Mercruiser engines, used in marine inboard and inboard/outboard motors, are very reliable. Still, as with all things mechanical, problems great and small can occur. Mechanics know an engine needs three things to run; those being fuel, air and spark.
Gasoline loses octane with storage so make sure the fuel in your boat is fresh. Marine fuel is often subject to water contamination. Be sure to have and maintain a water-separating filter on your boat's fuel system. Boats don't normally operate in dirty or dusty conditions, but there is a filter where the fuel line connects to the carburetor which can become clogged.
Since boats don't normally operate in dusty or dirty conditions as do cars and trucks, they don't have automotive style air filters. What they have is a spark arrestor which can become clogged with oil. Make sure the spark arrestor on the air intake on your Mercruiser engine is clean and dry.
Newer Mercuisers feature electronic ignition systems while older ones have contact points and a condenser inside the distributer cap. Both styles require regular maintenance as well as changing the spark plugs and spark plug wires on a routine basis.
Since boats often run in dirty or polluted water and the motors use raw water for cooling, Mercruiser and other brands of boat motors often suffer cooling system problems. Changing water pump impellors and engine thermostats on a routine basis is a good practice.
Just as automotive engines rely on multiple systems to operate perfectly, modern Mercruisers are equally complicated. Though rare, any of these systems can malfunction and cause operating problems.
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