Electrically piloted thermostat????

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Jan 7, 2014
Slimy Mudhole
What does that mean??

My Peugeot 207 1.6 is acting up as I get an overheating alarm but the car is totally cold, checking in other forums it seems that is a common fault of the temperature sensor or of the thermostat, I back probed the sensor and it gives a reading of 11 mega ohms and the resistance drops as the temperature rises.

On the same connector of the temperature sensor is an "electrically piloted thermostat" in terminals 1 and 2 but I never encountered such an animal before, so I envision two options:

1.- this thing is a normal thermostat that informs the computer about his state via a change in resistance. Or

2.- The computer controls the thermostat at its pleasure via a solenoid, meaning that if I apply voltage to the terminals , I will open the thermostat??

I back probed it and it gives a reading of 9.2 ohms so it could be shorted or it could be a solenoid. So I don't know if either of them are dead for sure.

Any of you have encountered something like this?? If it helps this is the same engine as the second generation Mini Cooper.

In the pic is the symbol of the connector, terminals 1 and 2 are of the electrically piloted thermostat and in 3 and 4 is the coolant temperature sensor.

Thanks in advance for any help .
Since your Peugeot shares an engine with the BMW Mini it's likely safe to assume #2.

BMW's product line is rich with electrically-operated, computer-controlled thermostats. If you have access to a diagnostic code reader, you may find a code is set for a faulty thermostat.
Well I tried an Autel scantool and a VCDS in generic OBD mode and neither of them could talk to the car, then I borrowed the factory tool and found a "Temperature sensor implausible signal" code but nothing about the thermostat.

But since the temperature sensor and the thermostat are in the same housing, I ordered a new thermostat housing and replaced it.

Now the car is back to its former self but I think the jury is still out on how the thermostat works in this engine. In the "Test of actuators" section of the scantool I couldn't find anything about the thermostat and I put the old thermostat in boiling water but it did not open. Although the water here boils at 90°C (194°F) so maybe it wasn't hot enough to open.

The "piloted" part of the thermostat would suggest that it is computer controlled but maybe is a mistranslation from the French.
Probably the computer controls the thermostat. My Cruze does the same thing. An aftermarket tune I did dropped the temperature by 20*F. It'll drop even lower if needed, such as during very spirited driving on a track.
My Mercedes has something similar to this (not sure if it's exactly the same), but I know how it works.

It has a normal wax pellet type thermostat, but it is set to open at a very high temperature of 110 C by itself. It also has a "heater" built into the thermostat so that the car can "fool" the thermostat into opening a lot earlier. According to the service manual, the car can decide to open the thermostat anywhere from 80 C to 110 C, although I personally have only ever seen a variation from 85-95 C in the driving that I do.

So, if I were to put my thermostat in boiling water, it wouldn't open. But in the car, with the electric heating element working, it can open as early as 80C.
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