions to understand the extent of coverage for gaskets or any other components.

Is there a tool to test a faulty Mercury outboard cylinder head temp sensor?

Yes, there are tools available to test a faulty Mercury outboard cylinder head temperature sensor. One commonly used tool is a multimeter, which is a versatile electronic testing device. Here's a general procedure to test the cylinder head temperature sensor using a multimeter:

1. Ensure the engine is turned off and the ignition is off.
2. Locate the cylinder head temperature sensor on the engine. It is usually positioned near the cylinder head or attached to the cooling system.
3. Disconnect the electrical connector from the sensor.
4. Set the multimeter to the resistance (ohms) mode.
5. Touch the multimeter leads to the terminals of the temperature sensor. The specific terminals will depend on the sensor design.
6. Observe the multimeter reading. Compare it to the specifications provided in the Mercury outboard service manual or technical documentation.
7. If the resistance reading falls within the acceptable range, the sensor is likely functioning correctly. If the reading is outside the specified range, the sensor may be faulty and require replacement.

It's important to note that the exact testing procedure and acceptable resistance values can vary depending on the specific model and year of your Mercury outboard. It's always recommended to refer to the official service manual or consult a qualified technician for accurate testing instructions for your particular engine.

How long does it take for a new cylinder head to break in?

The break-in period for a new cylinder head in a Mercury outboard engine typically depends on various factors, including the engine model, its specifications, and the manufacturer's recommendations. It's important to follow the specific guidelines outlined in the engine's owner's manual or the manufacturer's documentation for the most accurate information. However, as a general guideline, the break-in period for a new cylinder head is often considered to be around 10 to 20 hours of operation.

How is a 3.0 MerCruiser cylinder head different than a Mercury outboard cylinder head?

The main difference between a 3.0 MerCruiser cylinder head and a Mercury outboard cylinder head lies in their design and intended use. While both are manufactured by Mercury Marine, they are specifically designed for different applications.

A 3.0 MerCruiser cylinder head is designed for use in MerCruiser stern-drive engines, which are typically used in boats for propulsion. These engines are often used in larger vessels and require specific components to handle the higher loads and demands of marine propulsion. The 3.0 MerCruiser cylinder head is designed to work in conjunction with the rest of the MerCruiser engine system, including the exhaust system, cooling system, and other components specific to stern-drive applications.

On the other hand, a Mercury outboard cylinder head is designed for use in outboard engines, which are typically mounted on the transom of smaller boats. Outboard engines provide propulsion and steering control, and they are designed to be lightweight, compact, and easily maneuverable. The cylinder head in a Mercury outboard engine is designed to meet the specific requirements of these engines, including efficient cooling, power delivery, and integration with the outboard's overall design.

While there may be some similarities in terms of materials and manufacturing techniques between the two cylinder heads, they are engineered differently to cater to the specific needs and operating conditions of their respective engine types. It's important to use the correct cylinder head designed for your specific engine type to ensure optimal performance and compatibility.