What Is the Difference Between Marine Motors and Car Motors?

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.

What’s the difference between Marine & Automotive Engines?

Marine Motors Can Resist Corrosion

One of the most important differences to know is that marine motors are meant to withstand a constantly wet environment. This means all the parts on them can resist the corrosion that comes from being underwater. So the head gaskets, freeze plugs, valve guides, and other motor 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 keep up. This is why the camshaft of a marine motor is built to use as much low-end torque as possible, rather than high RPM horsepower like a car engine. Essentially, a marine engine has just one gear compared to the four or more that a car engine has. This is another major difference between marine motors and car motors.

A Marine Motor’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 ones 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 engine 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.

Car engines are often cheaper than boat engines.

Boat Motors 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 motors are not built to be used the same way as car engines. This is why you can’t simply use a car engine in place of a boat engine.

Marine Motors Come in a Few Varieties

So now you can see that there’s enough of a difference between marine motors and car motors that they’re not interchangeable. That means you should prepare to buy a marine motor for your boat. But which one should you buy? This requires you to learn the differences between the most common types of marine motors.

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 wall 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 motor usually features 2 or 3 cylinders, though you can find it in V-6 and V-8 varieties, as well. Typically, this motor uses the power of jet propulsion to move the boat.

Another popular option is the inboard motor, which uses gas or diesel fuel to get the power it needs. With inboard motors, the rudder, shaft, and propeller go underneath or inside the boat. With this type of marine engine, you’ll typically get 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 outboard motors.

Of course, the marine motor 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. Regardless of the marine motor you choose, you can come to Gold Eagle for all the marine products you need for your boat!

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15 Comments
  • You got to learn something everyday. I’ve seen a marine motor ones and it doesn’t look complicated until you know these components are engineered with extra safety and protection against salt water.

    • if salt water is not a concern, will a regular 350 block work with a boat if alternator, starter, and carb are off a marine motor?

      • Simply NO Marine engine is a different animal.

      • Adam that is not exactly true. i’m an early teen and I swapped our runabout with a big block 405 and it runs amazing. But Doug, you will have to replace the camshaft, sparks plugs with marine ines built for a 405 and you need to make the oil reservoir bigger and make a cut out for your radiator

  • Thank you for information.

  • One of the most important differences to know is that marine motors are meant to withstand a constantly wet environment. This is the perfect blog for anyone who wants to know about this topic.

  • Do marine engine have problem with conventional lubricant like heat transfer and wear problem?

  • I want to install a marine 350 engine in my truck, is it possible?

  • My dads old boat had marinated bmw inline six car engine inboard, and i have seen my fair share oh marinated toyota truck engines in inboards around where i live

  • I was an engineer for FORD motor company for 27 years, we disassembled more 302 engines and rebuilt them for multi purposes than I can count; To use a car engine in a boat requires only a few substitutions of parts , all external. when we build the V8 motor at our plant, some go marine some go auto- there is NO internal difference in the Blocks and heads , including the freeze plugs in fresh water. 1500 hours is a relative number, regular flushing of the block, use of the highest quality synthetic oil, warming up the engine properly and storing the boat if possible in a garage will give you extended engine life- cheers!

    • Maybe on a ford production. I don’t know. On GM…. Not the same internal parts ! The cam and heads are specially produced for marine engines ! The block is the same, with the exception of brass freeze plugs. If you run constinate lake water over steel vrs. brass which one do you think will rust? refer to Adam in Aug.

    • Maybe on Ford production, I do not know. On GM there is a difference between auto and marine engines. The cam and heads are engineered for high rpm HP, not bottom end. The heads have different valve seals. The block is the same, with the exception of brass freeze plugs and all fiber head gaskets. If you run lake water over steel vrs. brass, which one do you think will rust out first?

    • I love this kind of discussion! The external parts I mentioned above include freeze plugs where applicable, in Texas where I am retired now, not an issue- would I give my grandson some tips to extend the life of a motor used for marine applications? Sure!! , wise idea using a higher volume than stock oil pump, using the absolute best synthetic oil available , putting an RPM governor limiting engine RPM’s, regular or constant use of the engine is important , the engine heat will dissipate moisture in the engine compartment- but….weeks/ months / years of no use is always a bad thing for engines ( same with airplanes) . Now is fuel injection better than carburation? is a larger oil sump better than stock? is a pressurized ( after market) oil system awesome? does removing the boat from the water and putting it in a temp controlled garage help? sure….we can outspend ourselves on modifications but what for? going fishing? …all this old man is saying is that a crate Ford motor will work in a boat or a car with a few mods- I was at ford field for a Tiger game years ago….this young guy comes in with his dad bragging about the mods he made to a F150 4×4 truck and motor….he looks at us and says why are you laughing? my boss at the time says we spent 20 million cumulative to engineer that truck and drive train and you guys with 1500 in after market parts mess it up…my boss says …4×4 is too get you OUT of trouble not into trouble…i laughed and said- were getting old….

  • Could you put a Volvo b30 in a car

  • I have purchased what the salvage yard says Is a marine block but it has the words Camaro wrote on it. It has a stamp that reads, 397 (? Not sure what this Mark is) 010. It also has Mexico stamped on it.
    Anyone know if this is a marine block?