Diesel Question

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thaeni

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Sep 28, 2008
120
Hunter 33.5 Chicago
I have been told that a Diesel engine likes to be run hard and that
running at lower RPM's is not good for the engine. If that's the case why is
it at every truck stop the big rigs sit for hours and often times all night
at idle...It seems like the truckers never turn their engines off !
 
Dan Johnson

Dan Johnson

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Oct 14, 2005
2,191
1983 Hunter H34 North East, MD
Thaeni...

Many truck stops are now making truckers shut down their engines due to pollution issues. They are providing units that fit in their cab windows that provide heat/ac as well as aux power for their sleepers and "toys".

There's a big difference between a Yanmar or Universal and a Cummins or Detroit Diesel truck engine. Regular maintenance, dry exhausts with large stacks, long runs at highway speeds, etc. keeps them in better shape to idle for comparitively short periods of time.

I'm sure there are more experienced diesel guys that will jump in with a more detailed answer.
 
Capt Morgan

Capt Morgan

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Apr 25, 2012
16
Hunter 41AC Sassafras River, MD
go to red line!

It is true, the average sailboat diesel hates to run for 8 minutes (from the mooring till you hoist the main) at low or medium RPM. Its generally the same reason that most stand by generators with low hours are trash (they almost never are under a significant load).

My surveyor suggested that I try to run the diesel until its well warmed and that I should red line the engine for 2 to 3 minutes each time I have it out, making sure she holds the 3100 RPM she is designed for, that smoke is not overly generated, and that she heats up but does not overheat. NOTE: You need a cool down period after this also, don't be 100 yards off the dock when you slow down from top R's.

Additionally, my 41' Hunter AC has the upgrade 54 HP Yanmar, plenty of power, so if you came out with the factory with standard HP, you may want to pull back just a bit below the red line.
 
Dan Hill

Dan Hill

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Dec 16, 2006
353
Hunter 25.5 Cayuga Lake, NY
Many over the road rigs now add aux power units that maintain cab heat or ac, one brand I have worked on was powered by a 2 cyl yanmar, go figure huh.

The biggest reason to run your diesel hard is to dissipate any moisture or unburnt fuel from the oil.

Low rpm idling causes "fuel wash" of the cylinder walls which is the washing away of needed lubricants causing excessive wear. Most truck owners bump their idle up to 1000-1200 rpms when sitting to help reduce this issue.

So, run her hard and up to full temps and don't forget as stated earlier by another to let her cool down a bit before shutdown.
 
garymckin

garymckin

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Mar 19, 2010
30
Hunter 1997 376 Ventura, CA
Diesel engines like to run under load other than free running. So when you are running under power keep it close to full power it will run better the next time you need it. Also keep up the maintenance of your engine.
Gary
P.S. Every day above ground is a good day.
 
Serge Tremblay

Serge Tremblay

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Dec 25, 2012
13
Hunter 40.5 Bermuda
I own a hunter 40.5 built in 96, Yanmar 50hp has 1400 hours was serviced every year, it starts and runs great with no load but has no guts at all when under load, I've checked exaust manifold and several other items but it remains gutless no tork at all, if alternator is ingaged I can't even leave the dock, I end up turning the key off to get the reaves up, anybody experience this that could point me in the right derection?
Sorry for butting in didn't know how to post my own!!
 
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