15 Outboard Motor Maintenance Blind Spots You Can’t Afford to Miss

It’s that time of year again. I don’t know about you, but it’s hard for me to make the time to put away my outboard motor for the winter properly. There always seems to be a dozen other chores of higher priority at the same time. Besides winterizing Summer Dance, there’s the camper to winterize too, the yard and garden to prepare, and other fair weather projects to wrap up.

It’s tempting to just store the outboard as-is and deal with it in the spring. Or to just do the minimum maintenance and turn a blind eye to the others. Procrastinating is so easy. But I know life will be just as hectic in the spring if not more so. Either I’ll forget to do those other maintenance tasks altogether or the guilt of knowing the condition I left my motor in will haunt me. So I may as well roll up my sleeves and do it. I’ll be glad I did.

Before I go any farther, a bit of legal housekeeping. This post contains affiliate links. That means I receive a small commission if you make a purchase using these links. Those commissions help to pay the costs associated with running this site so that it stays free for everyone to enjoy. For a complete explanation of why I’m telling you this and how you can support this blog without paying more, please read my full disclosure.

Maintaining your outboard motor properly is the only way to get the best performance and the longest life out of it. It makes the difference between having a motor that you call Old Faithful and one you call Old Faithless, meaning you have no faith that it will start and run every time you need it to.

With proper maintenance, your motor can take routine use in stride and even surprise you when the unexpected happens. That was the case with the outboard that the folks at Yamaha named Old Crusty. It sank while attached to its sailboat during Hurricane Andrew in 1992 and laid underwater for 5 months. It started on the third pull.

What follows is the checklist I use when I service and store my outboard, a 2004 Yamaha 8 HP long shaft. I really like it, not only because it’s reliable, strong, and quiet, but it also charges the house battery on Summer Dance. Along with some basic pointers, I’ve added some tips that some of you veteran skippers might not have considered before.

This post is not a how-to-do-it guide. It’s a what-to-do guide. And this list is not the only or last word on maintaining your outboard. Always follow your engine’s owner’s manual to the letter to do these tasks, avoid problems, and keep your warranty valid.

Blind spot #1 – Motor oil

Okay, I’m starting off with the easy one. Make sure there’s enough oil in the crankcase. Everybody knows that, right? Well, think about it. If it were such a no-brainer, why do some outboard motors have low oil pressure warning lights on them? Because we forget. Heck, I forget to check it sometimes. Make it a habit to check the oil level before you start the engine for the first time each outing. To help you remember, put a rubber band or a red velcro strap on your starter handle.

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Do you change the oil every 100 hours or six months, whichever comes first? It’s probably less than a quart. You can easily afford to change it often. How about when you change it? Do you change it at the end of the sailing season and then let it sit for the winter, possibly gathering condensed moisture, especially in high humidity regions?

Tip

It’s better to change it at the beginning of the season to flush out anything that may have collected in the crankcase over the winter (including fogging oil #11) and to start the season with guaranteed fresh oil. If you only want the best oil for your outboard, use the most current American Petroleum Institute (API) service category, SN.

Blind spot #2 – Lower unit oil

The lower unit of your outboard is the equivalent of the transmission in your car. People who have had transmission failures often neglected to change their transmission fluid regularly. My wife’s car has almost 300,000 miles on the original engine and transmission. I believe that’s partly due to my changing half the transmission fluid every year and the filter every other year. It doesn’t need an expensive flush and it keeps consistently (although not entirely) clean fluid in it over the years.

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The lower unit of your outboard motor is a pinion gear drive mechanism that is very expensive to repair or replace. Your lower unit probably holds less than a cup of gear oil. Change it at the recommended interval, which is probably the same as the motor oil. It doesn’t hurt to check it periodically during the season either.

Tip

Besides checking the level with the upper plug, also drain a teaspoon or so from the lower plug and check its color, especially if you keep your boat in a slip for long periods with the motor lowered into the water. Milky looking oil is a sign that you have water leaking into the lower unit due to a faulty seal.

