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6.3.1. Circulation of cooling liquid

Fig. 5.25. Scheme of circulation of cooling liquid of the petrol engine: And — the thermostat is closed, liquid circulates in the engine on a small contour at a temperature below +85 °C (+87 °C); In – the thermostat is partially open, liquid circulates on small and big contours at a temperature from +85 (+87) up to +94 °C (+102 °C); With — the thermostat is completely open, liquid circulates on a big contour, through a radiator, at a temperature more than +94 °C (+102 °C); 1 – block of cylinders; 2 – block head; 3 – pump of cooling liquid; 4 – thermostat; 5 – lower branch pipe of the cooling system; 6 – top branch pipe of the cooling system; 7 – radiator; 8 – connecting branch pipe; 9 – a branch pipe for an air outlet; 10 – broad tank; 11 – float; 12 – drain tank; 13 – a branch pipe of a supply of cooling liquid to a heater radiator; 14 – a branch pipe of removal of cooling liquid from a heater radiator right; 15 – heater radiator; 16 – a branch pipe of removal of cooling liquid from a heater radiator left; 17 – oil heater

After launch of the cold engine cooling liquid circulates on a small circle which is limited to a water shirt of cooling of the engine and a radiator of a heater (fig. 5.25). The thermostat remains closed until the engine heats up to working temperature.
In a small contour the thermostat bars the way of liquid to a radiator.
The amount of the cooling liquid circulating on a small circle is, less, therefore the engine reaches working temperature quicker. Then the thermostat opens, and hot cooling liquid begins to circulate through a radiator from top to down. In a radiator as a result of its obduv heat from the engine is taken away by a counter flow of air in the atmosphere. The thermostat regulates temperature of cooling liquid, protecting the engine from an overheat and cooling.
Cooling liquid directly moves back in the engine. So it heats up quicker, providing an engine warming up. The radiator is connected only when cooling liquid reaches a certain temperature. The thermostat opens, the cold liquid which is coming out an external contour gradually mixes up with heated water from a small contour. It prevents so-called cold shock of the engine.
As soon as temperature of cooling liquid begins to rise, the thermostat opens, and liquid begins to circulate on a big contour, the small contour is at the same time closed. At a working temperature cooling liquid circulates on the lower hose from the left tank of a radiator to the water pump which forces liquid in the engine block, the oil heater and a head of cylinders. The most part of liquid then via the open thermostat on the top hose moves back, to the right tank of a radiator, other part moves in a radiator of a heater of interior of the car at this time. The cooled liquid following from below from a radiator, passing the engine, it is warmed and gets to a radiator from above. At pass through a radiator hot liquid is cooled. If at the movement of the car temperature of cooling liquid falls below working temperature, the thermostat blocks pass through a radiator that that time again until cooling liquid heats up to necessary working temperature.
For increase in efficiency of cooling of a radiator the frequency of rotation of the fan can be increased due to use of the viscous coupling or, depending on a complete set, the electric fan. At the switched-off coupling the fan rotates with the same turns, as a bent shaft of the engine, but not quicker than 1000 min.-1. The viscous coupling or the electric fan turn on from the bimetallic switch or a thermoswitch in case temperature of cooling liquid exceeds a certain value. The fan when temperature of cooling liquid falls below the worker is switched-off.

The electric fan of a radiator can turn on also at the switched-off ignition because of aerodynamic heating of the engine.