Engine Cooling Pie Chart
Where Does All the Heat of Combustion Go?
The heat in the engine room is just 7% of the total heat generated by combustion. 33% goes into turning the crankshaft. And if the heat of combustion is not removed, the engine seizes and dies.
from page 57 Marine Diesel Basics 1
Purpose of the Cooling System
However, the purpose of the cooling system is MORE than merely removing excess heat to avoid failure. The primary purpose of the cooling system is to keep an engine within its optimal temperature range. This maximizes fuel efficiency and minimizes carbon build-up and excess wear.
Conversely, an engine running too cold suffers reduced performance and carbon build-up, causing long-term damage and shorter engine life. (This can happen if the thermostat sticks open or is removed.)