Boat Engine Maintenance and Tips

Boat Engine Maintenance and Tips

For the better part of a decade, the old ten-horse outboard hanging on the back of the jonboat shared by a buddy and I seemed to thrive on neglect. Pretty sure we never checked the spark plugs or changed lower unit oil or replaced fuel filters or any other basic bit of outboard engine maintenance. When the lower unit sprang a crack, we simply gave it a rough weld job and threw her back in the drink. Problem solved.

That theory lasted until the day my buddy and I found ourselves stranded five miles downriver, the sound and smell of grinding metal finally driving home a rather important point about boat motor maintenance. As in, taking care of your engine isn't just one possible course of action—but the only way to roll on the river.

Like my buddy and I, you might still run a vintage 2-cycle outboard on the back of your fishing ride; or maybe it's a stealthy new 200-HP 4-stroke rigged to the transom of your bass boat. In all cases, caring for your on-water transportation assures your mind remains focused on catching fish, as opposed to fixating on some weird sound emanating from your lower unit.

Fuel First

Gasoline and proper care for your motor's fuel system remains the easiest way to keep running smoothly. Honda Marine recommends that when you pull up to the gas pump, avoid fuel containing more than 10-percent ethanol. Gas containing higher levels of ethanol is corrosive and attracts water, which can cause starting or running problems—eventually damaging your engine's fuel system.

Boat Engine Maintenence

Consider, too, that E85 is an alternative fuel containing 85% ethanol and 15-percent gasoline. Technically, it is not even gasoline. And most outboard engines are simply not designed to run E85 or other alternative fuels. Relative to different octane ratings, many engine manufacturers recommend basic 87-octane. However, in many regions, 91-octane is the only fuel containing less than 10-percent ethanol.

Beyond basic fuel rules, many mechanics recommend replacing the inline fuel filter every year for top performance. In regions where avoiding ethanol laced fuels is problematic, it may also be wise to install a second, water-separating fuel filter.

If your fuel's been sitting unused for more than a month, check or ask your mechanic to check a small fuel sample, looking for the presence of water or debris. Water will separate from fuel and appear as a clear liquid at the bottom or a container. That's a bad sign.

In very warm, high humidity regions, fuel can deteriorate and oxidize in as little as 15 days. Even if you routinely run through a full tank of gas within a week, it's always beneficial to pour a can of fuel additive into the gas tank.

Sta-Bil 360 Marine Ethanol Treatment guards specifically against condensation, cleaning the fuel system and stabilizing fuel for up to 12 months. Treat at a rate of one ounce per ten gallons of gas at every fill up. Sea Foam is another fuel stabilizing additive that cleans injectors and carburetors, controls moisture and reduces gum and varnish deposits. One 16-ounce can costs about ten-bucks and treats up to 16 gallons of gas. Another additive called Ring Free excels at clearing engine deposits, while combating the corrosive elements of ethanol.

Flushing Fluids

Outside the fuel system, the other first thing your mechanic often does when servicing or winterizing an engine is to flush and refill gear case oil in your engine's lower unit—it's easy enough to do it yourself. Place your outboard in the vertical position, and slide a suitable container below the drain hole to catch the used oil. Remove the lower oil drain hole plug first, followed by the upper oil level plug, which will start the flow of gear case oil. If a large slotted screwdriver won't loosen the plugs, you may need to tap on them with an impact screwdriver and mallet to break the seal.

Boat Engine Maintenance

Once the lower unit is completely drained, inspect the oil for a black or milky color or a burned smell. If so, it's a good idea to let an authorized mechanic inspect your motor. Pour the used oil into an enclosed container and drop it at your local fluid recycling center. Now refill the lower unit with fresh gear case oil, using a gear case oil pump connected to a gear oil bottle and lower oil drain hole on your outboard. Follow your engine manual guidelines for recommendations on suitable gear case oil brands and capacities. Some of the newer engines require a synthetic oil, which is a different weight. Continue filling until oil flows out the top oil level hole. Re-install the oil level plug and tighten. Remove the oil fill pump from the drain hole and re-install the plug.

Regarding your primary engine oil, many of the newer outboards today feature oil injection systems precluding the need to premix your fuel. Top off the oil reservoir at regular intervals, using the highest quality oil recommended by the manufacturer. For 2-cyle outboards, use a premium TC-W3 oil. Four-stroke engines often require a 10W-30, 10W-40 or 35W-40. As with your car, replacing the oil filter and unused oil on an annual basis will always help extend engine life.

