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My VW Polo's coolant overflows out of the expansion tank. It's like there is too much pressure, causing the coolant to boil out of the tank, yet the temperature is normal.

The fan always kicks in, but after acceleration the coolant expands and overflows through the relief valve. When the engine is off, all the coolant is sucked in, leaving the reserve tank empty.

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The Polo has a plastic impeller on its water pump spindle which can and does break off causing a loss of water flow and overheating. The thermostat has a pin location locating it in housing. These too can break. The fan coming on -as soon as you start up- means the coolant sensor on the engine and the one on the bottom of the radiator are, one or both, are faulty.

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