What Is the Difference Between Marine Engines and Car Engines?

What Is the Difference Between Marine Engines and Car Engines?

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There's More Than Meets The Eye


If you’re fixing up your boat, you might be thinking about replacing your old marine motor with a new one. As you look at the engines on the market, you might notice that automobile motors are often cheaper than marine motors. So are they interchangeable? And if not, what is the difference between marine motors and automobile motors? Here’s what you should know before you get a new motor for your boat.

Marine Engines Can Resist Corrosion

One of the most important differences to know is that marine engines are meant to withstand a constantly wet environment. This means all the parts on them can resist the corrosion that comes from being in a salt water environment. So the head gaskets, freeze plugs, valve guides, and other engine parts have to be made of corrosion resistant materials.
That’s not a common requirement on car engines, though, which are meant for dry environments. This means the two types of engines are not exactly interchangeable.

Marine Engines Are Heavy Duty

A car engine typically only uses a portion of its horsepower to maintain a decent speed on the road. On the other hand, a marine engine is essentially at full throttle all the time just to move it through the water, so it has to be pretty heavy duty to maintain this pace.
This is also why the camshaft of a marine engine is built to use as much low-end torque as possible, rather than high-end RPM derived horsepower like a car engine is. Essentially, a marine engine has just one available gear compared to the four or more gear ratios that a car engine has available. This is another major difference between marine engines and car engines.

A Marine Engine’s Major Components Differ from a Car Engine’s

You should also keep in mind that the alternator, distributor, and starter in a marine engine are all different from the same items used in a car engine. In a marine engine, these all have special screens that can extinguish internal sparks so they don’t light the gas fumes in the boat’s bilge area after venting into the atmosphere. If you try using a motor that doesn’t have these screens, you risk damaging your boat and creating a dangerous situation for anyone nearby.

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Boat Engines Are Used Less Often

Typically, a car gets used every day, or at least several times per week. This is good for the engine, battery, and other components, since they often lose power or generally become weaker when they sit unused for too long. But many people don’t take their boat out nearly as often as they drive their car, so it makes sense that marine engiines are not built to be used the same way as car engines. This is another reason why you can’t simply use a car engine in place of a boat engine.

Marine Engines Come in a Few Varieties

So now you can see that there’s enough of a difference between marine engines and car engines that they’re not interchangeable. That means you should prepare to purchase a marine specific engine for your boat as opposed to a car engine. But which one should you buy? This requires you to learn the differences between the most common types of marine engines.
First, there’s the outboard motor, which is especially popular on fishing boats and pleasure boats. The outboard motor is self-contained, with the propeller, engine, and steering control all in one unit that attaches to the back transom of the boat. This is convenient because you can lift the whole unit out of the water when you winterize your boat. This type of marine engine usually features 2 or 3 cylinders, though you can find it in V-6 and V-8 varieties as well.
Another popular option is the inboard engine, either gas or diesel powered. With inboard engines, the rudder, shaft, and propeller go underneath or inside the boat through the transom to an outdrive. This is known as an I/O (inboard/outboard) application. With this type of marine engine, you’ll typically employ 4 or 6 cylinders, much like you would with a car engine. That’s why this type of engine is typically considered more powerful than an outboard motor.
Of course, the marine engine you choose should be the one that best fits your boat and all its components. So just as with your car, you should read your owner’s manual before choosing the best engine for it.

Article courtesy of GoldEagle.com. The contents of this article are for informational purposes only and are not intended for diagnosing. Boating Basics does not guarantee - expressed or implied - any specific results and a professional should be consulted on more serious issues.

We hope this article has helped to explain many of the various differences between marine engines and car engines as well as the importance of knowing those differences. At the end of the day it comes down to the best engine for the job at hand. And that means using a marine specific engine to power your boat.