I have a 2000 reg Lupo. Recently been overheating on me, changed the coolant sensor last week and everything ran smooth after that for around 2/3 hours then it’s started overheating again. Now today have just flushed the coolant and re-filled it and it’s still overheating after about 5 minutes of driving? please anyone with any advice is much appreciated, also my heater fan blows cold inside the car if this has anything to do with the issue?