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Old 07-30-2020, 08:57 AM   #1
fryedaze
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City: Solomons Island Md
Vessel Name: Fryedaze
Vessel Model: MC 42 (Overseas Co) Monk 42
Join Date: Sep 2011
Posts: 1,721
Thermostat Cummins 6BT5.9M 210 HP (1989)

Our engines have always had inadequate cooling. It is a design flaw in the early Cummins 6BT engines. The boat runs 180-190F in warm (75-80F) water at 1500 rpm. It will not run at 2500 rpm for more that a few minutes without going over 205F and continuing to climb. 2600 rpm is WOT. Previously I have increase fitting sizes and hoses on some of the recommendations from Tony at SBMAR. I came across an article he wrote about the older Cummins cooling issues an it recommended a larger opening 160F thermostat that they had developed. I installed them last week. The new cooling performance is very good. I now cruise at around 170F at 1500 rpm. I ran at 2500 rpm for an extended period of time and the temps stayed below 200F. Previously I had to focus on the temp gauges hovering around 200F anytime I went above 2000 rpm to catch a bridge opening. This is one of those "I should have done this 10 years ago" moments. The old thermostats were 180F, stamped 6/1988.
Just sharing
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Dave Frye
Fryedaze, MC 42 (Monk 42') 1989 Overseas Co
https://mvfryedaze.blogspot.com/
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