Hopefully i can help..
There is plastic coolant flange on the side of the cylinder head "the opposite side to your timing belt" if you follow the large rad hose upto it..you'll note there will be or should be sensor located on it,usually green or blue in colour.ive included diagram below of a 1.8T red arrow sensor/yellow thermostat.normally these sensors are just push fit after you put the new o ring on and held in place with the circlip you need to pop/slide back in to hold in place..you notice that with the old one still on the car..with a flat head screwdriver pop the circlip out and pull the sensor out and refit with the new o-ring/clip in reversal of removal ... But yeah problems like that can be normally down to just that sensor itself so would be worth while replacing that..or a stuck thermostat can be quite common..but make sure the new sensor has the new o-ring and circlip
thank you, ***** ***** been nice to see engine in car, showing where sensors are , not engine out with nothing to tell front or back, and everything missing off it. Y ou are mechanic,and understand , I dont, which is why i spend £15.00 for your help, photo of not much help. I sked how many coolent sensors ,you show two arrows yellow and red I understand red but is yellow another sensor I must change.
well givin even showing a picture of the engine you wouldnt see the sensor anyway nor the thermostat "yellow arrow" - there is only 1 sensor the one located in the red arrow" you see the green sensor on that engien above? that the sensor you need to look for - if there was more then one then i would of added that above - the photo there is more than helpful because just looking at the engine i would only be able to tell you which side it was on.. With the engine out it will give more of an idea what you need to look for on the engine itself - rather then just top view of it and a general area to check.. if you see where im coming from.... you know what side the gearbox is on.. then that side of the engine is where you need to look..follow the large coolant hoses up that side - you come to the coolant flange housing that sensor is on...thats what the picture above is angled at - the yellow arrow is you thermostat location..not really the best of jobs to get to..but trying the sensor being easier to get to is best place to start... if you want to send a picture of your engine in to me using the "paperclip icon on your message box" then you can do that..