The ratio of water and coolant mentioned in Manual is important. I had found twice that service people were using water for toping up coolant. This can be done only on emergency. The temperature absorbing capacity of water and coolant liquids are different. So by diluting with water than the prescribed ration will end up changing the working temperature of engines. Also I read from forums that coolant liquid is rust inhibitor and diluting it will cause premature coolant pump failure(Experts can explain it more). Also tap water should not be used since the minerals in it will crystallize inside the radiator and can plug the radiator. I have the following doubts. 1.Do we have to use hot water for mixing coolant? 2.Does all Fiat use same type of coolant from their launch? This is important since one should not mix different coolants. 3. When I compare my alto with Fiat I found the coolant chamber has more air bubbles. Is it common with all users?