Cooling passages are located Inside the heat exchanger or radiator. The passages increase the mechanical advantage of the heat exchanger by increasing the surface area in contact with ambient air. The cooling passages within the heat exchanger increase efficiency but they can become plugged from metal debris chaffing away from the engine block as the metal wears and flakes away from it; or it can become restricted from the outside ports becoming blocked from environmental contamination like dirt or trash.

It is important to maintain the cooling system by replacing the coolant and cleaning the fins of the radiator using air pressure or cooling fin rods to achieve proper heat exchange.

The thermostat is a a devise that opens and closes based on a reaction to the temperature to a heated wax element pushing against a rod withing a confined chamber. Heat expands a wax element that is calibrated to open at a specific temperature, and remain closed until the desired temperature is reached.

A thermostat allows the engine to achieve operating temperature quickly by preventing fluid exchange to take place. The thermostat blocks coolant recirculation until operating temperature is achieved. When a cooling system is operated without coolant recirculation it will overheat. The upper radiator hose will remain hot and the lower radiator hose will remain cold regardless of engine operating temperature. Inspecting the engine temperature with a pyrometer and inspecting the temperature of the radiator hoses when the expected cylinder head temperature is achieved is an excellent way to determine if the thermostat is opening.