Home » Auto Engine Marinization
Auto Engine Marinization

Auto Engine Marinization

When your boat needs a new engine and you have a spare one for an automobile lying around, it feels like you’ve got a match made in heaven.

The result isn’t quite that good unless you take some time to marinize the auto engine.

All automobile engines must go through a marinization process to ensure that the water doesn’t impact their performance. That means you must meet three thresholds when this option is what you decide to use.

  • It must meet all legal standards and guidelines as published by local, state, and national laws.
  • You need to have it meet the current safety regulations for boating.
  • It needs to last a long time by adapting to salt or fresh water, along with diesel or gasoline as the primary fuel.

Since a boat has a constant flow of new water, the engine experiences a higher risk and rate of corrosion.

Auto Engine Marinization

You can turn an auto engine into one for your boat when you take a few steps to marinize the different processes and parts. The primary steps to follow are to 1) change to a brass freeze plug; 2) change the distributor, starter, and alternator to their respective versions; and 3) use a USCG-flash suppression air filter.

You cannot ignore the two places with auto engine marinization: the head gasket and the freeze plugs.

If you’re rebuilding the engine anyway, you can snag the marine head gasket for your design to complete that step rather quickly. You can change the steel freeze plugs to brass ones after to reduce the corrosion risks.

Although you can theoretically use the steel plugs for your boat, you’ll need to replace them right away because of the water’s constant flow. That problem gets multiplied exponentially when your vessel operates in saltwater environments.

Once you take care of those tasks, the following steps to consider usually involve the legality and safety regulations that your engine must pass. These issues typically focus on the electrical and fuel system because of the fire risks you can encounter on boats.

No one wants their boat to explode because the wrong fuel or electrical components were used with an auto engine that wasn’t marinized.

◼️ What to Know About Fuel for Auto Engine Marinization

The marine carburetor is a little different than the ones used for automobiles. It’s designed to ensure the float bowls aren’t venting into the engine compartment, although the rest of the product appears visually similar to what you’d find on a car.

There is one significant difference that makes this upgrade a requirement. Should your fuel pump experience a ruptured diaphragm, it’s designed to contain everything when the failure occurs. Since that failure is the most common one that happens, boat owners don’t need the risk of having gas leak to places where it shouldn’t be.

When this issue happens with a car, it typically sends the fuel to the ground. Since you can’t do that with a boat, a secondary diaphragm is available. The gas gets contained by the second one if the primary unit fails, allowing it to flow out the drain.

Any gas that leaks will get dumped into the carburetor. If the leaks become bad enough, that means it’ll eventually flood the engine.

That outcome is much better than the alternative, which is a potential explosion.

◼️ What to Know About Electrical Upgrades for Marinization

When you have a starter and alternator firing, the rotating shafts with electrical contacts create sparks. If you have fumes, they’ll ignite. That means the entire boat is at risk unless you take the time to marinize the auto engine.

The best way to prevent sparks from firing is to use a marine alternator and starter combination. This technology uses flame suppression without compromising the ability to get the engine to turn over. They’re not sealed, which means an arrester works to prevent movement toward the outside once turned.

It’s possible after marinization for some gas fumes to enter the alternator or starter and ignite, but the case is designed for this circumstance. It holds the explosion in the container while arresting the flames from reaching the rest of the boat.

The distributor follows the same idea when working toward auto engine marinization. It arrests the flames to create a safer starting and user experience.

That means the electrical system gets designed to avoid igniting fumes. When you have the fuel system modified for the boat, it is intended to prevent the accumulation of combustible flames.

It is a combination that does an excellent job of ensuring that you receive the safest experience possible when converting an auto engine into one that works for your boat.

You should buy the marine versions of the alternator and starter to get the best results. Although the price is significant, it is essential to remember that gasoline fumes tend to skin to the bottom. That’s where the starter sits, which means the fumes go there when the vessel remains idle.

Since the starter is the first electrical item used on most boats, you must avoid spark creation.

Why Auto Engine Marinization Isn’t Always the Best Idea

When you need a new engine for your boat, it might be better to invest in one made for your make and model. Although some auto engines can drop right into that compartment, the fact remains that the unit was built for a car – not a vessel.

If you decide to work on marinizing your auto engine, you’ll need to create a plan to counter these potential problems before hitting the water for the first time.

Engine Duty:Auto engines are meant to be a limited-duty unit. That means you turn them on or off regularly so that they’re not constantly running. Marine designs are meant for continuous duty, which means they can overheat when the throttle is left wide open or idling.
Part Differences:Although marinization on the key points to preventing flames and sparks is essential, several differences exist for the cooling and oiling system, valve timing, and the exhaust. When those items break on a boat, whatever warranty was associated with the product is likely voided.
HP Derating:When an auto engine gets marinized, its peak horsepower rating decreases. Even when boaters cruise without a wide-open throttle, you’ll be using more of the rated power for the engine. Cars use about one-quarter of the HP rating to maintain a steady speed. Boats can use up to 75% in return.

