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Clio Mk2 - Low coolant temperature issue - electrical?

  Clio II
Hi guys!

Does anyone have an idea if there is an electrical issue that can interfere with the coolant sensor readings, ie too low, and how to diagnose it?

The story...

Have an older Clio Mk2 (1.2 16V) that has developed a temperature issue (2006, although with only about 30000 miles on it).

The coolant temp has always been dead centre (4 pins) but recently it started getting stuck on 2 pins, ie too low.
So I took to the internet and the common suggestion was that it was either the thermostat or the sensor, so I ordered and changed both.
Aftermarket stuff, the thermostat was of Calorstat brand for instance, not very expensive. :)

But the issue remained.

I measured the temperature from ODB2, and it seems to level out at around 77 degrees Celsius when driving.
I checked the hose from the thermostat to the cooler, and it stays cool until about the temperature above, then it gets plenty hot.
If it's hot enough I cannot say only by touch though, I can grip it, but only just.
So the stat wasn't stuck, it just seemed to open too soon, although it is spec'ed to open at 89 degrees.

Having read a lot that the cheap aftermarket stuff can be bit of hit and miss, I just ordered another thermostat, a Febi one, which should be better (and pricier) quality, right?
But guess what.... Opening the Febi box revealed a Calorstat stat identical to the one I got... For double the price... Oh, the joy... :rolleyes:

Oh well, I switched the thermostat anyway, and.... the issue remains.

Given that it had the same symptoms before I changed anything, I suspect there problem is electrical, that the sensor reports too low temperature (ie higher resistance than it should).

But I don't know how to diagnose this. The Haynes manual doesn't really say either, only to test if the sensor is broken. Anyone?

Many thanks from Sweden! :)
  Clio 2 1.2 16V SE
Are you helped already as this is a older post? You can test the sensor if it’s working in boiling water! When u plug it in the engine temperature should go sky rocket and the van also should kick in and start spinning
  Clio II
@HetZwaantje9 No, not yet. :)

I have checked the old and the "new" (the one I bought first) stat and they both seem to open correctly at around 90c.

I guess I can take out the new sensor and check the temperature readings and perhaps compare it with the old one as well. Although I don't if that says anything, as the old sensor also reported the wrong temp.

I started to suspect something electrical, eg poor ground or something. I just have to get around to do some measuring some day :)