Component description for the two disc thermostat heater element - GF20.10-P-3161AMG

ENGINE 156.980 in MODEL 164, 251 

ENGINE 156.982 in MODEL 209 

ENGINE 156.983 in MODEL 211, 219 

ENGINE 156.984 in MODEL 216, 221 

Location 

The heating element is located on two-disk thermostat housing.

Fig 1: Identifying Two-Disk Thermostat And Two-Disk Thermostat Element

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Task 

The heating element regulates the engine coolant temperature within the range from approx. 85°C to 105°C. From a coolant temperature of about 105°C the coolant thermostat opens independently of actuation (limp-home function).

By regulating the coolant temperature the following benefits result:

• Operating temperature is reached faster
• Reducing exhaust gas emissions
• Improved heat comfort.

Function 

Actuation of the heating element takes via a PWM signal (pulse width modulated signal) from the ME-SFI [ME] control unit (N3/10). The voltage is supplied through "terminal 87 M2e".

The open cross-section of the two-disk thermostat is determined via the duty cycle (frequency of the PWM signal).

The limp-home function ensures that the two-disk thermostat is completely opened above around 105°C, irrespective of actuation.

Function of two-disk thermostat, schematic 

Fig 2: Identifying Two-Disk Thermostat Function

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Short-circuit operation position (A) 

Heating element de-energized Coolant temperature < 100°C

Heating element energized Coolant temperature < 60°C

Mixed fuel operation position (C) 

Heating element de-energized Coolant temperature 100 to 115°C

Heating element energized Coolant temperature 60 to 100°C

Radiator operation position (C) 

Heating element de-energized Coolant temperature > 115°C

Heating element energized Coolant temperature > 100°C

Above about a 115°C coolant temperature the two-disk thermostat is fully open independently of energization (limp-home function).