The circulation of the coolant. Mercedes-Benz E-Class

Fig. 5.25. Scheme coolant gasoline engine: A - the thermostat is closed, the fluid is circulated in the engine in the small loop at a temperature below +85 ?� C (+87 ?� C); In - the thermostat is partially open, fluid circulates in the small and large loops at a temperature of 85 (+87) to +94 ?� C (+102 ?� C); C - the thermostat is fully open, the fluid circulates through a large circuit through the radiator at a temperature above +94 ?� C (+102 ?� C); 1 - the block of cylinders; 2 - cylinder head; 3 - the coolant pump; 4 - thermostat; 5 - the bottom nozzle of the cooling system; 6 - the upper outlet of the cooling system; 7 - a radiator; 8 - a connecting pipe; 9 - a connection for the air outlet; 10 - expansion tank; 11 - float; 12 - cistern; 13 - a branch pipe for supplying coolant to the radiator heater; 14 - inlet coolant from the radiator heater right; 15 - a heater radiator; 16 - inlet coolant from the radiator heater left; 17 - oil cooler

After starting a cold engine coolant is circulated in a small circle, which is limited to the engine cooling water jacket and the radiator heater (Fig. 5.25). The thermostat remains closed while the engine warms up to operating temperature.

The amount of cooling fluid circulating in the small circle is smaller, so the engine quickly reaches operating temperature. Then the thermostat opens and the hot coolant to circulate through the radiator downward. The heat sink as a result of blowing air counter flow heat from the engine diverted into the atmosphere. The thermostat controls the temperature of the coolant, preventing the motor from overheating and cooling.

The coolant is supplied directly back to the engine. So it quickly heats up, providing warming up the engine. The radiator is connected only when the coolant reaches a certain temperature. The thermostat opens, the cold fluid exiting the outer loop, gradually mixed with the heated water from the small loop. This prevents the so-called cold shock of the engine.

Once the coolant temperature begins to rise, the thermostat opens and fluid begins to circulate through the large circuit simultaneously closes small contour. At an operating temperature coolant is circulated through the bottom hose from the left tank of a radiator to the water pump, which pumps fluid in the engine block, oil cooler and the cylinder head. Most of the liquid and then through the open thermostat on the upper hose is fed back to the right of the radiator tank, the other part at this time is supplied to the radiator heater car. Springing from the bottom of the radiator fluid is cooled by passing the engine warms up and gets on top of the radiator. When passing through the radiator cools the hot liquid. When driving the coolant temperature falls below the operating temperature, the thermostat again closes the passage through the radiator until the coolant is heated to the desired operating temperature.

To improve the cooling efficiency of the radiator fan speed can be increased through the use of viscous coupling or, depending on the configuration, the blower motor. When off, fan clutch rotates at the same rpm as the engine crankshaft, but no faster than 1000 min ^-1. A viscous clutch or the fan unit is switched on or bimetallic switch in thermal switch if the coolant temperature exceeds a certain value. Turns off the fan when the coolant temperature falls below operating.