Marine Engines vs. Automobile Engines: Is there really a big difference?



One question that is often asked by consumers is “Why can’t I just put a car engine in my boat? You guys are using GM blocks, right?”

It is a valid question, one that is usually asked when a boat owner receives a repair bill or a quote on a new marine engine.

The answer is more complex than the simplistic “one has a radiator and the other has a heat exchanger” answer one may often hear.

Yes, MarineDiesel uses GM blocks for most of the engines we manufacture. However, the biggest reason that simply removing a diesel car engine of the same horsepower and mounting it in a boat will not work well is related to load. Most automotive engines are designed to produce some low-end torque and then simply use a small percentage of power to maintain a certain speed. Boats, unlike cars, are under continuous load: Resistance is always there in far greater amounts than a similar-sized land vehicle. Therefore, engines designed for automotive use typically do not produce sufficient torque to maintain or achieve sufficient speed.

Additionally, marinization requires strict adherence to standards against corrosion and wear, due to use in the marine environment. Therefore, an un-marinized diesel engine will corrode far more quickly, wear out quicker due to load, and not achieve the performance required in a marine application.

So why are marine engines so much more expensive?

Several reasons:

  1. The marine market is much smaller than the automotive or industrial market, so marine engines do not benefit from the economies of scale that automobile engines have. In other words, thousands of units are produced, rather than millions.
  2. Marinization is expensive. The marine environment requires higher grade components on virtually every system (fuel, electrical, etc.) than the non-marine environment. Seals and gaskets must be marine grade, as well as any metallic parts, from injectors to sensors, to wiring.
  3. Higher torque requires more robust attention to vibration and the resultant wear. Eg: Mounts must be much sturdier.
  4. Displacing heat is more difficult in the marine environment.

MarineDiesel knows the use and conditions that our engines must endure. They are designed for use in the proper environment.

Maintenance Tip of the Week – Wrench 03/31/2014


Maintenance Tip of the Week


Always use a torque wrench when tightening belts, clamps, and bolts on the engine. MarineDiesel are designed with specific components requiring specific tension.

Only from MarineDiesel: Battle Mode System (BMS)



MarineDiesel prides itself in developing engines that exactly meet our customers’ expectations and needs. Indeed, one of the main benefits of using MarineDiesel to power your fleet is that we can provide performance levels of which large manufacturers, such as Volvo Penta or Yanmar, can only dream.

One such product is the MarineDiesel Battle Mode System (BMS) that we offer optionally for our VGT Series of engines. BMS was developed specifically as a response to customer demand. Since a large portion of our production is military in nature, we offer this option to customers who need the specific type of performance required by military users.

Military vessels are often used for boarding moving ships. They require extremely rapid acceleration and crash stop capability, all without damaging the engine. MarineDiesel engines are all rated for heavy commercial or military use. They perform when some other engines, engineered for recreational use, will fail. MarineDiesel understands these needs and can engineer our engines to perform under the harshest conditions and use.

MarineDiesel VGT series – Battle Mode

The optional battle mode system BMS for VGT engines can either be manually activated or connected to a timer to get a timed actuation for boarding and other related operational requirements. BMS removes all safety functions in the ECU apart from audio and visual warning alarms. The standard safety systems implemented on all VGT engines are listed below, this include both de-rate and limp modes. The option requires a pin change in the ECU and must be pre-ordered; the wire is included in the extension harness to helm station.

                                                                                                    VGT450/VGT500             VGT300/350/400

Derate At:

* Coolant temperature                                                                     < 50 degC                                                 50 degC

> 85 degC                                                  80 degC

* Intake manifold temperature                                                      > 70/60 degC                                          85 degC

* Atmospheric pressure                                                                    < 85 kPa                                                      85 kPa

* Ambient Temperature                                                                   < 10 degC                                                   10 degC

                                                                                                      > 48 degC                                                  48 degC

Faults that cause limp mode:

* Electrical faults (sensor open circuit or shorted to ground/12V):

o RPM limitation and torque limitation

* Boost control fault (>70 kPa @10sec):

o Torque limitation

* Boost pressure high fault (>310 kPa):

o Torque limitation

* Coolant temperature high fault (>100 degC):

o Torque limitation

* Fuel rail pressure high fault (>200MPa):

o Torque limitation

* Oil pressure high fault (>500kPa):

o Torque limitation

Torque limitation set to: 60%

RPM limitation is set to: 2250rpm

To request BMS on your engines, simply request from your local dealer or distributor.

Maintenance Tip of the Week – Impeller 03/24/2014


Maintenance Tip of the Week


Inspect your impeller per the manufacturer’s recommendations, especially when a vessel will sit inoperative for long periods of time. Over time, impellers can stick to their housing if not moving. Damage, such as bent or chipped vanes, also hapers impeller performance.

Maintenance Tip of the Week – Strainers 03/17/2014


Maintenance Tip of the Week


Diesel engines produce tremendous amounts of heat energy, and that heat must be dispersed. Clogged strainers can ruin your engine quicker than just about any other cause. Always check your strainers for fouling and blockage.

Drives: Which to choose?



Many of MarineDiesel’s engines are sold as vessel performance packages, as a complete unit: Engine, Gearbox, and Drive, ready to install. Of course, you can always purchase an engine from us and install your own equipment, but packaging allows the shipyard to combine installation, commissioning, and after sale service into a package easily service by our trained technicians, often at a far lower cost than buying each component separately (Since we buy far more gearboxes and drives per year than the average shipyard and most of our partners pass warranty expense to us, we can sometimes deliver components at a lower price.)

