Outboard Engine 100-Hour Service Checklist

Part of keeping your outboard engine running smoothly and reliably involves some annual maintenance. Proper maintenance on your outboard saves you money down the road in costly repairs. So does winterizing your boat and its engine for extended periods of storage. 

Watch the video above and read on below for our checklist of what you should do for the annual maintenance service known as the 100-hour service, as well as our checklist for the winterization process of an outboard engine. 

What is 100-Hour Service?

The 100-hour annual outboard maintenance is a more in-depth inspection and service than simple routine maintenance. It should be done after every 100 hours of use or at least once per year. However, if you use your boat year-round, you should run through the 100-hour annual maintenance service checklist below at least twice per year.

1 - Change the Engine Oil (4-stroke)

Like most engines, outboards need oil changes too. Drain the oil from your outboard motor and replace it with new oil. Refer to your outboard manufacturer's recommendations for what type of oil to use. Watch the video below to see how to change the oil in a 4-stroke outboard engine. 

2 - Change the Lower Unit Oil

Just like the engine oil, the lower unit or gearcase oil needs to be changed out. Drain and replace your outboard’s lower unit gearcase oil, again using the manufacturer's recommendation for which type of oil to use. Watch the video below to see how to change the gearcase oil in an outboard motor.

3 - Replace the Spark Plugs

Spark plugs are a cheap and easy part to replace on your outboard. A bad spark plug can leave you stranded out on the water, so make sure to change them all out. Watch the video below to see how to change the spark plugs on an outboard engine. 

4 - Replace the Water Pump Impeller

Water pump impellers are another cheap and easy outboard part to replace. Changing the impeller once a year helps keep your water pump from failing. While replacing the impeller, check the water pump canister, and the lower plate or housing for wear or damage, and replace them if necessary.  Watch the video below to see how to find and replace the water pump impeller in an outboard motor.

5 - Replace the Thermostat

The thermostat can’t be serviced or repaired, so it should be replaced with a new one and the old one should be discarded. Thermostats don’t usually need to be replaced every year, but check with your outboard’s owner’s manual for how often the thermostats need to be replaced, and make it part of the annual service if it’s time to change it out. 

6 - Inspect Propellers

Check the propellers for damage. While minor abrasions and blemishes can be removed with a file, a propeller needs to be replaced if it has any serious dents or deformities on the blades. 

7 - Grease the Fittings

Use marine grease to coat any grease fittings (or zerk fittings) on the trim-and-tilt mechanism and steering mechanism.

8 - Cooling System

Flush the cooling system for several minutes with fresh water. Salt, sand and silt cause blockages in the engine, so if your outboard runs in salt water, flush the cooling system with a salt remover formula to remove any salt deposits before flushing it with fresh water.

9 - Engine Leakdown Test

A leakdown test is a good indicator of the overall health of an outboard engine, and doing this test once a year can help you check if it’s in peak condition. Watch the video below to see how to do a leakdown test on an outboard motor. 

Winterization Process Checklist

Next on our checklist is the winterization process, which is preparing your outboard for extended periods of inactivity, such as storing it away for the winter. 

1 - Flush the Cooling System

Do a cooling system flush with fresh water. If your outboard has been exposed to salt water, flush it with salt remover, and then with fresh water for at least 10 minutes. Finally, flush it and fill it with a marine anti-freeze, which prevents any liquid left in the cooling system from freezing or damaging the outboard during the winter. 

2 - Change the Engine Oil (4-Stroke)

Drain and replace the engine oil before storing away your outboard. Even if you recently changed out the motor oil, tiny contaminants in used oil can corrode the engine, so replacing the oil should always be done as part of the winterization process. Watch the video below to see how to change the oil in a Yamaha outboard engine.

3 - Change the Lower Unit Oil

The lower unit or gearcase oil should be changed for the same reasons you should change the engine oil, specifically to prevent contaminants in the used lower unit oil from corroding the inside of the gearcase. Watch the video below to learn how to change the gearcase oil on a Yamaha outboard.

4 - Add a Fuel System Stabilizer

Adding a fuel stabilizer to the fuel system helps keep it fresh throughout the storage period. After adding the fuel stabilizer, run the engine for a few minutes to make sure the stabilized fuel runs through all the fuel lines and into the carburetors or fuel rails. 

5 - Fog the Cylinders

Fogging oil protects the inside of the cylinders and piston heads against corrosion. Remove the spark plugs, and spray fogging oil directly into the cylinders, then reinstall the plugs. 

PRO TIP: Now would be a great time to replace the spark plugs with new ones.

6 - Protect the Powerhead

Coat the outside of the powerhead with a thin film of corrosion guard to prevent corrosion from forming on and damaging it during the period of inactivity. Watch the video below to see how to winterize a 2-stroke outboard motor.

7 - Charge the Battery

Your outboard’s battery should be removed from the motor and preserved with a smart charger such as the battery tender, which maintains the battery’s power level healthy during the winter storage period. 

8 - Grease the Propeller 

Use marine grease to lightly coat the propeller and the prop shaft, which helps prevent rust and other forms of corrosion. Watch the video below to learn how to protect an outboard engine from corrosion.

9 - Wash the Engine Cowling

Give the engine cowling a good wash, and apply a couple of coats of marine wax to it. 

PRO TIP: This would also be the perfect time to touch up blemishes on the cowling and replace any faded or missing decals as well. 

10 - Cover your Outboard

Finally, put an engine cover over your outboard motor to prevent moisture and ice from forming on it during the winter storage period. 

Don’t put off performing the annual 100-hour service for your outboard when it's due, and don’t cut corners on the winterization process. Bookmark this page and run through these checklists whenever the time comes around again to do the annual maintenance or winterization of your outboard.