The top of the Cylinder Head has a recess for the Thermostat (8/53). The coolant flow is held back until the Thermostat starts to open at approximately 170 degrees F.
 
As long as the Thermostat is closed, the excess flow will bypass the Cylinder and Cylinder Head, and go directly to the Reservoir (8/56) through the Bypass Hose (15/19).

When the Thermostat opens, the Cylinder and Cylinder Head flow goes through the thermostat and into the Reservoir, where it joins the bypass flow. From there the warm coolant returns to the Heat Exchanger (hose 16/16) where the accumulated heat is transferred to the raw water.

The closed loop cooling system has been charged, at the factory, with a 50/50 mixture of fresh water and permanent anti-freeze. The Reservoir (8/54), was specially designed to prevent over filling. The correct level is to the bottom of the threads. We recommend checking the level each time the oil is changed.