Routine Outboard Maintenance

After your engine has been properly run in, you’ll need to establish a maintenance routine that begins with systematic checks every time you use your boat. These checks won’t take long, but could spell the difference between life and death for your engine.

Daily Checks and Outboard Maintenance

Daily checks should include a quick look at just a few key items. First, make sure that your oil tank (if you have one) is topped up. If you have a four-stroke engine, be sure to check the crankcase-oil level and top up if needed. Check your owner’s manual to determine if your dipstick should be screwed in, or left unthreaded when you check the oil level. Failure to do so could give you a false reading, and lead to overfilling or underfilling your engine’s crankcase, which can cause problems.

Check that you have adequate fuel for your intended trip, and that the fuel-tank vent is open.

With the engine tilted up, check for excess oil buildup near your propeller…it could mean that a seal in your lower gearcase has deteriorated. (Note: Some oil film buildup is normal in many cases; look for changes in the amount of buildup. If it appears to be increasing, check the oil level in the lower unit as discussed in the owner’s manual) If the seal has failed, take the engine to an engine repair shop immediately to avoid expensive gear-unit damage.

Check for fishing line wrapped around the propeller hub area. If you ignore it, the line can wrap tightly around the propshaft and cause the aforementioned gearcase seal failure.

If your engine is not through-bolted to the transom of your boat, make sure the screw clamps are tight and secure. Many engines have landed on the bottom of the sea through neglect of this simple check.

Sniff around for any sign of a fuel leak, and if you find one, fix it.

Once the engine is running, make sure to check the “telltale,” or “tracer,” spray, or exhaust discharge, to be certain the water pump is working.

If all these items are in order, you’re ready to go. There’s just one more thing:

If you tow your boat on a trailer, and run it in salt water, flush the cooling system daily with fresh water.

Monthly Checks and Outboard Maintenance

On a monthly basis, besides the routine daily checks, it’s a good idea to remove the engine cover and look for any corrosion build-up near cylinder heads and thermostat housings that could indicate leaky gaskets. Also, look for corrosion at wire terminal connections… clean and tighten them as required and then use one of the proprietary anti-corrosion sprays available at your dealership on all exposed electrical connections and unpainted metal parts of your outboard.

Make sure that throttle and gear-shift controls operate smoothly. Lubricate them as needed. Be aware that you should never shift gears unless your engine is running, so make sure the boat is securely made fast to the dock before checking shift controls for smooth operation.

Next, run the engine with the cover off and check that none of the bolt-on components (fuel pumps, voltage regulators, coils, and the like) have come loose from their mounts. Make sure all wires and cables are securely led and clipped through harness mounts. Next, if your engine is equipped with an engine mounted fuel strainer, check to see if any water has collected in it. It will be easy to see, as the water will separate from the fuel, drop to the bottom of the strainer, and be relatively clear in color compared to the fuel/oil mix above it. If you can see water, remove the strainer housing and drain out the water. Clean the screen element, reinstall, making sure the O-ring is in place before threading the housing back in, and re-check this assembly for fuel leaks after replacing the strainer housing. Simply pump your fuel primer bulb until the filter/strainer fills with fuel, and look for leaking fuel.

Check for corrosion at thermostat housing at top of cylinder head or engine block

Check for corrosion at all wiring connections

Next, you should check the condition of any sacrificial zinc anodes attached to your engine. Check for zincs at the lower portion of the mounting bracket on larger engines. There may be a zinc trim tab behind the propeller, or a small zinc screwed onto the antiventilation plate. Replace any zincs that are more than half eroded. In some areas they can dissolve quite rapidly, and if the zincs are completely gone, the only thing left to dissolve is your engine housing.

Lastly, check your engine’s battery, and top up the cells as needed.

Seasonal Checks and Outboard Maintenance

First let’s define the word “seasonal.” The way I apply it here, it actually means every three months, or every full boating season, whichever comes first. In other words, if you can boat all the year round, or for more than three months anyway, do these checks and maintenance procedures at least once every three months, or about every 50 to 75 hours of operation.