This brings up the question: What type of propulsion should I use on my vessel?

There is no single answer other than, “It depends on how the vessel will be used.”

Each propulsion method has strengths and weaknesses.

For instance, on single engine installation, surface drives are not a good option due to torsional pull. On these vessels, a stern drive or water jet should be considered.

MarineDiesel has put together packages with all of the major drive types. What should you choose? See below.

Sterndrive: good trim and reverse. Good box size for davit operation. Traditionally not strong but Konrad and MD is. More drag than surface drive. Good steering. Easy to install and small inside build dimension. Cheap propellers. Normally integrated transmission (not Konrad). Trolling function with MD, joystick control, crash stop. Low cost.
Waterjet: Safety aspects, no propeller. Will not work if there is too much debris. Bad efficiency in low and mid range. Crash stop. Very durable. No trim capability. Must in most cases use transmission. Expensive. Good maneuverability.
Surface drive: Highest speed and most durable in most cases. Expensive propellers. Poor slow speed performance. Difficult to handle torque response in single engine installation. Must use transmission. Can be expensive.
Pod system: Easy to install. No trim function. Falls off on impact, expensive to replace. Designed for pleasure use. Good steering and available with joystick. Very expensive.
Shaft setup: Durable. Needs transmission. Medium efficiency. Complex for boat builder to install. Good reverse and medium steering. No trim.


Maintenance Tip of the Week – Belts 03/10/2014


Maintenance Tip of the Week


NEVER use automotive belts to replace worn belts on a boat. They are not designed to withstand the harsh marine environment and can easily fail.

Price matters, but here are five other, more important, considerations



When choosing between two engine types, there is much more to consider other than acquisition cost. MarineDiesel charges what we believe is a fair price for our engines… We are not the most expensive in our category, but we are also not the cheapest. If you are choosing an engine based purely on price, you will normally find cheaper products on the market. Indeed, as a company, we never make the cheapest price claim.

So what makes our engines worth a slightly higher price than some of our competitors?

Firstly, our marine line of engines are all V-8 engines, whereas nearly all competing products are normally inline 6-cylinder engines. The reason this is important is that V-8 engines produce far less torsional vibration than an inline four or six cylinder engine. Vibration impacts not only passenger comfort in a vessel, but also noise, and especially life cycle and Mean Time Between Failures (MTBF). The torsional forces produced by an inline engine greatly reduce the life cycle of that engine, and greatly increase the likelihood of catastrophic crankshaft failure. In a military or police vessel, this type of failure is highly problematic, and, for this reason alone, anything other than a V-configured engine should not even be considered. For more technical details of this issue, please download our brief white paper about Torsional Vibration.

Next, MarineDiesel engines are rated for heavy government, or commercial, use. Our competitors generally produce engines rated for recreational use. There is nothing wrong with that, but this means that such engines are generally not suited for operation under heavy use, exceeding 3,000 hours per year in some locations, and in the extreme climate conditions often found in such regions.

Derating. Though discussed previously on this site, most competing engine models are rated based on the climate where they are manufactured (normally in cooler, temperate zones). When operated in extreme conditions, these engines typically experience a power loss due to less efficient cooling from hot air and warm water. On some competitor engine models, this loss can be quite severe, sometimes approaching 50 bhp on a 500 bhp engine. For intermittent, recreational use, this may not present too much of a problem. With heavy commercial use, or mission-critical military use, the impact of this condition can be quite noticeable. Therefore, in order to obtain the engine performance and life cycle that government use requires, a customer may need to purchase higher horsepower engines to compensate for this power loss. Paying for a 50 bhp differential can easily erase any minor cost savings received. With MarineDiesel engines, all are rated for extreme conditions: In other words, under most conditions, when you pay for 500 hp, you receive 500 hp.

Programmable ECU. MarineDiesel is unique among engine maker in that we allow user programming of the engine’s ECU. Though several other manufacturers use this access to allow their dealers to make detailed diagnostic service in the field (as do we… The software is easily installed on a laptop and connected to the engine via a cable), none offer customization of the ECU. Why would we do this? The answer is simple. Many engines are used in vessels with unique missions and requirements. For example, most commando boats require very quick acceleration and rapid crash stop performance. By programming the ECU, we can “shift” the torque curve to a custom level, giving the vessel unique performance characteristics necessary to complete its’ mission.

MarineDiesel engines are built by hand, and extensively tested before they ever leave the factory. Engines are our ONLY business. Not construction equipment. Not trucks. Engines only. This level of quality control is impossible at larger manufacturers for whom engine sales may only represent a tiny fraction of their business.

Maintenance Tip of the Week – Oil Filters 03/03/2014


Maintenance Tip of the Week


Always use manufacturer’s recommended oil filters. Some aftermarket brands use inferior materials, like O-rings, that can easily fail, leading to very expensive repairs down the road.

Reference: MarineDiesel and Alamarin



The pictures below are on a recent project with the MarineDiesel VGT450 and Alamarin Jets. MarineDiesel has worked with Alamarin on many projects, and they are one of our partner vendors on engine packages. Alamarin are known for building reliable water jet systems that are easy to maintain and affordable.

You can read more about Alamarin on their website


on our site HERE

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