1997 polo overheats even after removing thermostat

On a water cooled engine... the impeller on the water pump is no longer working correctly. It has probably come loose from the input shaft and is no longer pumping water. You can prove this on a warm engine by filling the radiator to the top and then accelerating / decelerating the engine... if you don't get a change in the water level the water pump is shot.

Kelly

I am not familar with your specific car but if it overheats after the thermostat make sure the coolant level is full. Some cars can hold qiuite a bit of air in the cooling system. Open the radiator cap and slowly add a 50/50 water/coolant mixture until the radiator is full. With the heater level switched to hot, start the car and watch and see if the coolant level drops it may take a while for the air to move out. If the coolant level is full but it continues to overheat then I would suspect the water pump is not moveing the coolant thru the system or the electrical cooling fans (assuming you have them) are not coming on. If the car has electrical cooling fans and they are not coming on when the car is over heating you may have a sensor problem or an power problem. If the electrical cooling fans turn on but the car overheats although the coolant level is full I's suspect the water pump and/or a radiator that needs to be flushed.