To­day’s out­board en­gines grant an­glers the free­dom to fish far from port with great re­li­a­bil­ity and peace of mind. Reg­u­lar main­te­nance en­sures that out­boards con­tinue to per­form well and last as long as pos­si­ble in the salt­wa­ter en­vi­ron­ment.

Some chores, such as chang­ing a wa­ter pump or ad­just­ing valves, might re­quire the skills of a marine me­chanic. Yet other tasks are rel­a­tively sim­ple, re­quir­ing just a few tools, some spare time and a mod­icum of do-ity­our­self me­chan­i­cal abil­ity. Let’s look at what you can eas­ily han­dle on your own.


Us­ing a flush-muff de­vice is an ef­fec­tive way to rinse salt from the in­ter­nal cool­ing­wa­ter pas­sages when the boat is on a trailer. Check your owner’s man­ual for any spe­cial pro­ce­dures, but in gen­eral terms, tilt the out­board down and slide the rub­ber cups of the de­vice around the lower unit to cover the raw-wa­ter in­lets on both sides.

Con­nect a fresh­wa­ter gar­den hose to the flush-muff fit­ting and turn the faucet on un­til you see wa­ter squirt­ing out of both cups. Then start the out­board, mak­ing sure it stays in neu­tral, and run it for about 15 min­utes.

Us­ing an out­board’s builtin flush fit­ting works well on boats kept in the wa­ter. Again, check your man­ual for specifics to your engine. Gen­er­ally speak­ing, im­me­di­ately af­ter you shut down the engine at the dock (this en­sures that the engine is still warm) and with the out­board tilted up, con­nect a fresh­wa­ter gar­den hose to the flush fit­ting, turn the spigot on full blast and let it run for about 15 min­utes. Do not turn the engine on dur­ing this process be­cause wa­ter only trick­les down to the wa­ter pump. You can dam­age the pump’s im­peller while run­ning the engine with this flush method.


Fresh oil is the key to ex­tend­ing the life of a fourstroke out­board. (Two-stroke out­boards do not re­quire oil changes be­cause they au­to­mat­i­cally mix two-stroke oil with the fuel.)

Most oil changes oc­cur at 100-hour in­ter­vals and should also in­clude an oil­fil­ter change. With the boat out of the wa­ter, warm up the engine us­ing a flush-muff de­vice. Re­move the drain plug (check your man­ual for the lo­ca­tion) and catch the used oil in a drain pan. Re­move the oil fil­ter with a fil­ter wrench and re­place it with a fresh one. Handtighten only. Re­place the drain plug.

Find the fill cap for the engine oil (re­fer to your man­ual; the cap is of­ten yel­low in color) and fill the crank­case with the man­u­fac­turer’s spec­i­fied vis­cos­ity grade (aka weight) oil. This is usu­ally a mul­ti­vis­cos­ity oil, such as 10W-40. The man­ual might spec­ify use of a syn­thetic or syn­thetic blend ver­sus a straight min­eral-based

oil. Us­ing the same brand of oil as the out­board (e.g., Ya­malube marine engine oil for Yamaha out­boards) is a good idea be­cause the man­u­fac­turer has a vested in­ter­est in mak­ing sure your engine per­forms well and doesn’t come back for war­ranty re­pairs.

No mat­ter what brand of oil you use for your four-stroke out­board, make sure it bears an FC-W rat­ing. This means the oil has been cer­ti­fied by the Na­tional Marine Man­u­fac­tur­ers As­so­ci­a­tion to con­tain spe­cial ad­di­tives that en­hance lu­bri­ca­tion and in­hibit cor­ro­sion in marine ap­pli­ca­tions.

Most large out­boards re­quire around 5 to 8 quarts of oil. Check your man­ual to be sure. Also, avoid over­fill­ing the crank­case with oil. A quart in ex­cess of the ca­pac­ity can be worse than a quart un­der be­cause the ad­di­tional pres­sure of too much oil can dam­age engine seals and cre­ate leaks. Check the dip­stick (re­fer to the man­ual for the lo­ca­tion) to make sure the crank­case is filled to the proper level.


Rou­tinely chang­ing the gear lube helps you de­tect wa­ter that might be leak­ing into the gear case. The rec­om­mended ser­vice in­ter­val is usu­ally the same as with engine oil. Use the lube spec­i­fied in your owner’s man­ual, such as SAE 90 hy­poid gear oil. To drain the gear case, re­move the drain plug from the bot­tom of the lower unit, then re­move the vent plug just be­low the an­tiven­ti­la­tion plate.