But if you live in a region where your boat use is restricted to less than three months, or 75 hours, consider these “seasonal” checks to be annual checks.

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Three-Month (or Seasonal) Service Checks

Seasonal check-ups are far more comprehensive, and certain operations may require the expertise of your local dealer, but you’ll certainly be able to do all of the work listed here except in a few cases.

Grease Points… All grease points on your engine should be filled with fresh grease as recommended by your manufacturer for the specific engine location. Keep pumping in grease until all the old grease-and any water-is forced out. It’s a messy business, so wipe the old stuff away with a rag as it emerges around the lube point.

Propeller Inspection… First, be certain your ignition system is disabled by disconnecting the spark plug wires at the plugs. Then remove the propeller to inspect the shaft for any fishing line wrapped around it. If you find any, cut it all off.

Inspect the propeller for nicks, burrs, and any unwanted bends in the propeller blades. If the nicks are minor, you can clean them up with a file.

Inspect the propeller hub for any deterioration of the vulcanized rubber and its attachment to the hub spline. Any damage found here could spell trouble next season. If this hub is damaged, you’ll need either to have the prop rehubbed or a new prop. If you’re in doubt, have your dealer make the final call. You certainly don’t want to replace it if you don’t have to.

If all looks okay here, wipe down the propeller shaft to remove the old grease, and apply a thin coat of an approved waterproof grease to the shaft. Don’t reinstall the propeller just yet, as you’re going to run the engine to flush the cooling system, and you should never run an engine out of the water with the propeller on because of the obvious danger from the whirring blades.

When you do reinstall the propeller however, remember to replace the cotter pin for the prop nut if your engine is equipped with one. If your engine uses a Nylock self-locking prop nut, it should be replaced, as these lock effectively only once.

Gearcase-Oil Change… The next step in the seasonal service process is to change the gearcase oil. On most outboards, the gearcase will have two screw plugs evident in the side of the gear housing. Some engines, however, will have the gear unit’s drain and fill screws located on the hub just forward of the propeller, in which case they can only be reached with the propeller removed.

To drain the fluid from your unit, wipe the skeg clean at the very bottom of the engine and attach a piece of masking tape to the skeg.

Get a clean container that’s large enough to hold all the oil in your gearcase and place it under the tape. Remove the lower drain plug. Nothing much will come out until you slowly unscrew the upper check plug. The oil will then leak down the side of the gear housing, down the side of the skeg, and flow straight down the edge of the tape into your drain pan.

Carefully inspect the oil for excessive metal filings or discoloration. If the oil appears milky, or if you noticed a large amount of water coming out of the drain before the oil, then water has somehow migrated into the gearcase, indicating a bad seal.

Clean off the magnetic pickup found on many lower drain plugs and get ready to refill the lower unit with the correct gear oil.

A note of caution here: Don’t let anyone talk you into using straight gear oil as supplied by auto parts stores. Although this oil may have the same distinctive rotten egg odour as the fluid you have just removed from your outboard engine, it may not be the same stuff. Typically, the special outboard engine gear oils have a water-dispersant additive in them that’s not found in the automotive grades. Also, be aware that not all outboards use gear oil in their gearcases. Some use four-stroke engine oil, and others use a fluid quite similar to automotive automatic transmission oil. Be sure to check the specifications for your engine. It’s best to go to your dealer to purchase a container of the correct oil and one of the special fill pumps.

These pumps are quite inexpensive and fit not only the oil container, but screw directly into the threaded lower unit drainplug hole on your engine, minimizing mess. This is an important point, because you’re going to fill the gearcase from the bottom up. Once you are set-up , simply work the pump until you just begin to see oil seeping from the top check-plug hole. Then reinstall the check plug and snug up the screw.

Next, get the drain/fill plug ready to install, wipe down the magnetic pickup, and be sure the sealing Oring or gasket is either in place on the screw plug or in the gear housing. Unscrew the pump tool and quickly insert the drain/fill plug. Tighten it fully. Wipe off any excess oil from the gearcase and watch for leaks. Your oil change is complete.

