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Thermal Management, Function - GF07.10-P-1012MRH

Engine 274.9 in model 205.047/053/054/147/247/253 

Engine 274.9 in model 253.353/953 

Engine 274.9 in model 253.354/954 

Function requirements for thermal management, general points 

Thermal management, general 

The coolant temperature of the Engine is regulated with the thermal management controlled by the ME-SFI control unit (N3/10). The following advantages arise from this:

The controlling of the thermal management is dependent on the following sensors and signals:

G14547245Courtesy of MERCEDES-BENZ USA

Schematic diagram 

Function sequence for thermal management 

The thermal management is described in the following points:

Function sequence for post-start phase with electric coolant pump 

In the post-start phase the coolant circulation has an open circuit through cutout of the electric coolant pump. Here the electric coolant pump is not actuated by the ME-SFI [ME] control unit. Due to missing cooling the Engine warms quicker and the exhaust emission are reduced.

The electric coolant pump is switched off for a cold start if the following conditions are fulfilled:

Based on the "heat" request, the electric coolant pump switches on and as a result the vehicle interior is heated quickly.

View of electric coolant pump 

G14547246Courtesy of MERCEDES-BENZ USA

If the conditions for shutoff of the electric coolant pump are no longer fulfilled, the ME-SFI [ME] control unit stops actuation of the electric coolant pump. The electric coolant pump is therefore switched on and the coolant circulation is achieved again.

Function sequence for coolant thermostat regulation 

Opening and closing of the ball rotary slide in the coolant thermostat occurs through the temperature-influenced elongation or contraction of the expansion wax element in a temperature range of about 98°C up to 108°C.

Additionally opening and closing of the coolant thermostat is performed variably and dependent on the motor requests dependent on actuation of the coolant thermostat heating element (R48).

To do this the ME-SFI [ME] control unit actuates coolant thermostat heating element by means of a ground signal dependent on the operating conditions. The power supply takers place over "circuit 87 M2".

The coolant thermostat can take on the following positions:

Closed 

The ball rotary slide of the coolant thermostat is closed if the following conditions are fulfilled:

In this position the coolant flows through the Engine circuit and the heater heat exchanger as required. The Engine radiator is not integrated in the coolant circuit. The coolant is heated more quickly in this way.

Through rapid warming the Engine reaches its operating temperature quicker which is favorable for fuel consumption and emissions.

Open (mixed-fuel mode) 

The ball rotary slide begins to open if one of the following conditions is fulfilled:

In a temperature range of the coolant of about 98°C up to 108°C or according to energization of the coolant thermostat heating element, the expanding wax element begins to expand and actuates the ball rotary valve. This releases the connection to the Engine radiator. The opening cross-section of the ball rotary slide is adapted according to the temperature of the expanding wax element or the coolant temperature. In this way the volumetric flow rate of coolant to the Engine radiator can be varied.

View of coolant thermostat closed 

G14547247Courtesy of MERCEDES-BENZ USA

Open (cooler operation) 

For exceeding of a coolant temperature of about 108°C the ball rotary slide is opened completely and the coolant can flow unheeded over the Engine radiator.

At a coolant temperature > 85°C and full load request, the ball rotary valve also fully opens due to the heating of the wax expansion element.

The coolant temperature is lowered under the following conditions to prevent a critical temperature range arising:

The coolant temperature is, in this connection, lowered depending on the outside temperature by heating the wax expansion element (for an outside temperature < 12°C up to approx. 90°C and for an outside temperature > 12°C up to approx. 80°C).

View of the coolant thermostat opened 

G14547248Courtesy of MERCEDES-BENZ USA

Function sequence for overheating protection 

In a case of thermal overload the overheating protection protects the catalytic converters against Engine damage and overheating damage.

The following measures are taken for overheating protection:

IMPORTANT A warning message in the instrument cluster is shown for an excessively high coolant temperature. To do this the ME-SFI [ME] control unit transmits a corresponding signal via the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and via the user interface CAN to the instrument cluster.

The powertrain control unit reads in the temperature in the low-temperature circuit via the low-temperature circuit temperature sensor (B10/13). In this way the coolant temperature in the low-temperature circuit is detected.

Function sequence for fan control 

The powertrain control unit actuates the fan motor (M4/7). Here the actuation occurs via the drivetrain-LIN (LIN C3) and all rotational speeds between 0 and 100% can be adjusted. For faulty actuation the fan motor rotates at its maximum rotational speed (fan emergency mode).

The climate control control unit transmits the status of the A/C to the interior CAN over the electronic ignition lock control unit, the chassis-FlexRay to the powertrain control unit and via the drive train CAN to the ME-SFI [ME] control unit.

Delayed fan switch off 

The fan motor runs on for "ignition OFF" for up to 6 minutes if the coolant temperature or the Engine oil temperature has exceeded the prescribed maximum values. If the battery voltage drops down a lot, the delayed fan switch off is suppressed.

Function sequence for radiator trim flaps (with CODE 5U3 (AIRPANEL)) 

To lower the fuel consumption (via a lower aerodynamic drag), the radiator trim flaps are closed. This also causes reduced Engine compartment cooling off and a dampening of Engine external noise emissions to the outside. The radiator trim flaps are opened under the following preconditions:

The radiator trim flap actuator motor (M2/37) is actuated by the powertrain control unit via the drivetrain-LIN. The radiator trim flaps are closed when the conditions are no longer fulfilled or the Engine is off.

IMPORTANT Due to the spring preload of the actuator motor, the radiator trim flaps are opened suddenly with a perceivable noise in the case of a malfunction (limp-home function).

IMPORTANT Cleaning position

Turn the key in the ignition lock to position 2 (Engine not have started). The radiator trim flap opens itself after about 120 s.

Function sequence for charge air cooling 

The charge air cooler is connected to the low-temperature circuit. If the charge air temperature is>35°C, the low-temperature circuit circulation pump 1 (M43/6) will be actuated by the powertrain control unit and via the drivetrain LIN. If the charge air temperature falls below 25°C, the low-temperature circuit circulation pump 1 is switched off again.

The charge air temperature is detected in the charge air distributor by the charge air temperature sensor upstream of the throttle valve and the charge air temperature sensor downstream of the throttle valve and sent to the CDI control unit using a voltage signal.

In the low-temperature circuit the temperature control of the charge air cooler takes place over the low-temperature circuit switchover valve (Y73/1). According to ambient conditions the charge air cooler is regulated over the coolant quantity in the low-temperature circuit through the low-temperature circuit switchover valve. The low temperature circuit switchover valve receives the actuation for this from the powertrain control unit via drivetrain LIN. Feedback of the position from the low-temperature circuit switchover valve takes place via the drivetrain LIN to the powertrain control unit.

IMPORTANT Only open the cap on the low-temperature circuit when the charge air temperature is increased (lack of power) and the Engine is cold.

The refrigerant must reach up to the cap.

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