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Old 11-10-2015, 12:53 PM   #52
Cuttyhunk47
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City: Louisville, KY
Vessel Name: Jessie
Vessel Model: 43' Marine Trader 49' Albin Tricabin
Join Date: Nov 2015
Posts: 97
I would like everyone's (or anyone's) opinion on what is too low an rpm for diesel engines. Do I understand it that manufacturers set a suggested cruising speed at around 75-80% of WOT? I realize that there is a minimum temperature required to burn the fuel completely, but is temperature the only restriction? On the following engine for example:
Detroit Diesel 12V71N
WOT is 2300 rpm and fuel burn is 28 gph
at 78% (cruising speed) rpm is 1800 rpm with a fuel burn of 14 gph
at 52% rpm is 1200 rpm with a fuel burn of 6 gph

My question is, if the engine temperature stays above 150 or so, can you cruise at 1200 rpm without damaging the engines? I'm asking about long term damage if you chose to cruise at these reduced speeds throughout the life of the engine. Obviously, you would need to blow them out for a few minutes periodically throughout each cruise.
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