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.