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Cooling System… The next step in the seasonal service is to thoroughly flush your cooling system with fresh water. A precaution here is to make certain that the flush adapter stays in place while you are flushing the engine. If the adapter slides down on the lower unit to a point below the water inlet, you could burn out the engine’s water pump-or the engine itself-if it’s left unattended for even a brief time.

As part of this cooling system service, it’s also a good idea to remove and clean your engine’s thermostat, if it has one. The internal cavity into which the thermostat and bypass valve fits is a trap for sand, salt, and general debris that gets past the system pickup strainer. With the thermostat removed, clean out any muck you find there and, with the engine running, run fresh water up from the flushing adapter through the engine to this point. You’ll now know for certain that the internal water flow is unrestricted, because water will leak out at this point. Just run the engine long enough to determine that a good solid flow of water is pouring out.

After the thermostat has been cleaned, reinstall it, using new gaskets, and run the engine again to be sure the thermostat cover is not leaking. If your engine has seemed to be running too hot lately, but your inspection has now revealed that water is getting to this point in adequate amounts, the operation of the thermostat could be the problem.

Impeller Replacement. In addition to flushing the cooling system and checking the thermostat, you may also regard the replacement of your water-pump impeller as routine maintenance. To tell the truth, manufacturer’s recommendations vary on this score, some suggesting that you renew the impeller every year, and others that you replace it only as needed. If you regularly venture far offshore, where failure of the water pump could be a serious problem, replace that impeller yearly.

On the other hand, if you use your motor only occasionally throughout the season, or on a tender, for non-risky trips from ship to shore, I’d advise you to replace the impeller every other year.

Cylinder Compression… Now that you’ve run your engine for a bit to flush your cooling system, and have warmed it up, it’s a good idea to perform the annual compression test. Remember, compression is one of your engine’s basic needs and a compression check can often catch impending problems before they become major.

For example, piston rings that are just beginning to gum up will cause low compression before they fail completely. Usually, you can cure this problem by running a manufacturer-approved decarbonizing fluid such as OMC or Mercury “Engine Tuner” through the engine. If you don’t catch this problem in time, the only solution is to take the engine apart. It’s simple to use these engine tuners-the instructions are right there on the product label.

What’s often not so easy is finding out what normal compression is for your engine. Often the specs are not given in the engine owner’s manual or even in the workshop service manual. So it’s a good idea to check the compression when the engine is fairly new and in good running order. Write down the compression figures for each cylinder in your manual for future reference.

As a matter of interest, the actual pressure is not that important-it’s the variation from the norm that you should be concerned with. In the case of a multicylinder engine, start worrying if any one cylinder varies from the others by 15 pounds per square inch (psi) or more. If yours is a single-cylinder engine, a drop of 15 psi from the norm you established when it was new is cause for concern. The steps for performing a compression test are really quite simple, but you must follow them exactly for your own safety and the accuracy of the readings. So be warned-don’t skip any of these steps:

1. First, disable the ignition system by unplugging the gang plug going into your ignition module. If your engine has an emergency shutoff switch, simply remove the lanyard clip to disable the ignition. If neither of these solutions works on your engine, take a wire jumper lead and connect one end to a good engine ground, and the other end to the metal connector inside the spark plug boot. You’ll have to use one jumper for each plug wire. Remember, simply disconnecting all the plug wires may be a dangerous move. Once you remove all your spark plugs and begin cranking over your engine, an explosive fuel/oil mix will be spraying out of the plug holes. A plug wire could spark and ignite this mix outside of the combustion chamber if it isn’t grounded to the engine. Also, this freewheeling type of spark could damage the ignition coils or modules.

2. Remove all the spark plugs, and be sure to keep them in order so you can return them to the cylinders they came from. Carefully inspect the business end of the plugs, looking for any inconsistency in coloration, and for any sign of water or rust near the tip.

