One of the most common questions my marina customers ask me on a daily basis is what is the difference between marine and auto parts. Many people will ask for a part and when given a price will tell me that they can get the same part at the local auto parts store for half the price. It is something that people in the marine industry have been dealing with for many years. Most boaters are not aware of the differences in automotive parts as compared to marine and in some cases your life can depend on it. The parts with the most differences are the electrical and fuel systems, exhaust systems and cooling systems. Also, for many of the parts, it is illegal to use parts on your vessel that are not US Coast Guard approved.
In an enclosed engine compartment if there are any gas fumes there is the chance of fire. Electrical components for marine engines are meant to resist having exposed areas where there will be spark. Items such as fuel pumps, alternators and starters are all special for marine use. It is not uncommon a marine starter to be more than double its automotive counterpart. Marine spark plugs are built with stainless casings so they do not rust into the engine heads.
Cooling systems are another area where the automotive part is usually significantly less costly than its marine counterpart. In a sterndrive engine, the base engine is nearly identical to the automotive engine internally. However, the automotive engine is built with the intention of having a specialized coolant running through it helping prevent corrosion. Most sterndrive engines are cooled by water. If an automotive circulating water pump is used it will generally not last very long. In engines cooled with salt water they may only last a few months. Marine circulating pumps have special seals and are made with stainless and bronze internal components to prevent corrosion.
Marine fuel systems are far different than automotive systems. On a marine engine that is carbureted, the carburetor itself is built to prevent fuel from overflowing and spilling onto a hot engine. On a fuel injected engine in auto use the fuel pumps are generally located inside the fuel tank. In boats, for safety reasons, the fuel pump or pumps are located on the engine, secured on special brackets and connected with special fuel lines and wiring to prevent spills and stray sparks.
Engine internals are also specially built to handle what boats are made for, low end torque and camshafts meant to run at higher RPM’s for sustained time periods.
The proper parts may cost you more money when you purchase them, but for your safety and the safety of those boating with you remember that marine parts are the only way to go.