Very often the cause of coolant being expelled from the reservoir is due to a faulty head gasket leaking compression air into the water jackets. When the engine stops circulating the coolant, with the water pump, the bubbles collect together in the radiator as they rise to the top. Then the hot compressed air passes through the pressure relief valve (often radiator cap) and enters the reservoir, thereby blowing coolant out of the overflow tube.
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Very often the cause of coolant being expelled from the reservoir is due to a faulty head gasket leaking compression air into the water jackets. When the engine stops circulating the coolant, with the water pump, the bubbles collect together in the radiator as they rise to the top. Then the hot compressed air passes through the pressure relief valve (often radiator cap) and enters the reservoir, thereby blowing coolant out of the overflow tube.