The Electrical Stuff

Another necessary and easy practice is to lubricate your engine's grease or zerk fittings. Look for one fitting on the steering rod and two more for the steering cable. Also, visually inspect your shift cable, throttle cable, linkages, electrical connections and hoses for any excessive wear.

From there, move to the spark plugs. First, remove the spark plug wires, one at a time, twisting the cap back and forth to release the seal. Remove the plug with a socket wrench and inspect the base of the plug for excessive wear and scorching. Installing new plugs at least every other year is a wise move. When installing new plugs, apply a dab of Anti-Seize lubricant to the threads so they'll be easy to remove the next time around. Once you've re-installed the spark plug and applied the recommended torque, add a little Boot Protector to lubricate the boot and prevent arching and moisture.

Given your boat's increased power demands, such as large sonar screens, radios and other electronic accessories, make sure you periodically inspect your marine/cranking battery, checking for corrosion or cracked or worn cables. Installing fiber battery washers can help prevent corrosion, while spraying battery posts with a liquid battery terminal protector can further extend battery life. Check the tightness of your wing nuts with a wrench. From there, check for any faulty fuses, making sure your emergency boat kit is stocked with spares of various sizes. While you're doing this, it's always wise to test your bilge pump, as well.

You can check your boat's primary charging system (alternator) by connecting a volt-meter to the battery's terminals. Turn on the ignition key but don't start the engine and note the volt-meter reading (system voltage). Now, start the engine and again note the voltage, which should be at least 1-volt above the previous system voltage. If so, your charging system is functioning normally.

Proper Props

Before hitting the water each year, you'll want to remove and inspect the propeller and clean and lubricate the propeller shaft. Remove the cotter pin and the main prop nut (best to use a prop wrench and a pair of gloves.) Next, remove the thrust washer, and inspect the prop shaft for any damaged seals or fishing line. Apply a quality marine-grade grease to the prop shaft before re-installing the thrust washer, propeller, and nut and pin (carry extras.)

Boat Engine Maintenance

Choosing the right propeller for your engine can make even an experienced boater feel like a greenhorn. First, know that the term pitch refers to the forward distance a propeller travels in one 360-degree revolution. In theory, more pitch means more speed, but your engine must also possess enough power or torque to turn the propeller. If you put too much load on the engine, it won't capable of delivering its maximum horsepower.

Determine your engine manufacturer's recommended RPM is at full, open throttle. Say that figure falls in the 4700 to 5000-RPM range. If the propeller can deliver the recommended RPM range, you'll be getting maximum fuel efficiency and power. If you're running under the recommended RPM range, say at about 4500-RPM, you likely need to choose a propeller with a lower pitch. Every additional inch of pitch decreases RPM by roughly 150, so by dropping down by one or two inches of pitch, you should be able to achieve your target RPM. Most engine manufacturers— recommend a range of different propeller options based on horsepower and model. Start there. Ultimately, exact prop selection should be based on your boating preferencestowing, top end speed, hole shot, or simple fuel efficiency and a smooth ride.

Season's End

When it's finally time to store your rig for the winter, most of the necessary tasks can be done right in your own driveway. If your boat's been in saltwater, start by flushing the lower unit with clean, fresh water. If you regularly run in shallow water with lots of vegetation, sand and debris, flushing your cooling system and impeller is also a good idea. Connect a garden hose to a dual motor flusher (aka "earmuffs), which covers water intakes on either side of your lower unit. Turn on the water, start and run the engine at idle for 5 to 10 minutes to give the engine a thorough flush.

Boat Engine Maintenance

While you're focused on the lower unit, perform a gear case oil flush and fill, as outlined above. Before parking your rig for its winter nap, fill the fuel tank with fresh gasoline and add your preferred stabilizer, usually at a rate of about 1-ounce per gallon. Run the engine at idle speed (leaving in neutral gear) for about 10 minutes to circulate treated gasoline and replace untreated gas throughout the fuel system. When this is done, tilt the motor all the way up and all the way back down to vertical. This assures you've drained all water from the lower unit, which could potentially freeze and cause damage during storage.

Today, many of us have been trained to fog our engines with a quality engine fogger. If you're running a 2-cycle outboard, fogging is still recommended by most mechanics. For 4-stroke motors, however, many experts feel fogging isn't necessary. Some folks suggest starting an unfogged 4-stroke every 3 weeks or so, although if you've done all the above, it generally isn't necessary, so long as you'll be running the boat again within 6 months.

Fully charge all batteries and disconnect battery terminals. Every few weeks, check battery charge status and trickle charge back to 100-percent, as necessary. When spring arrives, your outboard will thank you by starting on the first crank and transporting you to your favorite fishing spots, all season long.

