posted 07-03-2002 11:59 PM ET (US)
The lifespan of an outboard engine is quite variable and depends on the way it was maintained and used.Of course, it depends on the original engine, too. Manufacturing tolerances were not quite the same in the 1970's as in the current decade. (In some cases they might have been far better!)
It is possible for an engine from the 1970's that has been well maintained and not run excessively hard or long to continue to provide good service.
It is also possible for an engine from the 1990's to be beat to death and on its last legs.
Things that keep engines running:
--fresh water operation
--short seasons
--out-of-water storage
--good maintenance
--careful off-season storage
--light load and lower RPM operation
--proper fuel and oil in proper ratio
Things that kill engines quickly:
--salt water
--year round operation
--in-water mooring or storage
--poor maintenance
--heavy loads and high RPM operation
--cheap gas and oil in improper ratio
To "rebuild" is generally understood to mean the powerhead section of the engine has been damaged and rebuilt. Often one of the cylinders will have a catastrophic failure, requiring the entire powerhead be disassembled, reconditioned, and reassembled.
It seems more common to rebuild higher horsepower engines because the replacement cost is many multiples of the rebuild cost. For example, a new 200-HP engine may be $12,000. To rebuild the engine may only be $3,000.
In contrast, rebuilding the powerhead of a 25-HP engine may not make sense. A new engine of that horsepower would be about $3,000 or so, and a rebuild might cost almost $2,000.
Total running time of an engine is a good indicator of remaining lifespan but it is hard to document. Most small boats do not have hour meters, and even if they do it is a simple matter to change out a meter (unlike a car's ODDOMETER which is proportionally much harder to modify or replace).
One number thrown out for average use is 50-100 hours per season for seasonal boaters. So a ten year old engine could have 500-1000 hours on it. Once past 1,000 hours you are probably living on the edge with many outboards.
That said, I know of some well maintained and lightly loaded outboard engines approaching 3,000 hours. That kind of longevity is exceptional, and it is not often achieved.
I bought a 1976 Mercury 50-HP and it has been running fine. It has needed some work. So far I have had to:
--reseal lower unit ($250)
--replace rectifier ($35)
--replace water pump impeller ($75)
--replace needle valves and floats; clean carburetors ($250)
--repair remote controls and lubricate ($50)
--replace primer bulb and fuel line connectors ($25)
So I have about $700 into the engine in five years of use, which is really nothing at all. Contrast that with a new engine of that horsepower and I am about $5,000 to the good.
I do confess that I really baby that engine, and since it is 26 years old I don't bet my life on it (if I can help it).
Can you tell by looking at an engine how it will run? Perhaps. I'd look more closely at the seller and gauge his honesty and integrity.