I am driving a 2004 e60 with 70k Milage. Needs to top-up coolant reservoir every 2-3 weeks with about 300ml of water. Is it normal . Btw I top it up with tap water only. , will it damage the car . Thinking going to petrol kiosk to buy coolant for future top up , what spec of coolant is for E60 ? Anyone out there can advise ? Thks