2007 Peugeot 207 temperature gauge fluctuating

Tried replacing coolant temp sensor

replaced temp sensor, still has fault.

Could be thermostat , this explains if it's the TU3AE5 engine

207 Piloted Thermo.PNGIts role is to accelerate the engine temperature increase in order to improve the exhaust gas emission control and to obtain a higher engine operating temperature to reduce friction and fuel consumption.

The thermostat is open (whether in piloted or non-piloted mode if the temperature is above 105°C).

During normal operation, the thermostat is not piloted, it regulates the coolant temperature at 105°C.
207 Piloted Thermo B.PNG
For full engine loads:
The injection ECU controls the regulation of the thermostat at 89°C
The injection ECU controls the piloted thermostat heated resistor (26) in order to add the 16°C which the coolant lacks in order to melt the wax (25)
207 Piloted Thermo C.PNG
Time Operating Phase Description of the Operating Phase
t0 and t1 Partial load The engine management ECU does not activate the piloted thermostat regulation control.
The engine coolant temperature is regulated at 105°C guaranteeing a reduction in consumption
t1 and t2 Full load The engine management ECU detects a full engine load and controls the opening of the piloted thermostat by means of the internal resistor which melts the wax, simulating a temperature of 105°C.

The engine coolant temperature decreases and stabilises at a temperature of 89°C
t2 and t3 Full load The engine cooling is regulated at an engine coolant temperature of 89°C in order to avoid an excessively high engine operating temperature
t3 Partial load The engine management ECU detects a partial load and no longer controls the activation of the piloted thermostat internal resistor.

The piloted thermostat again regulates the engine coolant temperature of 105°C
The piloted thermostat opening control is determined in relation to the following parameters:
Vehicle speed (Guarantee of the performance of the engine cooling)
Intake air temperature (Guarantee of the performance of the engine cooling)
Ambient air temperature (Guarantee of the correct temperature under the bonnet in cold climates and of no adverse effect on the temperature in hot climates)
Engine load
Engine coolant temperature
Note: Bleeding of the cooling system uses a special injection ECU strategy.

Conditions necessary to inform the injection ECU of entry into a cooling system bleed phase:
Zero vehicle speed (For 10 seconds)
Engine speed above 1450 rpm (For 10 seconds)
Engine torque below 5 m.daN (For 10 seconds)
Example of the reference speed of a dual speed cooling fan unit (in %)
Graph.PNG
Key:
50% = Slow speed
100% = High speed
The piloted thermostat opening control is determined in relation to the following parameters:
Vehicle speed
Intake air temperature
Ambient air temperature
Engine load
Engine coolant temperature
The parameters of the cooling fan post-cooling triggering and duration map are set by the coolant temperature and the exhaust line temperature sensor.
The energy stored by the catalytic converter determines the activation of the cooling fan unit control.