Coolant circuit function

W20.00-1073-76

General

The engines have a closed engine cooling system (pressurized system). The coolant in the engine cooling system, which is brought into circulation by the coolant pump (1.2), absorbs the heat of the hot engine component parts. When the engine has reached its operating temperature, the heat is delivered into the outside air via a cooler.

Engine cooling circuit

The coolant pump (1.2) is belt driven. If the engine and is running and has not yet reached its operating temperature, the coolant circulates within the engine. For vehicles with a regulated coolant pump (1.2), the rpm of the coolant pump (1.2) is permanently regulated. The engine management (MCM) control unit (A4) reads in the signals of the coolant pump rpm sensor (B640) and continuously regulates the delivery rate of the coolant pump (1.2). For this purpose, the engine management (MCM) control unit (A4) actuates the coolant pump solenoid valve (Y631).

Because the coolant thermostat (1.1) is usually closed when the engine is cold, the coolant flows via the coolant short circuit duct into the oil/coolant module (1) and, from there, it is led past the closed coolant thermostat (1.1) and through the coolant pump (1.2) to the heat exchanger (oil-water).

If the temperature of the engine oil is more than 115 °C (opening temperature of the oil thermostat), it is cooled via the heat exchanger (oil-water) so that it does not exceed the temperature of 120 °C. The heat exchanger (oil-water) is fastened to the oil/coolant module (1), and projects into the crankcase.

In this way, the coolant gets into the crankcase and, therefore, reaches the cylinder liners (2). At the same time, part of the coolant is led to the fuel cooler (8) and to the compressor (9) and, via separate feed lines, to the exhaust gas recirculation cooler (6) and to the exhaust gas recirculation positioner (Y621).

From the fuel cooler (8) and from the compressor (9), the coolant comes directly back to the coolant pump (1.2).

The coolant delivered to the cylinder liners (2) flows further to the cylinder head (3).

The cylinder head (3) has a split coolant jacket. This means that the coolant, after flushing the cylinders, flows both on the inlet side and the outlet side in the cylinder head (3). In the cylinder head (3), the coolant first gets into the bottom cooling level where it flushes the fuel injectors and valve seat rings.

Finally, the coolant flows to the upper cooling level and cools the valve guides located there.

Afterward, the coolant is led outward into the coolant pipe manifold (4), into which the coolant from the exhaust gas recirculation cooler (6) and the coolant from the exhaust gas recirculation positioner (Y621) is also led.

From the coolant pipe manifold (4), the coolant, via the coolant short circuit duct and the still closed coolant thermostat (1.1), comes back into the oil/coolant module (1) and the coolant pump (1.2) until the operating temperature of the engine is reached.

If the operating temperature of the engine is reached, the cooler circuit is also switched on when the coolant thermostat (1.1) is opened.

Depending on the position of the coolant thermostat (1.1), more or less coolant now flows through the vehicle cooler directly via the coolant short circuit line to the coolant pump (1.2). The temperature of the coolant in the coolant circuit is regulated in this way.

The fan (12) is used to increase the vehicle cooler's cooling output.

During this process, the temperature of the coolant is constantly monitored via the outlet coolant temperature sensor (B606) and the inlet coolant temperature sensor (B607), which are both read in by the engine management (MCM) control unit (A4).

The various pressures in the engine cooling system which arise due to the temperature fluctuations are balanced out over the coolant expansion reservoir.

Cooling of the nozzle unit (5) for the regeneration of the DPF (only for engine version Euro VI Standard)

The coolant for cooling the nozzle unit (5) is removed from the exhaust gas recirculation cooler (6). Then, it is led via the nozzle unit (5), in which the injection nozzle is located, and led back into the coolant pipe manifold (4).

AdBlue® heater

The coolant for the AdBlue® heating is also removed from the coolant pipe manifold (4). During actuation of the AdBlue® heating coolant solenoid valve (Y627), the coolant is led via the hose package to the AdBlue® container and, from there, is led back into the oil/coolant module (1).