Blind spot #3 – Gasoline quality

What kind of gas do you run in your outboard, the same as you put in your car, regular grade? Your dad probably ran regular grade gas in his outboard with no problems. Back in the day, the octane rating of regular gasoline was higher than it is today with the addition of ethanol to help lower emissions. Ethanol is particularly bad for outboard motors because it absorbs water. That means gas that sits in your fuel tank for a long time can carry corrosive moisture through your fuel system, damage the carburetor, cause starting problems and poor performance.

A recent Practical Sailor report states:

Studies by BoatUS and the EPA have shown that anywhere between 5 to 20 percent of the contents of a portable or installed polyethylene tank can vanish during the course of a year, the result of breathing losses and permeation. The remaining fuel is lower in octane, contains fewer of the volatiles that are so essential for easy starting, and has reduced solvency for gum and varnish. It often looks perfectly good—most of our samples did—but is perfectly rotten and potentially harmful as fuel.

Beware of moisture-absorbing ethanol

Always use ethanol-free fuel. It’s often sold as the premium grade gas at stations that cater to boaters. For an interactive map of gas stations near you or on the way to your cruising grounds that sell ethanol-free gasoline, visit pure-gas.org. If methanol is used as an additive in your area, check your owner’s manual for the manufacturer’s specific recommendation.

Tip

Don’t run stale fuel in your outboard. If your fuel tank will sit unused with gas in it over the winter, add a fuel stabilizer such as Sta-Bil or better yet burn it in your car or lawn mower. Only burn fresh fuel in your outboard and close your fuel tank vent when it’s not in use to minimize evaporation and exposure to moisture.

Blind spot #4 – Cooling system

Your outboard motor relies exclusively on its water cooling system to keep the engine at safe operating temperatures. It’s not air-cooled like most other small engines you’re familiar with so if its cooling system fails, overheating and permanent damage are very likely to occur.

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Fortunately, the system is very simple. A small pump pulls water from near the propeller, circulates it through cooling passages in the engine where it absorbs combustion heat, and expels it out of the motor. Barring pump failure (more on that in a minute), the system will work fine unless the water passages get clogged, which can happen from salt deposits or debris getting sucked into the engine.

You can help prevent cooling system clogging by flushing the cooling system regularly with clean, fresh water. Some motors have a special connection for this purpose. Older motors need an accessory flushing device.

Tip

Flush your motor’s cooling system after each use if you sail in salt, muddy, brackish, or contaminated waters. Flush it regularly even if you sail in fresh water.

Blind spot #5 – Fuel system

So you’ve got fresh, ethanol-free gasoline in your tank. You’re good to go, right? Maybe not. That fresh gas is only good if it makes it to the carburetor and doesn’t pick up any contaminants along the way.

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Inspect your entire fuel system from the tank to the carburetor annually:

  • Drain and clean your fuel tank
  • Inspect the tank seals and fittings for leaks
  • Check the fuel lines for cracks and loose clamps
  • Test the primer bulb for proper operation
  • Replace the fuel filter and any suspicious parts

An outboard motor that is difficult or fails to start and run smoothly can ruin your day and destroy your trust in your sailboat’s most valuable piece of gear

Tip

Carry a spare fuel filter onboard in case you get some dirty gas or have unexpected motor trouble.

Blind spot #6 – Spark plugs

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Your outboard’s spark plugs are one of its most susceptible parts to failure, especially for two-cycle motors. Fouled or deteriorated anodes can fail unexpectedly and at the worst possible time. Remove, clean, inspect, and adjust the gap of each plug at least annually. Replace them annually for worry-free motor sailing. While you’re at it is a good time to also check the idle speed.

Tip

Keep a spare set of plugs onboard just in case. A spare starter rope is a good idea too. You never know when you or a fellow boater might need one.

Blind spot #7 – Water pump

The water pump in your outboard motor is the heart of its cooling system as I described above. It’s so important that it deserves its own talking point.

