Moving the water heater from the heat exchanger
line to the thermostat by-pass increased my steady state (over two hours) top speed by close to 20%. see
http://www.sankaty.homestead.com/speed.html
For more details on how to change it see
http://www.sankaty.homestead.com/waterheatercircuituniversal5432.html
My engine is a 1980'' 32HP Universal 5432 that is very similar to the Westerbeke M40 of the 1980''s.