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Recommended Articles

See More Recommendations

Popular Videos

Thomas and Thomas Contact II Fly Rod

Thomas and Thomas Contact II Fly Rod

Joe Goodspeed, rod designer at Thomas & Thomas, tells Fly Fisherman editor Ross Purnell about the six new models of Contact II fly rods, including a 10-foot 2-weight and a 10-foot 3-weight. Constructed from five types of premium carbon and fiberglass fibers bonded by a proprietary aerospace resin, these rods are stronger and yet capable of making, short, delicate casts.

New G. Loomis IMX Pro Rod Series

New G. Loomis IMX Pro Rod Series

David Brinkerhoff of G. Loomis shares his knowledge of the new IMX Pro rod series. The IMX Pro rod series comes in 10 new models and will cover five technique-specific categories. Available Fall 2020. MSRP $345-355.

Rapala OG Slim 6

Rapala OG Slim 6

The 2019 Bassmaster Classic champ Ott Defoe sits down with In-Fisherman Associate Publisher Todd Ceisner, to talk about Rapala's new OG Slim 6 crankbait. The OG Slim 6 will feature a flat-sided, balsa body, and will dive around 6 feet. Featuring a circuit board lip, the OG Slim 6 deflects off of cover better than traditional plastic lips. Offered in 14 colors and available in tackle stores Fall 2020. MSRP $10.99.

Make Your Own Tackle Box with Plano Edge Flex

Make Your Own Tackle Box with Plano Edge Flex

Plano's Charlie Davis and In-Fisherman's Rob Neumann talk about the new Plano Edge Flex as part of the 2020 ICAST New Fishing Gear Guide.

See More Popular Videos

Trending Articles

Check out this Largemouth Bass Length To Weight Conversion Chart, a simple and accurate explanation from the In-Fisherman biologists. Bass

Largemouth Bass Length To Weight Conversion Chart

Dr. Rob Neumann - January 22, 2017

Check out this Largemouth Bass Length To Weight Conversion Chart, a simple and accurate...

Several methods are available to estimate the weight of a fish. Some use length as well as girth measurements. Biology

Walleye Length To Weight Conversion Chart

Dr. Rob Neumann - January 03, 2017

Several methods are available to estimate the weight of a fish. Some use length as well as...

The Pro-V shape of this hook is called a sickle-style hook. Midwest Finesse

Eagle Claw Fishing Tackle's Trokar Tungsten Pro-V Finesse Jig

Ned Kehde - August 13, 2020

The Pro-V shape of this hook is called a sickle-style hook.

You're going to love this Beer-Battered Fish Fingers Recipe! These deep-fried walleye strips are tasty and dress up nicely when served in a basket or on a plate with fresh fruit such as grapes and strawberries. Fish Recipes

Beer-Battered Fish Fingers Recipe


You're going to love this Beer-Battered Fish Fingers Recipe! These deep-fried walleye strips...

See More Trending Articles

More How-To

To guide your carp quest, we've lined up the best carp baits that are easy-to-fish natural baits and commercial options. Carp

10 Best Carp Baits Available Today

Dan Johnson

To guide your carp quest, we've lined up the best carp baits that are easy-to-fish natural...

Soft trailers on the back of jigs, spinnerbaits, bladed jigs, and buzzbaits contribute to a lure's vibration package in important ways. How-To

Adding Softbait Trailers to Bass Lures

Steve Quinn - March 29, 2018

Soft trailers on the back of jigs, spinnerbaits, bladed jigs, and buzzbaits contribute to a...

Catfish are simple creatures that can be caught using the best catfish rigs. Catching them is simply a matter of putting a good bait in the right in front of them. Catfish

8 Best Catfish Rigs - When, Where and How to Use Them


Catfish are simple creatures that can be caught using the best catfish rigs. Catching them is...

Muskie fishing could be described as dull routine, interrupted by chaos, as a thousand things can How-To

Reels for Muskies And Pike

Jim Edlund - August 31, 2017

Muskie fishing could be described as dull routine, interrupted by chaos, as a thousand...

See More How-To

GET THE MAGAZINE Subscribe & Save

Digital Now Included!


Give a Gift   |   Subscriber Services


GET THE NEWSLETTER Join the List and Never Miss a Thing.

Get Digital Access.

All In-Fisherman subscribers now have digital access to their magazine content. This means you have the option to read your magazine on most popular phones and tablets.

To get started, click the link below to visit and learn how to access your digital magazine.

Get Digital Access

Not a Subscriber?
Subscribe Now