The part of your water pump that requires the most maintenance is a flexible rubber impeller. It’s driven directly by the motor’s output shaft similar to the propeller. The impeller is inside of the shaft housing on top of the lower unit. As the impeller rotates, it pulls cold outside water into the pump housing and pushes it up to the motor where it circulates and exits. The impeller’s flexible rubber vanes must make a water-tight seal against the inside of the water pump for it to work properly.

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An impeller should give you years of service if you don’t run the engine for long periods daily and if you flush the system regularly. If the vanes wear out due to friction, water flow through the motor will gradually decrease until overheating begins. Since they are made of rubber and sailors don’t run their motors as often or as long as power boaters, the impellers of sailboat engines eventually dry out and begin to crack.

If they crack enough, vanes will begin to break off and water flow will immediately and dramatically decrease. The broken pieces can also lodge in your motor’s cooling passages. Sailboat impellers often time out before they wear out. For that reason, you want to replace your impeller before it fails so that you don’t risk sudden, unexpected engine damage. The only way to know if your impeller is showing signs of wear or age is to inspect it annually.

Inspecting and replacing an impeller isn’t difficult if you’re experienced with working on motors or you’re adventurous. But the job is beyond the scope of this post so I wrote a separate post, How to Rebuild an Outboard Motor Water Pump. It includes a video that walks you through the job and shows another casualty of galvanic corrosion.

Replacing your outboard motor impeller violates the rule “If it ain’t broke, don’t fix it” but along with the other maintenance points in this post it helps your outboard to live a long, healthy life.

Tip

Consider installing an optional, chromium-plated water pump kit if one is available for your motor and you run your motor in muddy waters.

Blind spot #8 – Control cables

If you’ve ever watched a good airplane pilot during take-off, before they rev the engines and launch down the runway, you might have noticed that they test the plane’s flaps, elevators, and rudder fully. It’s a pre-flight check to be sure the plane’s control surfaces function smoothly and completely. They know that during take-off is a bad time to find out that something’s stuck.

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Your sailboat has similar controls for the rudder and sails. You should think of your outboard motor’s control cables that way too. When properly maintained, they help your throttle and transmission to work smoothly and reliably. If neglected, they can make a smooth running engine temperamental to control and a transmission unpredictable to shift, both things that you don’t want when you’re doing intricate docking maneuvers.

Fortunately, maintaining those control cables takes minimal time and effort. If you’re a lifelong DIYer and you ever owned a bicycle with a front brake or a motorcycle, you should know how to lubricate control cables. The principle is the same for outboard motor cables: get lubricant inside the cable sheath for the length of the cable.

The easiest way to do that is:

  1. Disconnect the upper end of the cable.
  2. Elevate it as much as possible.
  3. Drip or spray lubricant into the cable opening.
  4. Wait for gravity or pressure to distribute it through the cable.
  5. When it begins to come out the other end, reconnect the loose end and clean up any excess.

Depending on the type of cables on your motor, you might also be able to use a cable oiler to inject oil into the cable without disconnecting it. Do that every couple hundred hours and your cables will be trouble-free.

Tip

While you’re at it is a good time to also grease the throttle and transmission control links on both ends of the cables and to check your throttle friction adjustment.

Blind spot #9 – Sacrificial anodes

Your sailboat might have a sacrificial anode attached to its metal keel or to the hull. It provides a path of least resistance for electrolysis to eat instead of your keel. That way, you won’t need to refinish the keel as often.

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Your outboard probably has sacrificial anodes attached to it too because it is electrically isolated from your keel anode by your fiberglass hull and in case your boat doesn’t have its own anode. Your motor needs protection either way or its many expensive aluminum parts will corrode rapidly, especially in salt water.

Consult your owner’s manual for the locations of all anodes on your motor. There is usually one anode attached to the lower unit below the water line.

Sacrificial anode in the water jacket of the engine block

There may also be one attached to the engine block as well. Look for one bolt head that is different than the others and doesn’t appear to attach anything to the engine.

Inspect the anodes every three months if your motor lives on the water or annually if you dry sail. Remove any loose scales and replace anodes that are badly corroded.