◼️ What About the Transmission?

A consideration for most marine engines is the need for a transmission. If you use a marinization conversion kit, this essential requirement often gets included as part of the conversion kits.

The standard auto transmission isn’t practical to use on most boats. That’s why it gets disposed of during the conversion process, along with the clutch.

Even automatic transmissions found in cars today get included in this category, although there is the occasional exception to consider.

Since boats don’t have brakes, the arrangement must be that the reverse throttle can engage to stop or slow the vessel. That’s why a marine transmission is almost always coupled to this result.

If you don’t couple the transmission to the engine, you’re running what is called the bobtail setup. This design works for jet drives and sterndrive units, but it is also possible for some V-drive installations to use it if the transmission function is part of that unit.

The engine gets started in gear, with the boat taking off as soon as everything starts working. If you use this design for your vessel, the only way to stop it is to turn off the engine. That makes it dangerous to use, which is why it is not typically legal unless you’re operating a racing boat under specific conditions.

Areas to Review During Auto Engine Marinization

Since an auto engine contains various parts of different shapes, sizes, and purposes, the actual conversion process is quite unique. That’s why it helps to pay attention to some specific areas to ensure that you complete the process correctly.

Here are some of the areas to review before firing everything up for a day on the water.

1. Water-Cooled Exhaust Manifolds

In boats where the engine gets enclosed in a confined space, its heat can be hazardous. It can cause it to hamper airflow and movement, producing overheating problems that can lead to its seizing.

That’s why many exhaust manifolds get cooled with water-jacketed manifolds. Only competition boats are typically permitted to use air-cooled technologies.

2. Water Pump

Cars, trucks, SUVs, and vans use a recirculating-type water pump. It’s not intended to actually pump the fluid, but to keep everything moving. When you have a marinization process to complete, the marine pump must push water into the cooling system to operate correctly.

That means the entire system must be built to withstand the potential issues of saltwater and corrosion. That’s why most marine pumps are made with a rubber impeller type that resists silt, sand, and salt.

3. Tilt Shim

Most marine installations have the engine set at an angle from the horizontal plane. That’s quite different from most automotive designs that keep everything relatively level.

Gasoline engine carburetors are designed to work with the latter, which means you must bring it back to the correct plane for operating in a vessel. That’s why a tilt shim is necessary, with several different angles to consider based on your needs.

You can also find several throats or barrels available when shopping for tilt shims to finish your auto engine marinization.

4. Engine Mounts

Since the engine usually fits to motor stringers or something similar, a special mount is often necessary to complete the auto engine marinization process. They are sometimes separate components or included as a built-in addition. You can use rubber or rigid options, with the four-point-mount considered the industry standard today.

5. Oil Filter Relocation

When you run a converted engine in your boat, the location for the oil filter could make it inaccessible on the vessel. Kits are available to relocate it to a more convenient place to ensure you can service the engine correctly.

It’s common to add a water-cooled oil cooler in line with the filter since the temperatures are often higher than what gets produced with an automobile.

6. Cover Plates

Several cover plates could be necessary to complete the marinization process. Flywheel covers, water-cooled manifolds, and starters often need this asset to provide a safe user experience. Timing gear covers are sometimes required if a cam-driven water pump is part of the design. Any belts of pulleys often get this treatment.

Is It Worth the Cost of Completing an Auto Engine Marinization?

The price of a boat engine rebuild can easily exceed $4,000 before labor costs get calculated. If you only need to replace the seals and bearings, the price for a rebuild could be as low as $800. It makes sense to complete the auto engine marinization process if that expense is cheaper than a more traditional option.

I’ve found the biggest problem with an auto engine marinization project is the cooling network. Since it isn’t designed to cool evenly when placed under a heavy load, allowing the front cylinders to get more than the rear. The center cylinders have less surface area for cooling, which means they run hitter than the engines.

That’s why a continuous-duty engine can operate consistently when one designed for automobiles tends to overheat.

Although you could operate the engine at half-throttle to have it usable, the cost savings don’t always equate to the results you get. It’s usually better to invest in a proper marine engine.

Unless you get the cooling right, you risk a cracked head, cracked manifold, or worse if cold water gets put into the hot engine.

Should you pursue auto engine marinization, please remember to use Coast Guard-approved or mandated parts in your vessel to ensure it is compliant with all local regs.


Attention: You have to take care of your own safety and health. The information on www.vehicletrooper.com only serves for learning and entertainment purposes and is not intended to serve as a substitute for the consultation, diagnosis, and/or medical treatment of a qualified physician or healthcare provider. Before you use any equipment or vehicle, make sure you have been properly instructed by an expert and adhere to all safety precautions. This site is owned and operated by Media Pantheon, Inc., Media Pantheon, Inc. is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for websites to earn advertising fees by advertising and linking to Amazon.com