A vane-type water pump mounted on the front side of the cylinder block circulates coolant through the engine. The flow of coolant washes each of their cylinders and is directed to the rear of the engine. Block-molded coolant galleries direct coolant flow around the intake manifold and exhaust manifold ports, spark plugs, and exhaust valve guides.
The hard wax thermostat is built into the bottom hose on M10 engines, housed at the front of the engine on M20 and M30 engines, or behind the knee under the top timing belt cover (on the front side of the cylinder head) on M40 engines. During engine warm-up, a closed thermostat prevents coolant from circulating through the radiator. When the engine temperature approaches normal operating temperature, the thermostat opens and allows hot coolant to circulate through the radiator where it is cooled and returned to the engine.
The pressure in the cooling system raises the boiling point of the coolant and increases the efficiency of the radiator. Sealing of system is provided with a special tight cover. If the pressure in the system reaches a certain value, it acts on a spring valve inside the cover, which opens and allows excess coolant to flow out through the overflow pipe.
The sealed cap on models with four-cylinder engines is located on the upper side of the radiator; on six-cylinder engines, it is located at the top of the transparent plastic expansion tank. Lid tightness indicators are indicated on the lid itself. Usually they are 1.0 bar or 1.2 bar.
Do not remove the sealed cap from the radiator or expansion tank until the engine has completely cooled down and the pressure in the cooling system has been completely relieved. Removing the cover when the engine is hot can cause severe burns.