Just recently I have noticed that my petrol gauge shoots right past full in cold weather when the engine starts and then when switching off it will go just above empty. The following day when running it on a warmer day it went back to normal.

Hello Jaime, the signal from the fuel sender unit in the tank is via a variable resistor. When the tank is empty the resistance is very high (almost open circuit), and when the tank is full the resistance is very low (almost short circuit). I've not had any dealings with your model but it would suggest that the wire to the gauge is in some way being connected to the vehicle ground/body which causes the gauge to read more than full. Possible things to check would be the connector on the fuel tank to see if it is wet or if the wire is damaged and able to rub against the metal work of the car. Have you noticed if the gauge reads wrong if the car is wet, heavy rain, going through puddles ?

You can also use the built in dial sweep function of your instrument cluster to test the actual gauge which you try both when things are normal and when there is a fault.