Don’t drive the car.

Let it cool down, mix 50/50 BMW coolant and distilled water. Open the reservoir and turn the car on with the heat on full blast. It may take a while for the engine to warm up and the thermostat to open for it to suck any coolant out of the reservoir (if any). Continue adding mixed coolant to the full mark. Check it again after driving it a day or so.

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2007 E70 4.8i