Keeping Your Outboard in Top Condition

MMX CW Service 5.13-12

Keeping a modern outboard running efficiently and reliably is not very difficult if you are diligent with a few preventive maintenance procedures. Learn how you can keep your outboard engine(s) running at their optimum.

Oil and Lubrication

The life blood of any internal combustion engine is the lubricating oil. Two-stroke motors require a mix of oil and fuel. With small outboards the oil is mixed in the portable tank, check the manual for proper mix, typically 50-parts fuel to 1-part 2-stroke engine oil. Larger 2-stroke outboards have in-line mixing where the 2-stroke oil is in a separate tank and mixed with the fuel automatically. Be sure to use premium brand 2-stroke engine oil.

4-stroke motors are similar to automobile engines with oil that cycles through the engine. You should check the engine oil level often. If the oil is low, add oil as needed to the recommended level as indicated on the dipstick. Always use the proper viscosity oil that the manufacturer recommends and use premium brand 4-stroke engine oil, this is not something you want to save a few dollars on.

4-Stroke Oil Change

Change the engine oil as the owner’s manual suggests, typically once a year. Experts recommend that you change the oil with the motor at operating temperature to remove the most oil possible. With the engine not running and the cowling off, open the oil drain port and collect the oil in a drain pan. This can be messy. However, if you use an extraction tube attached to the oil drain port or use an oil extraction vacuum pump with the extraction tube down the dip stick tube.

Let the engine drain completely. Remove the oil filter with an oil filter wrench. Some manufacturers, like some Mercury Marine models, will provide an oil collection container under the oil filter to keep the excess oil in the filter from dripping into the engine shroud. Otherwise a rag placed around the filter is the best way to keep the oil from getting all over. Use the type oil and filters that the owner’s manual recommends. Always use the best quality filters and oil, this is not something you want to skimp on. Put a nice coat of oil on the new filter gasket and screw the new filter into place, hand tight. Emphasis on tight. Close the drain port and add the oil through the oil fill. Tilt the motor up and then down to get the proper engine oil level on the dipstick.

Lower Unit Oil Change

Lower units should have the lubrication oil change annually. It is fairly simple process. You will need a drain pan, a flat head screwdriver, the proper lower unit oil as recommended by the outboard manufacturer, an oil pump with the proper fixture for your outboard model and some rags for cleanup. You can purchase what you don’t have a most marine stores. Place a container under the lower unit to catch the old oil. Remove the lower drain screw plug first. The oil will flow slowly until the upper vent screw plug is removed. Then the oil will flow freely.

Inspect both the oil for emulsification and the magnet at the end of the drain screw plug for metal filings. Emulsification occurs when water gets into the lower unit. The oil will look milky. A small amount emulsification is o.k. However, if it is pervasive or if there are large pieces of metal on the drain screw plug seek out a MarineMax Certified Mechanic about repairing or replacing the lower unit.

To replace the oil use put the proper fixture on the hose end of the pump. Screw fixture into the lower drain plug opening. Put the pump into the oil container by placing the intake into the container and screwing the pump onto the container cap threads. Pump the oil into the lower unit until it come out of the upper vent opening. Replace the upper vent screw plug and snug it tight. Remove the hose and fixture from the lower drain and quickly replace the lower drain screw plug. Wipe all the excess oil from the lower unit with a rag. To protect our oceans, rivers and lakes, put the used lower unit oil in a container and take it to a recycle center or hazardous waste facility.

Flush After Every Trip

Whether you boat in saltwater or freshwater, flushing out the engine after every use is crucial for the life of your engine. Most 2-stroke outboards require flushing devices that fit over the water intakes of the outboard. These are often referred to as “ear muffs” or “rabbit ears.” Simply attach a freshwater hose to the flushing device, slip it over the intakes, make sure the water is on fully and start the engine. Run the motor of 3 to 5-minutes making sure the exiting water stream is strong. Carefully test the temperature of the water coming out, it should be warm not scalding. If the temperature is overly hot, you may need a new water pump. Contact your local MarineMax Service Center for a proper evaluation.

On small outboards with portable tanks it is also recommended that you disconnect the fuel while the engine is running until it stalls. This assures that all the fuel in the carburetor is removed.

For most 4-stroke outboards and many modern larger 2-stroke outboards there is a back-flush port that allows the engine to be thoroughly flushed without running the motor. It has the added benefit of forcing sand or debris that may have been sucked through the intake out of the engine. Before connecting the freshwater hose, run the water for a bit to make sure there is nothing that has gotten into the hose such as bugs, lizards or debris. These are not good things to put through your outboard.


Even though it may be more than a dollar more per gallon at the fuel dock, use marine grade fuel without ethanol. This is an expense you really don’t want to get cheap with. Ethanol absorbs moisture and separates over time with the water settling on the bottom of the tank where the fuel pickup resides.


Check under the cowling and around the engine shroud for fuel or water leaks.

Clean and lubricate all moving parts by spraying anti-corrosive lubricants as the manual recommends.

Check fuel lines, primer bulb, fittings and clamps for damage, wear or corrosion.

Check the fuel tank and fuel tank vent for damage, corrosion or blockage.

All of the maintenance procedures described are critical to the life of your outboard. Especially the 4-stroke and the lower unit oil changes. The results, if oil changes are not done properly, could be severe. If you are not mechanically inclined or are unsure of how to proceed, your local MarineMax Service Center has factory certified mechanics that can provide excellent service at reasonable prices.

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