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I wish I could recall where to find it, but there has been a study
conducted and a theory advanced that there's a direct relationship
between the amount of fuel a diesel engine consumes and its life
expectancy. The theory bases life expectancy on gallons consumed,
rather than on hours operated. Under such a premise, any fuel
consumption chart for a high HP diesel engine will reveal just how
costly pushing the engine beyond
the most efficient point in the curve can be, in terms of engine life
expectancy as well as the fuel bill. I wonder what your acquaintance's
experience would have been at just a few hundred RPM slower, where his
fuel consumption might have been substantially less. If he's wearing
out a diesel in 1000 hours, he's got the wrong engines for his
application or he's pushing them way too hard, IMO.

Relevant aside: I was just aboard a new Silverton with Yanmars, and
learned that the factory *recommends* that the engines be cruised at
within 200 RPM of WOT and *recommends* that they run totally wide open
for up to 30% of total operating time.
Interesting recommendations, to say the least.


The manual for my Volvos (TAMP-63P -370hp) says the same thing, in fact they
give you a placard to install by the throttles that says "Recommended cruise
RPM = WOT minus 200 RPM. Doesn't say anything about running WOT
specifically, but general knowledge among diesel owners is to crank 'em up
for a mile or two when returning after cruising for an extended period of
time.

The theory on engine life and fuel consumption makes a lot of sense. As I
mentioned, the person with the 600 hp Yanmars does a lot of fishing and it
includes many hours of high speed, (30+ knots) running to get well offshore
(NE Canyons). His boat was manufactured by:

http://www.eastbayboatworks.com/

RCE

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RCE wrote:
wrote in message
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I think (simply my opinion) that a modern diesel boat engine's lifespan
is
inversely proportional to it's horsepower. I know a guy that's been
through
3 engine rebuilds or replacements of both Yanmar 600 hp engines on his
boat
in 6 years. He did a lot of fishing trips and never got much over 1000
hours
on any of them.

RCE


I screwed up. His engines are *not* Yanmar. They are Manns.

RCE

On 20 Feb 2006 07:21:46 -0800, wrote:

I wish I could recall where to find it, but there has been a study
conducted and a theory advanced that there's a direct relationship
between the amount of fuel a diesel engine consumes and its life
expectancy. The theory bases life expectancy on gallons consumed,
rather than on hours operated.

Fuel consumed relates directly to horsepower generated times hours of
operation, and is more or less meaningless as a durability indicator
except between comparable engines. What are very definite indicators
however are horsepower per pound and horsepower per cubic inch. The
Yanmars rate poorly on both counts since they are light weight, highly
stressed, turbo charged engines putting out a lot of power for their
weight, actually weighing less than the 350 hp gas engines that they
replaced. All turbo charged diesels are high maintenance relative to
their naturally aspirated brethren but some are more conservatively
engineered than others.