coolant should cost somewhere around RM 35-40 per bottle of 1.5 litre from any BMW spareparts shop. just add in your expansion tank. buy original BMW coolant, its blue in colour. should be 50:50 ratio between water and coolant. your cooling system filling capacity is approximately 7 litre for 318i and 8.4 litre for 320i-330i. hence, u wont go wrong by adding 2 bottle (3 litre) of coolant