2018 MK8 1.0 St Line

Ever since the weather turned cold (2 weeks) on a morning I start the car and I get a red box on screen saying ' engine coolant over temperature ' fans ramp up to full, turn car off straight away, restart it and it's normal and I can drive to work (only seems to do this on a morning). If it happens 2 mornings in a row you get a engine light on which you can clear with forscan.

I bought a replacement sensor Facet model FAC7.3285 and placed it onto the connector last night (didn't fit it to car) started it up this morning as it's cold again and it did it again, which kind of tells me it's something at the other end of wherever it connects maybe.

The new sensor measures 62kohm when cold which I think must be normal, i will confirm tomorrow on old one tomorrow as it won't do it again now rest of the day.

After turning car off and on again, don't get the error again, engine temperatures all read fine as well. 

Any other help, or things to check would be greatly appreciated.

 

Did a pre start test, today with forscan engine coolant measures 12degrees which for today seems to be correct.

Problem is I cant do a non start test because forscan requires the ignition on and as soon as I do that I get the warning.

Open to suggestions if anyone can help

Ok I've sorted this, will post the solution just in case anyone comes in future searching. So I was looking through the DTC data for PCM module and noticed the Intake Air Temperature was reading -27 degrees when the car started which is obviously incorrect. Then it clicked. 2 weeks ago whilst trying to investigate a boost surge issue no one on the internet seems to have an answer for I replaced the IAT near the air filter. At the time I thought it didn't look genuine so kept the original,  measured the fake one and the old one and they are massively different. I swapped back to the old genuine ford sensor and boom... DTC and message on screen have vanished. Here's a photo of the fake one and genuine one for comparison. The fake one has a much smaller blue sensor bead.

 

This is the fake 'Lucas' eBay one 

And this is the genuine ford one, not sure of brand but it's very obviously better made.