Re: 3.0LX Mercruiser New Problem
... as it is somewhat rare to blow a head gasket on a marine motor.... Is this true?
Well first, did you see Don's question about the weather and if you had to winterize?
You should answer that question as that can provide some real insight.
Regarding if it is "rare" to blow a head gasket in a marine motor. Some of the guys that have worked with marine motors for many, many years might be able to give some kind of better answer with more specifics, or what "rare" might mean, here's how I (non-pro) look at it:
"Causes for Blowing
The main reason for head gasket failure is engine overheating, according to Mobiloil.com. When an engine overheats, the engine block and the head expand too much, thus damaging the gasket. But engine overheating is the not the only reason for gasket failure. Pre-ignition, or detonation, is the second leading cause, which can strain the valves, pistons and head gasket. This condition is caused by the engine being out of time. An overheated engine can also lead to pre-ignition and detonation problems."
In general, raw water is sucked in to either cool the engine directly or to cool (draw heat out of) a heat exchanger type system similar to what is used in an auto application. Water is also used pumped into the exhaust system to help cool that down along with running through power steering/oil/fuel coolers in many applications.
The raw water is generally drawn in via some type of impeller system where the impeller is of a rubber compound.
Should this impeller become damaged or worn out, the flow of water through the system can become reduced to where the engine will not receive sufficient cooling and heat/over-heat. Even a blockage on the intake port to the impeller can cause the same result.
Pre-ignition, detonation, bad timing can all take place with a marine engine and I'm sure maybe have even worst conditions with a marine environment.
The exhaust system is indeed something to check as if the exhaust manifold, risers, gaskets become compromised, water can enter the heads and engine to cause problems.
Mark
