T&T: Engine longevity

David&Joan djmarchand at cox.net
Fri Apr 20 21:56:22 EDT 2007

The experts over at boatdiesel.com have this to say about engine wear and 
slow speed running:

Operating a modern, turbocharged diesel at 30 hp per liter will yield good 
engine life- 5,000 hours. This is about 200 hp for the turbo charged DD671. 
Older engines should be run lower, maybe 20 hp per liter. This is about 120 
hp for the venerable Ford Lehman. This implies that the Lehman can be run at 
near WOT, but see below for speed related wear.

The other factor that wears out engines is piston feet per second, or 
indirectly rpm. Slow engines last longer than fast engines. Again modern 
engines with better materials and lubrication can be run faster than older 
engines. I believe a modern Yanmar can be run at 2,800 rpm all day long, but 
a Lehman should be limited to about 2,000.

In so far as running slow, the consensus on boatdiesel is that if the engine 
is run fast enough to produce enough power for all systems to get up to 
operating temperature (and there is some debate about coolant temperature 
versus oil temperature) then you will not harm your engine. My 370 hp Yanmar 
will get to full operating temperatures at 1,500 rpm or better. To be on the 
safe side, I run at high power for a few minutes after a long, slow cruise.


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