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Coolant pump in cars

Posted On December 3rd, 2019

The coolant pump provides forced circulation of the coolant in the cooling system. In some sources of information, the coolant pump is called a water pump, which is essentially untrue. Water has not been used as a coolant for a long time.


The pump is installed, as a rule, in front of the engine and can have two types of drive: mechanical and electric. A mechanical drive is made from a crankshaft or engine camshaft using a belt drive. The electric drive involves the installation of an electric motor with a control system.

Centrifugal pumps are used as a coolant pump. The design of such a pump includes an impeller mounted on a shaft with a pulley placed in the housing.

The pump housing is made of cast iron or cast aluminum. The housing has channels for supplying and discharging coolant to the impeller. Between the pump housing and the engine block is installed a sealing gasket and protecting against leakage of the coolant pump.

The impeller (commonly referred to as the impeller ) directly circulates the coolant. It is made in the form of blades of a special shape. The impeller is mounted on the drive shaft. The shaft is located in the housing with bearings. A drive pulley is installed on the opposite side of the shaft.

Coolant Pump Operation

When the impeller rotates, a vacuum is created at the pump inlet, due to which coolant from the radiator enters the pump. The liquid is supplied to the central part of the pump, moves along the blades and is discharged by centrifugal force to the outlet of the pump and further to the cooling jacket of the cylinder block.

Two cooling pumps can be installed in the cooling system – the primary and secondary. Depending on the design of the engine, the additional pump performs one of the functions:

  • additional engine cooling ( operation in countries with a hot climate );
  • ensuring the operation of an autonomous heater included in the engine cooling system;
  • exhaust gas cooling in the exhaust gas recirculation system;
  • turbocharger cooling on turbocharged engines;
  • pumping coolant after engine shutdown ( to prevent engine overheating after stopping ).

The additional coolant pump has, as a rule, an electric drive. The pump is included in the engine control system and, if necessary, turns on (off) at the signal of the electronic unit .

Some Volkswagen engines have a switchable coolant pump . The switched-off pump provides quick warm-up of the engine at start-up by shutting off the coolant supply until a temperature of 30 ° C is reached. In this case, the coolant is constantly in the engine and warms up much faster. In addition to heating, the use of a shut-off pump reduces fuel consumption.


The supply of coolant is interrupted by means of an annular diaphragm (damper), which closes the fluid path, while the impeller continues to rotate. The diaphragm is connected by levers to the membrane, which moves under the action of the vacuum. The cavity in front of the diaphragm is connected by a highway to the vacuum source – the intake manifold.

The vacuum channel blocks the control valve included in the engine control system. When it is opened, the diaphragm moves under the action of vacuum, the impeller of the pump is deactivated. When the valve closes, the diaphragm returns to its place under the action of the spring, and the diaphragm releases the impeller. The pump starts to run.


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