Leave both plugs out and fill the gear case us­ing a hand pump (avail­able at most boat deal­ers and auto-parts stores) with the hose fit­ted to the drain hole at the bot­tom. While fill­ing, give the prop a spin or two with your hand to help purge air from in­side.

Pump in lube un­til it be­gins to spill from the vent. With the pump line still in po­si­tion, re­place the vent plug. Then re­move the pump line and quickly re­place the drain plug.


Use a grease gun to pump marine grease into the zerk fit­tings out­lined in the man­ual at the rec­om­mended in­ter­vals. Zerk fit­tings are usu­ally found on the out­board’s pivot tube (on which the engine ro­tates when it turns), steer­ing tube and tilt-and-trim bracket.


A sep­a­rate 10-mi­cron wa­ter-sep­a­rat­ing fuel fil­ter serves as the first line of de­fense in keep­ing wa­ter and dirt from get­ting to the engine. That’s why it’s im­por­tant to change fuel fil­ters per the man­u­fac­turer’s main­te­nance sched­ule. Yamaha, for ex­am­ple, rec­om­mends re­place­ment ev­ery 50 hours, with the pri­mary and in-line fil­ters re­placed ev­ery 100 hours.


Af­ter ev­ery trip, man­u­ally spin the pro­pel­ler. If there’s fish­ing line wrapped on the prop shaft, you can some­times hear a soft tick, tick, tick — the re­sult of a piece of monofil­a­ment or fluoro­car­bon fish­ing line slap­ping the in­side prop bar­rel.

Braided line is too limp to cre­ate the same sound ef­fect, so you still need to re­move the prop to in­spect the shaft for a tan­gle of line and pos­si­ble dam­age to the gear-case seal. Do this ev­ery other trip. If you find fluid leak­ing, take the mo­tor to a shop to in­spect the gear case and re­place the seal.

Be­fore re­in­stalling the pro­pel­ler, be sure to lu­bri­cate the shaft, thrust bear­ing, prop nut and other hard­ware with marine grease to make it easy to re­move ev­ery­thing next time around.


Pe­ri­od­i­cally in­spect the sac­ri­fi­cial zinc an­odes on your out­board. These in­ten­tion­ally cor­rode be­fore your out­board does in or­der to pro­tect the mo­tor. Re­place them when they are 50 per­cent gone.


The ser­vice in­ter­val for chang­ing spark plugs is gen­er­ally around 200 hours. Buy the right plugs, and “gap” them cor­rectly. The gap be­tween the cen­ter and ground elec­trodes will be spec­i­fied in the man­ual; use a feeler gauge to con­firm that proper gap.

Spark plugs are of­ten set deep in the cylin­der head, with in­di­vid­ual coils (con­nected to the plug wires) bolted over each one. Un­bolt the coil and then care­fully pull the boot off of the plug. Then use a deep spark-plug wrench (of­ten sup­plied in the out­board tool kit) to un­screw and re­move the plug.

Us­ing the plug wrench, in­sert and thread the new plug into place (be care­ful not to cross-thread it) and tighten snug­gly. Don’t over­tighten, which can strip the threads in the alu­minum head. Snap the boot back on and reat­tach the coil. Re­plac­ing the plugs one at a time helps you keep track of where each coil and plug wire goes.


Pe­ri­od­i­cally treat­ing the pow­er­head with cor­ro­sion-in­hibit­ing spray lends the mo­tor pro­tec­tion from er­rant salt spray un­der the hood. Use a cor­ro­sion in­hibitor spec­i­fied by the man­u­fac­turer. Mer­cury Marine, for ex­am­ple, rec­om­mends Quick­sil­ver Cor­ro­sion Guard (about $8 for an 11-ounce aerosol can).

The do-it-your­self route might not be for ev­ery­one. Even if you have a marine me­chanic han­dle ser­vice, it’s im­por­tant to know what’s re­quired and why. No mat­ter how you go about out­board main­te­nance, think of it as your ticket to stay­ing on the wa­ter and catch­ing fish.

Check the engine oil level be­fore each trip. When re­fill­ing, pour in the proper amount and no more. Ex­cess oil can dam­age oil seals and cre­ate leaks.

Us­ing the same brand of oil as the out­board, in this case, Suzuki Marine Ec­star oil, is a good idea be­cause the builder has a vested in­ter­est in mak­ing sure the engine runs well.

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