3. Next, thread your compression gauge into the #1 spark-plug hole and “zero” the gauge.

4. Open the throttle as far as possible, to ensure that the cylinder gets an unrestricted supply of air. (Some engines allow only minimal opening if the gearshift is in neutral, to guard against over-revving.)

5. Crank over the engine an equal number of times for each cylinder you test, and be sure to re-zero the gauge for each cylinder. If you have

an electric start, count the seconds: “One thousand one, one thousand two, one thousand three, one thousand four” and so on, with the key or start button engaged. This will give you enough cranking time for a usable reading. If you have a pull start, pull the cord four to five times for each cylinder you are testing.

6. Record your readings from each cylinder for future reference. Use the 15 psi criterion already mentioned to determine if further action is required.

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If compression readings are lower than normal for any cylinders, try a “wet” compression test, which will temporarily seal the piston rings, and determine if they are the cause of the low reading.

To perform this test, get a can of your favorite fogging oil and insert the red nozzle tube in the push button. Now carefully insert the other end of the tube into the spark plug hole and spray into the cylinder with a circular motion to distribute oil spray all around the perimeter of the piston. Spray for about four seconds.

Remove the nozzle and install your compression tester. Spin the engine over exactly the same number of times you did for the previous test and compare your gauge readings. If the compression rises noticeably, then your rings are beginning to stick.

If you’ve caught the problem early enough, decarbonizing with an “engine tuner” fluid, as described above, may cure it. If the dry compression was really low, and no change is evident during the wet test, it’s too late. Your rings and/or piston are worn to the point where major engine disassembly will be required. So be brave, and consult your dealer.

If two adjacent cylinders on a multicylinder engine give a similarly low reading, or if there was evidence of water or rust on the spark plugs from these cylinders, then the problem is a faulty head gasket. This is usually a problem better left for a professional to deal with, but if you have enough engine experience, you may want to tackle it yourself.

Incidentally, beware of compression readings from an engine that has been in storage for an extended period. While it’s sitting idle, the piston rings will “relax” and retract slightly, often giving an initially low and misleading reading. Always run an engine to operating temperature to ensure that the reading you get is accurate.

One last tip-if the spark plugs have been in the engine for the entire season, now’s the time to replace them.

Fuel System… The next phase of the annual inspection is to thoroughly check your boat’s entire fuel system for any signs of leaks, loose clamps, or cracked, frayed hoses and squeeze bulbs. Any rust patches on your fuel tanks should be sanded and touched up. Also, inspect the venting system for your fuel tank. It should be free to breathe. Any restriction can stop your engine.

An easy way to check for a fuel leak from the primer bulb to the engine is to squeeze the bulb until it gets firm, and hold pressure on it to be certain it remains firm while the engine’s not running. If it doesn’t stay firm, there’s a leak in the system between the bulb and the engine, or in the engine itself at the carburetor or fuel pump.

You may have to remove some access panels on your boat to do a visual check of the whole fuel delivery system, but don’t neglect this important task.

Automatic Oiler… Your next job is to check the automatic oil-blending system, if your engine is so equipped. Clean and inspect all lines and connections, replacing any cracked lines and tightening loose connections as required. It’s a good idea to check with your dealer for specific recommendations for your engine. On some engines, oil’ delivery pump diaphragms should be replaced as part of an annual service.

Steering… Your boat’s steering system needs to be thoroughly inspected at least once a year, but don’t hesitate to see what’s amiss any time you feel unusual looseness or tightness in the steering wheel. Inspect steering cables for any signs of separation, cracks in the outer sheathing, or rust buildup near the cable ends.

Battery… Next, check and clean all battery-cable connections and battery tops. Smear a light coating of Vaseline or similar light grease over the tightened connection. If you’re planning to put the boat in storage, remove the battery and trickle-charge it every month.

Two Final Adjustments. Last, you should have your dealer set your ignition timing, and adjust your carburetor(s). These are not procedures the part-time mechanic should attempt on an outboard engine. There are simply too many expensive tools required.

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