Common cause of marine engine problems
This is a copy of a recent post on my new blog, but is my own work and not anyone elses. I run a marine parts business and spend all day on the phone discussing marine engine related problems with folks and hopefully convincing them to buy parts from my company, the story below is a very common one
In my experience as an engineer and spare parts supplier, the number one cause of engine problems on older Gas (petrol) marine engines is Exhaust Manifold failure, (mainly on engines used in salt water), the minute an engine starts to misfire or run rough the owner goes through every concieveable option, (plugs, carb,leads, rotor, etc) but usually fail to notice the telltale signs of emulsified creamy deposit in the oil filler cap, and often the creamy oil in the sump, when they finally do accept that there is a more serious problem, they usually have a buddy who is “good with cars” and who instantly diagnoses the problem as a failed head gasket, and procedes to tear the engine apart, then (if you’re lucky and he follows the job through) he refits the heads and inlet manifold declaring the job ” good to go” the poor owner then arrives at the coast with the Wife, Kids (in wetsuits), Dog, skiis, Tube, and picnic baskets and proceeds to slip the boat, the engine often starts fine, runs for a minute or two then as the cooling system fills with water it starts to misfire just as he is reversing away from the dock, it then stalls, will not re-start and he hits another boat. :-(After a few minutes of cranking the engine and a bit of spluttering, he either gets a tow back to the slip, or paddles (with the skiis, wife on one side, him on the other, have you ever tried that) and puts the boat back on the trailer.
That would be a good scenario and ending, (apart from the thunder faced wife and kids, and the end of a beautiful friendship with the car fixer) it could also be a lot worse, (think coastguard rescue etc). if the car fixing friend knew anything about marine engines he would have gone straight for the exhaust manifolds rather than the head gaskets.
Marine exhaust manifolds are water cooled and most (Mercruiser, Volvo Penta, OMC, etc) Manifolds are cast iron, this material (although great for the job) is porous and spends its life soaking up the salt from the water that passes through it, until ultimately corrosion eventually breaks down the internal walls that separate the exhaust gas from the cooling water, the resulting hole then sprays salt water up into the exhaust ports causing all the associated problems,
for more information paste the following link into your browser http://www.watercraftservices.com/manifolds.htm
PS, If, as is often the case, the engine is left for a period of time before the correct diagnosis is made, (or even worse, pulled apart and left with the atmosphere getting to it) the corrosion damage (from contaminated oil) to the internal mechanical surfaces of the engine can be catastrophic.
BEWARE WHEN BUYING OLDER BOATS ON INTERNET AUCTION SITES, MANY OF MY CUSTOMERS HAVE BOUGHT BOATS ON THEM, AND THAT'S WHY THEY'RE MY CUSTOMERS !