Chuck,

I realize your post is related to the boating time required to acquire over
10,000 engine hours but, in terms of engine longevity, you might be
interested in the following email response I received from Bob Smith at
American Diesel Corp. American Diesel sells replacement engines and
components and owns the inventory and intellectual property of the former
Leyman Ford.

I actually had the Ford Lehman in mind when I noted that some older trawlers
can be found with 6000-7000 hours. Big block per HP to create an ample heat
sink, slow rev, naturally aspirated, etc.

A friend of mine is a marine surveyor, and previously worked as an engineer for
one of the major diesel mfgrs. He is one of the few guys really qualified to do
mechanical and hull surveys at the same time. Jay has told me, (and he recently
wrote a magazine article reiterating the point), that
he is always doing surveys for people who
are buying a used boat with 3,000 - 4,000 hours on a marine diesel. He will say
that most of the buyers are very optimistic that they will get several thousand
more hours of service- even when he finds a few problems or the oil analysis is
very discouraging. The "diesels are immortal"
legend seems to fuel the optimistic fire.
My friend the Perkins dealer reports that
many well-cared-for engines simply wander off to the elephant graveyard before
they ever see 5,000 hours, and the only engines he is familar with that do
10,000 or more are in commercial fishboats, etc.

My previous engine went TU right around 4000 hours. I religiously change the
oil every 50 hours, and almost overmaintain an engine. In my case, it was a
physical failure of a peripheral part, rather than a loss of useable
compression, that caused a hydrolock and sudden failure. It's true that my
engine didn't "wear out", but it was broken beyond practical repair (unless the
Cheap and Dirty crew were hired for the job) in any case.

In about 40-years of servicing marine diesels, the Perkins dealer has arrived
at the conclusion that the most frequent cause of diesel failure in a pleasure
boat is a worn-out oil cooler. (My failure was due to a failed solder joint in
the turbo aftercooler)

The 120HP Lehman was originally conceived as a farm tractor engine, IIRC.
When run almost non-stop, they can last enormous amounts of time. I once saw a
maintenance manual for similar engines used to generate electricity at North
Slope oil field camps. There were a series of maintenance tasks to perform
"every 10,000 hours", and some major refits due
at the 50,000 and 100,000 hour marks.

I have lost track of the source, but there is a chart kicking around that
demonstrates the number of gallons of fuel that can typically be burned in a
diesel cylinder before excessive scoring and ring wear begins. A 6-cylinder
Lehman will burn about 1/3 gallon per cylinder, per hour, at cruising speed. In
6,000 hours, each cylinder will have burned about 2,000 gallons of fuel.
Compare that to some of the higher HP 6-cylinders that burn several gallons per
cylinder, per hour- and it helps to substantiate the observation that the high
revving, light weight, stressed-out "modern" diesels being asked to behave more
like gasoline engines than traditional marine diesels will also behave more
like gasoline engines when it comes to life expectancy.

I remain at odds with the statement that one can routinely nurse a pleasure
boat diesel to the 10,000 or 20,000 hour mark, (the number of years required to
do so notwithstanding). All the miraculous exceptions, and notoriously durable
engines like the small Lehman, simply prove the rule. The 10,000 hour pleasure
service diesel is probably about as rare as the 2700-hour gas engine: I
wouldn't say they don't exist, but neither would I count on typically getting
that sort of service.