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Liquid Cooling


The liquid cooling should take up the engine heat through the coolant, and release it, through the radiator, (1) into the open. The engine temperature should ideally be very constant. The heating of the vehicle interior is achieved through the heat exchanger (7).

How it works

The circulation pump cooling helps to avoid component-critical temperatures in all parts of the engine. Also the cylinders which are not in the vicinity of the pump, are cooled to the same extent. The temperature of the coolant increases, from its entry into the cylinder block, until it reaches the cylinder head. Whereby, the water jackets of the cylinders only exist in the upper half, sometimes even, with a continuously upwards increasing cross section. The distribution is also controlled through the openings in the head gasket. The avoidance of both hot spots and of vapour-lock is important. A pump (6) transports coolant, in a process regulated by the thermostat (5), from heat sensitive points in the engine to the radiator (1). One or two fans (4), controlled a by thermo switch (3) provide, when required, for additional heat exchange. This process is only fully initiated when the engine is too hot and / or there is insufficient air flow, to avoid unnecessary energy losses and to maintain the operating temperature (as high as possible) of the internal combustion engine. Beforehand, the coolant circulates through the short circuit cycle (8). Diesel engines often need a supplementary heating (9).The liquid cooling system is operated at up to approx. 1 bar over-pressure (testing pressure max. 1.5 bar) to allow an operating temperature of the coolant of more than 100°C. This pressure is mostly controlled through two valves in the lid of the reservoir tank (2, figure 3 for trucks). If it rises too sharply, for the protection, e.g., of the radiator, it is bled off as air (pressure release valve). If there is a danger of too low pressure through cooling, outside air is sucked in (check valve). Together, both mostly form a double-strike valve.


This kind of cooling has a steadying effect on the cylinder block and provides, except in modern diesel engines, for effective heating in the interior.


Apart from the electronification of the cooling system, there is one more possibility for higher efficiency and less weight, the vaporisation cooling. The heat transmission is optimised using substantially less coolant through the two-fold changing of the aggregate state. The air-conditioning already functions on this principle, however, for the higher temperature level of the engine cooling and the special mixture of the coolant, this conversion is difficult. The operational safety must be maintained at all costs. 06/09