Tip

Don’t paint over any anode, even on your keel, or you will defeat its purpose. Repair or replace any damaged or broken ground leads on your motor. If you don’t, parts of your motor may not be protected by the anodes.

Blind spot #10 – Propeller

This one might seem like a no-brainer. Inspect your propeller occasionally for bent or chipped blades, especially after you accidentally hit something with it. But there’s more to watch out for or, to be more precise, it’s what might not be obvious that you should look for.

It’s a good idea to remove your propeller periodically if for no other reason than to make sure there isn’t fishing line or weeds wound around the shaft. Any foreign objects wound next to the oil seal can cause heat buildup that can lead to seal failure and the lower unit oil to leak out or water to leak in.

Follow your owner’s manual instructions to remove the propeller (and spacer, if applicable), inspect the shaft, splines, and seal. Tighten the propeller nut to the recommended specifications and always replace the cotter pin.

If the finish on your propeller is worn or damaged, see How to Refinish Your Aluminum Propeller.

Tip

To help you loosen and tighten the propeller nut, block the propeller with a piece of wood between the blades and the cavitation plate like in the picture above.

Blind spot #11 – Fogging oil

Before you store your outboard for the winter, spray fogging oil into the cylinders to prevent corrosion and a dry startup in the spring.

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Remove the spark plugs, spray fogging oil into the cylinders as directed in your owner’s manual or on the oil can (typically 10 seconds), pull the starter rope to cycle the pistons a couple of times to distribute the oil, and then replace the spark plugs. I also cycle the pistons periodically over the winter to redistribute the oil. Monthly is a good interval since that’s the same frequency that I reconnect my battery charger to top off the house battery.

When you prepare and test it before your first outing in the spring, the motor will smoke considerably for a minute or two as it burns off the fogging oil but that’s normal. It should run normally afterward.

Blind spot #12 – Corrosion prevention

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One sign of an aged outboard motor that has been well maintained is that there is little or no rust or corrosion on the outside of the engine. It’s clean and the wires, hoses, and plastic parts aren’t dried out, brittle, and cracked. Assuming the motor was actually used and not in storage most of its life, there’s a good chance the owner sprayed the engine exterior with silicone spray after they cleaned it with soapy water and dried it thoroughly.

Silicone spray forms a waterproof barrier between engine parts and the moisture that seeks to destroy them. It’s quick and easy to apply and prevents the corrosion that turns good motors into good anchors.

Blind spot #13 – Grease fittings

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Besides the motor oil and gear oil, your outboard might have grease fittings that need regular refilling. These are typically at the main swivel joint between the transom clamping assembly and the main motor assembly.

Other common points that need grease applied by hand are the clamp screws, tilt lock mechanism, throttle linkage, shift linkage, choke linkage, and propeller splines. Apply a high-quality marine grease and wipe off any excess.

Blind spot #14 – Run dry

Anytime you won’t be running your outboard motor for more than a week, it’s a good idea to run it completely out of fuel rather than let the fuel grow stale, hold moisture, and build up varnish in the fuel lines and the carburetor.

Simply disconnect the fuel hose from the engine while it is idling at the end of the day. When the engine finally dies, the fuel system will be dry and ready for short-term or long-term storage. Be sure to prime the system completely with the primer bulb before you start it next.

Blind spot #15 – Storage orientation

If you must lay your motor on its side over the winter, check your owner’s manual for the correct storage orientation. Some motors can drain crankcase oil into the cylinders if laid horizontally on the wrong side. The excess oil can prevent the engine from starting or cause engine damage.

Tip

You can make a motor stand like this one to store your outboard vertically and make it easier to move and work on.


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12 Comments Add yours

  1. Tom Luque says:

    Besides changing oil when it shows signs of discoloration or before long trips, I prefer to change oil before long layups because the oil picks up combustion acids and particulents that will corode engine if left sitting.
    I also use spare engine & fuel tank parts to help drain gas from the fuel line and its squeeze bulb for long layups.

