Hi everyone, I’m sure this topic has been dealt with previously but I can’t find anything on it. I have a 1998 1.8 executive and the engine temp gauge is always on cold when driving, when the car is just idling it seems to go up and the heaters inside don’t seem to be blowing very hot air either while driving but they get hot when idling. Is this just a sensor issue? The other day I drove in excess of 25 miles down the motorway and the temp gauge was always on its lowest mark. Any advice would be much appreciated. Thank you everyone.

I would suspect the thermostat.

This happens if you remove the thermostat from the car, the coolant overcools and the car cosume alot of fuel.
I've played a bit like that with some cars to find other problems, but they act just like you described.
So two hands for faulty thermostat(or completely missing).
The sensor is probably ok. It is measuring and sending info to the dash.
If it fails, it didn't work at all, or it stops when engine is hot.

Yep agree, probably a thermostat either sticking in the open position or missing completely. Easy to access and very cheap to replace.
I took a picture of the one I removed from a BA 1.5:

Not sure if it matters too much what the operating temperature is, just so long as it work!