Our test boat had a pair of Crusader 350s for propulsion engines. These marinized engines are built up from GM 454 cid engine components. We toss around expressions such as marinized or freshwater cooled with abandon - what does it all mean?

The engine in your automobile is cooled with a thermostatically controlled flow of antifreeze/water mix. The heat is dissipated through the radiator before the coolant comes back into the block for another load of heat. A boat engine without freshwater cooling (all outboards, for example) depends instead on a thermostatically controlled flow of seawater to carry off engine heat. The seawater does a good job, but it's rough on the engine, particularly exhaust manifolds. These get clogged up with scale. A freshwater-cooled marine engine is set up like a car in that an antifreeze/water mix circulates through the engine. Since there is no airstream for a radiator, a different means of shedding heat is needed.

This need is satisfied by the heat exchanger. This is sort of a radiator in a closed, watertight tank. Hot engine coolant circulates in tubes which are bathed in a flow of seawater. Of course, this system requires two water pumps - one for the seawater and one for the antifreeze/water mix. Winterizing is more of a challenge too, with two systems to protect.

The payoff is engine life. A raw-water-cooled marine engine seldom lasts more than ten years. Aggravating scale problems and manifold replacement usually start sooner. A freshwater-cooled marine engine, though, is free to wear out from old age, instead of succumbing to salty hardening of the waterways. 

Of course, there's more to marinizing than freshwater cooling an engine. Your marine engine has many dissimilar components from its automotive kin. Electrical engine accessories, such as starters or alternators, are specially prepared. Because of the explosion hazard, they are shielded to keep any sparks outside. This is why you should never replace marine engine components with automotive parts.

This review/article originally appeared in Boating Magazine, April 1988 and is written by Allen D. Berrien. For more great powerboat reviews, visit their website and subscribe at: http://subscriptions.boatingmag.com/