  2. capnrehab says:

    Excellent tips. I’ll be referring back to this post for sure!

  3. capnrehab says:

    As promised, I’m referring back to this post. In tip #2, you mention ” if you keep your boat in a slip for long periods with the motor lowered into the water”. I know you trailer, but I’ll be keeping mine in a slip. Is it better to keep it lowered, or up and out of the water?

  4. If I ever get the chance to leave my boat in a slip, I’ll raise the motor when I’m not using it. Besides minimizing the growies inside the cooling passages, it’ll minimize them on the prop, which can wreck its performance.

    You can paint your prop with anti-fouling paint but that’s yet another maintenance chore. And if you ever need to refinish your prop it’s not easy, especially if it’s aluminum, which most outboard props are. I’m refinishing mine now because of chips, so I’ll probably have a post about it in the spring.

    Keeping it out of the water as much as possible delays or prevents all that.

  5. A somewhat related thought that’s even more dangerous…

    A friend of mine had his nearly new outboard stolen out of his marina a couple weeks ago. Just another in a rash of thefts I’ve heard about this season. It seems to be a popular pastime of the criminals in our midst who need extra Christmas cash. Millions of dollars worth of highly desirable motors get left at slips unmonitored over the winter.

    A lock on the clamps isn’t enough. At least it wasn’t for my friend. They simply unbolted half his motor mount and took it with the motor. A lock cable isn’t enough either. Bolt cutters are cheap and effective. A secure entrance to the marina isn’t enough. Any scumbag with a rowboat can get in under darkness, float right up to your motor and row away with it in minutes.

    The only relatively safe place is stored in your garage until next season.

  6. It is a really good tip to flush out the old oil and replace it at the beginning of each season. I’m looking into purchasing a boat this year, so I want to be sure to take good care of it. It seems like the motor is the only part that really requires a lot of maintenance, so I appreciate your advice on all the commonly missed spots to check for.

  7. Capri 18 in South Florida says:

    Great post. I was looking for the plans to make the motor stand, but the link is not working… the same thing happens when I clicked on the link within the ‘How to Secure Your Outboard Motor for Safe Trailering’ article. Can you repost it, please?
    Thank you!

    1. I’m currently updating that particular post and it will be be live again this weekend, including a link to the plans, so please check it on Saturday.

  8. Capri 18 in South Florida says:

    When is it time to replace vs. repair? I have a 1976 Mercury 110 (9.9hp) for my Capri 18 project boat. I have never run the engine and the shop I brought it to said it has spark and compression (good) but needs about $600-$800 of work (bad). Should I be $tingy and spend that, or should I buy a new one?
    Has anyone switched to propane power (Lehr)? I am intrigued but have read negative feedback on the Chinese made engines.
    Thank you!

    1. In my opinion, you should RUN as fast as you can away from that shop and any other that recommends you invest that kind of money in a 40 year old motor. You should have no trouble buying a late model used outboard for about that amount that is smaller, lighter, and more reliable, especially in Florida. Look in your local craigslist ads. And for an 18′ sailboat, you can probably get by with half the horsepower of your current motor.

      I don’t know anybody with propane motors but I’ve seen a few switch over to electric motors like in Report – Two Seasons With a Torqeedo Outboard.

      1. Capri 18 in South Florida says:

        Thank you. I am not sure if I would buy used if I changed the motor, so the cost difference would be more significant.
        As far as horse power, would I loose torque by going smaller? I am not concerned with speed but ability to re-enter the inlet with an outgoing tide. I’d like to go smaller (and lighter) if I can… of course my power boating friends are always in favor of more hp!

      2. Generally speaking, torque does go down in proportion to horsepower but some motors produce more torque for a given horsepower than others. It also depends on the propeller design. Some are designed for speed, others for torque.

        You have 10 HP motor now for an 18′ boat. I have an 8 HP motor for my heavier per foot 22 foot long boat and it’s more than enough. Use the recommended motor size from Catalina Yachts as a rule of thumb. You would probably be happy with 4-6 HP.

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