Issue: November 2008
NAUTICAL KNOW-HOW: Outboard Troubleshooting 101



Oh, pity the noble backyard mechanic. Pity the poor do-it-yourselfer who can no longer fix his own sputtering outboard. The internal combustion engine used to be a pretty simple machine, but now you need a laptop and a four-year engineering degree just to get the hood open . . . right? Well, no, not really. Outboard engines are far more complicated than they used to be, and sometimes we are at the mercy of the high-tech witch doctors. But still, even nowadays, most of the things that can go wrong with your outboard can be simply diagnosed and fixed--by you, on your own boat, with simple tools. All you need is some basic troubleshooting knowledge and an opposable thumb.   

Follow That Ampere
Electrical problems are very high on the list of common reasons to call a towboat. They're usually exemplified by the failure of the motor to turn, failure to start, surges, and misses. And nine times out of ten the issue can be easily traced and fixed. First you want to be sure you have a fully charged battery onboard. If you don't, there's not much you can do but call for help. How will you know if the battery is your problem? Try tilting the outboard up and down one time. If it moves at the usual rate of speed, you know you have plenty of juice. If that's the case and you still get nothing when you turn the key, the next order of business is to make sure you've got the throttle in neutral. Yes, yes . . . you're an experienced boater and you already checked that--but do it again. Even if it looks right, shift in and out of gear once or twice, listen for the clicks, and be absolutely sure it's in neutral. You'd be amazed how often boaters are "rescued" with this simple fix.

If all's well with the throttle, our next suspect should be the connections at the battery and at the starter. If you see any green and white crud, you've probably found the problem already. Remove the wires, make sure the connections are perfectly clean, and retighten them.

So now, let's say the starter cranks, but the engine won't catch and run. This is another common problem, with another common culprit: the kill switch. Even if the lanyard clip is in place, the switch may prevent starting. This is not unusual, especially with switches mounted horizontally on top of the helm station. In those cases, water will often pool around the switch and eventually get inside it, causing a short. Luckily, on most engines it's fairly easy to disable the switch; simply look for a black wire with a yellow stripe that leads to the switch. Disconnect it and try the key again.

Fuel and Flow
Fuel issues are, of course, another reason why outboards may fail to start, miss, or run intermittently. These problems can be harder to solve on the spot, particularly if they relate to a complete absence of fuel. Hey, don't laugh, even the best of us has run the tanks dry at one time or another. Remember that marine fuel gauges are notoriously unreliable, so always double-check your fuel supply before leaving the dock.

If you can't get the motor running and you know there's fuel onboard, make sure it's getting to the motor. The easiest way to do so is to look at the primer ball. If it's sucked in tight, you may have a blocked fuel vent, which isn't allowing air to displace the fuel leaving the tank. (This is a common occurrence when running a small motor on a portable fuel cell, which has a thumb-screw type of vent. Boaters often close the vent after a day on the water, then forget to re-open it on the next trip.) If the primer ball looks okay but is easy to squeeze and doesn't get harder as you pump it, then you probably have a leaky fuel line--which is either sucking in air or spurting out fuel. Or you may have a bad connection at the tank. Finally, check the filters and/or fuel/water separators. If these are clogged, obviously, that can also prevent fuel from getting to the motor.

If the fuel system appears to be operating properly but you think you have water in the fuel (expect sudden shut-downs or bogging, and periods of misses) on boats with multiple fuel tanks (but not enough fuel in any one tank to get home on) you may be able to get home using this trick: Partially open the valve between the tanks, so the motor(s) draws from one more than the other. You may find that one tank is problematic and the other is not, and you may also discover that you can try different "mixes" to get it running, then head for home and some water-absorbing fuel additive.

Keep Your Cool
The cooling system is another common cause for a misbehaving outboard. Always keep your eye on the telltale--which, after all, is there to tell you whether or not the flow of cooling water is up to snuff. If the telltale isn't peeing freely but the engine seems to be running normally, it's likely that the telltale port is clogged--a problem that can (and should) be solved by threading heavy (60- to 80-pound test) monofilament fishing line through the telltale and spinning it around. This is enough to break most minor clogs free.

If, on the other hand, the telltale stops peeing and your temperature alarm goes off, you've got a bona fide problem--though you'll be happy to know that the most common cause of this is also the easiest to fix: blocked intakes. After shutting the engine down, tilt the motor up and check the intakes for clogs. If they're clear, the next most likely issue is a bad impeller, and that's a bigger problem, especially at sea. Even if you carry a spare impeller, chances are much greater that it will end up on the bottom of the Bay rather than properly installed in the lower unit.

What if your temperature gauge is going berserk, yet you're positive the cooling system is functioning just fine? If you have a direct-injection two-stroke, the problem may be in the oil pump--which in most modern outboards will be indicated with a warning light. If all seems well with the oil pump, the next suspect in line is the thermostat, which may be stuck. Sometimes you can pop it free, scrub off the grit or grime that has it clogged, and get under way again. If the thermostat is shot, you might indeed need a tow. If you have intermittent overheating problems and you suspect a bad thermostat, there's a very straightforward way to find out if it's working or not. Simply remove the thermostat and, using a pair of tongs, hold it in a pot of water placed on the stove. Put a thermometer in the pot as well and watch the temperature rise as you turn up the heat. If the thermostat doesn't open at the correct temperature (refer to your owner's manual to find out what it is for your specific outboard) then you know it needs to be replaced. If it does open, something else is amiss.

Bad Vibes and Mysterious Sounds
Extraordinary engine vibration is another cause for concern, and your prop usually holds the answer. Bent blades, large dings and chinks, and any damage to the blades can cause the engine and boat to shake hard enough to rattle your fillings out. If you carry a file onboard you can try some emergency repairs--just file down the offending sections of the propeller--but usually you'll simply have to live with the problem until returning to shore. One caveat: Make sure you reduce speed, and go home at a crawl if necessary, to eliminate all that shaking. If you run the boat hard with excessive vibrations, there's a good chance you'll do serious damage to other parts of the boat.

Motor mounts are also surprisingly common culprits when this issue crops up. You wouldn't think to check them often, but when excessive vibrations start shaking your boat apart, look at the motor mounting bolts and the mount itself. Make sure the nuts and washers are flush with fiberglass, and if anything has backed off, take a wrench to it. Mysterious sounds can also be alarming at times, and you can use several troubleshooting tricks to identify problems that are tough to diagnose. When you hear a funny noise coming from the engine but you can't isolate it, for example, use a screwdriver as a stethoscope. Simply put the tip of the driver up against the different parts of the engine and put your ear next to the handle. The screwdriver will magnify the sounds, helping you to figure out exactly where they come from.

Of course, this is a pretty basic guide to outboard troubleshooting, and we've only touched on the issues you can address while on the water. But when you're having trouble away from the dock, you'll find that eight or nine times out of 10, it's one of the problems covered here. And now, you'll know how to fix it.