Marine automobile engines are types of automobile petrol- or diesel engines that have been specifically modified for use in the marine environment. The differences include changes made for the operating in a marine environment, safety, performance, and for regulatory requirements. The act of modifying is called 'marinisation'. All of the "Big 3" American auto companies have had engines marinised at some point. Chrysler is notable, because the company marinised engines in-house through Chrysler Marine, as well as selling engines to third parties such as Indmar or Pleasurecraft Marine. General Motors marine automobile engines are based on a gasoline truck engine. That means four-bolt main bearing caps instead of just two; sometimes the crankshaft is forged steel and the pistons an upgraded aluminum alloy. Most importantly the camshaft profile is different with the overlap ground to 112 degrees instead of 110. Expansion plugs are bronze to better fight corrosion. The head gasket's metal O-ring is also more corrosion resistant. Examples of the opposite of a marinized car engine also exist, e.g. the 6,2 or 6,5 liter Detroit Diesel V8 engine found in Chevrolet and GMC utility vehicles was originally a marine engine adapted for automotive use.
Safety modifications
;Electrical systems
Marine starter motor – it has an internal screen to minimize the egression of spark movements.
Marine alternator differs from an automobile alternator – it has an internal screen to minimize the egression of spark movements.
;Fuel systems
Fuel pump vented – if the fuel pump diaphragm ruptures, then the excess fuel will be directed into the carburettor. This kind of fuel pump is referred to as a marine fuel pump.
Marine carburettor does not allow the overflow into the boat engine compartment.
Spark arrestor on the air intake – a wire mesh screen on the spark arrestor cools any internal flame or spark created by back-fire, thereby preventing it from igniting fuel vapours inside the engine compartment.
;Fuel systems ;Cooling systems
Marine automobile engines are water-cooled; drawing raw water in from a pickup underneath the boat. In an open cooling configuration, the raw water is circulated directly through the engine and exits after passing through jackets around the exhaust manifolds. In a closed cooling configuration anti-freeze circulates through the engine and raw water is pumped into a heat exchanger. In both cases hot water is released into the exhaust system and blown out with the engine exhaust gasses.
The marine distributor does not have a vacuum advance. Vacuum advance is normally actuated at high engine revolutions per minute in low load situations - and this situation generally does not occur in the marine environment. Under normal operation, high rpm generally means high engine load.
Lubricating oil system. 1.Lubricationg oil is cooled in a shell and tube type heat exchanger by sea water or river water as the case may be. 2.The lubricating oil sump at the bottom is bigger and often has a different shape to take care of rolling and pitching.
