Why Are Boat Engines So Unreliable? (9 Reasons Why)

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Bruce Coleman

Bruce Coleman is a diesel mechanic and car tester with 20 years of experience. He's a member of various vintage car clubs, and he loves restoring old motorbikes.

We all love spending a lazy afternoon out on the water in a boat. Smelling that fresh air and feeling the gentle bob of the water is calming somehow.

Yet, boats come with their fair share of problems, so much so that many people wonder if they’re worth the hassle. A common complaint is the one that usually revolves around the motor, leaving many boaters wondering, ‘Why are boat engines so unreliable?’

In this post, we’ll tackle this question and present you with possible reasons why this is almost always the case in many boats. Let’s dive in.

Why Are Boat Engines So Unreliable?

1. The Engine Has Overheated

Every engine has an exhaust system with pipes and mufflers to cool down the engine and muffle the noise. With all these parts, it’s easy to see how something can get trapped inside and cause the engine to overheat.

Not only that, but pieces of weed or a twig or any type of water pollution can get stuck in the pulleys or gears in the engine itself. If this is the case, you must remove whatever is trapped inside.

2. The Fuel Has Gone Bad

Keeping your gasoline-powered boat docked for long periods could lead to a moisture build-up in your engines.

Even if you don’t drive your boat out for just one season, it can cause condensation to accumulate in your engine, thus rendering it inoperable.

The best way to prevent this is to add a fuel stabilizer to the gasoline tank, especially if you’re planning on not taking it out of the harbor for a long time.

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Some boaters even add stabilizers each time they add fuel to the tank. It works by reducing condensation build-up and extending the life of your boat engine.

3. A Faulty Drive Belt

The drive belt, also sometimes referred to as a ‘serpentine belt,’ is typically a single piece of thick rubber. It drives the various peripheral devices in the boat engine, such as the water pump and alternator.

Since it’s constantly running, drive belts should be replaced yearly, or every 60,000 to 100,000 miles. Yet, if the belt is cracked or broken, you should replace it immediately.

To avoid being stuck out in the middle of the water with no help around, always carry a couple of spare drive belts in your toolbox.

4. You Typically Boat in Saltwater

Saltwater can take a heavy toll on the engine, and will add salt corrosion to your entire vessel.

One way to protect the boat is to give it a nice hose-down after each trip. Another idea is to scrape the salt build-up off the boat each season.

Finally, always flush the motor after each trip. It’ll help get rid of any impurities that accumulate within the boat engine.

Follow these tips to prevent any build-up that can potentially stall your boat engine.

5. Lack of Boat Engine Maintenance

Lack of Boat Engine Maintenance

Unfortunately, many boat engines fail because they aren’t properly cared for.

On the flip side, if you do your research and learn how to take care of your investment, it should last you many years.

This means you have to do your due diligence when it comes to figuring out what things can degrade the engine more rapidly. You also have to understand how all the parts work and what they need to stay in good shape.

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6. The Engine Propeller is Vibrating

The boat engine propeller is what transfers power, or thrust, from the engine to the water to get the boat moving. Propellers, or props, consist of two parts: the hub that supports the prop blades and the rotating blades.

If there’s a nick in any of the blades, it can cause an imbalance in the propulsion and cause the engine to vibrate. Also, a direct hit to the hub or a tangled fishing line can also cause vibration.

Your best option is to slow down and make your way back to shore. There, you can assess the damage.

7. You Run Out of Fuel

Unfortunately, boat fuel gauges are far from accurate. They sometimes read that the tank is a quarter full when it’s dry and sucking fumes.

Luckily, there are several ways around this problem. First, always fill your tank before leaving the harbor or marina. The second fix is to always store spare fuel with you on the boat.

Another thing we have to mention is you should get to know your boat’s range, like you do with your car. This way, you’ll have accurate calculations on how far you can go before the tank runs empty.

8. Failure in the Electrical System

A primary cause of engine failure is a faulty electrical system. It could be because of a bad battery or a malfunctioning alternator.

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If the electrical system is shot, the boat engine has no way of generating or distributing power to the rest of the parts.

In other words, the battery is either low and needs to be charged or dead and needs a replacement. Another problem could be there’s a break somewhere in the ignition circuitry.

Fixing electrical problems could be as easy as tightening up a bolt or replacing a few wires.

9. Spark Plugs Need to Be Replaced

If your boat feels like it’s losing strength, it could be the spark plugs are shot. Spark plugs take in the high voltage from one end and turn it into a spark at the other end, thus creating the combustion power that gets your boat running.

This is usually more common in older outboard motors. Nevertheless, you should always carry a handful of spare spark plugs on board.


Now that you have some basic boating knowledge, you can answer: why are boat engines so unreliable? It’s not that they’re more unreliable than other engines; it’s just that they have to deal with more variables compared with other types of engines.

Nevertheless, with regular maintenance and upkeep, your boat engine can be just as reliable, and you’ll be able to enjoy many years on your boat.


  • Bruce Coleman

    Bruce Coleman is a diesel mechanic and car tester with 20 years of experience. He's a member of various vintage car clubs, and he loves restoring old motorbikes.

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