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SOME DIFFERENCES BETWEEN AUTOMOTIVE & MARINE ENGINES

For those of us in the marine industry, a common occurrence is to be questioned by customers about auto vs. marine parts.  A common scenario is to have a customer ask for a replacement part for his boat.  The part in question is a starter for a 350 cu.in. GM block.  You give the customer a price, and he looks at you with a blank look on his face.  He, then states (very angrily) "I can get one at the local auto retailer for $29.95".

In the marine industry, this little scenario occurs all the time.  Many boaters are unaware of the difference between an automotive and a marine engine and their respective accessories.  The most notable differences include the exhaust systems, the cooling systems, the electrical systems, and the fuel systems. Additionally, items such as heads and cams are usually different.   For the purpose of this article, we will only be hitting the highlights on select systems.

In regard to the cooling systems, one of the major differences is found in the water-circulating pump.  This is especially noticable when you have a raw water cooled engine.  Unlike their automotive counterpart, a marine pump works in an open cooling system.  This type of system is extremely corrosive to the pump.  Therefore, the pump must be altered for longevity.  A marine pump has a special ceramic seal, stainless steel backing plate, and a bronze impeller to resist corrosion.  An automotive style pump, with its stamped steel impeller, would fail due to corrosion in a short time.

The electrical systems in a marine application are also extremely specialized.  In an automobile, any gasoline vapors that accumulate will readily dissipate through the bottom of the engine compartment.  However, a boat with its sealed engine compartment, does not have that luxury.  Therefore, any spark could literally cause a boat to explode.  All electrical components in a boat are either completely sealed or specially vented to prevent such a catastrophe.  This includes the starter, alternator, distributor, and many other engine electrical components.

Carburetors typically have what is known in the industry as J type fuel bowls.  These allow for the extreme vibration, pitching and yawl experienced on boats.  This allows fuel to be drawn in exteme conditions and keeps fuel from being ejected from the carburetor barrels.

Heads and cams are set up for a completly different torque curve.  A marine engine must develop most of its torque on the low end of throttle range.  This allows for the ability to use a single gear transmition system.  Think of it this way:
You get in your car
Start it up
Drive to the highway
Put your foot to the floor and hold it there for an hour
Its a little different, well for most of us.

Although we have only briefly touched on some of the differences between an automotive and marine application; hopefully, it will serve to remind us that there is a difference, and that the reasons for these differences need to be shared with our customers and friends in the boating community.  Hopefully, when shared, this information can eliminate some of the "blank stares" in regards to parts, and maybe prevent some dangerious situations. 


Copyright 2003, 2004, 2005, 2006, 2007 Boatfix, Inc.  All rights reserved.

Boatfix.com specializes in marine engine parts and boating accessories; including risers, manifolds, alternators, starters, water pumps, bilge pumps, pistons, gaskets, lifejackets ( PFD ), hoses for Mercruiser, Crusader, OMC, Volvo, Sea Maxx, Evinrude, etc. (Gas and Diesel)- you name it.  If it goes on a boat, it's in our catalog!