water is the best heat remover - the coolant is there to prevent corrosion and buildup and keep the water pump lubricated.
Too much coolant concentrate actually heats up the engine more than plain water - the ratio should be just right, In Karachi a max of 30% strength is more than enough..
If you are short on buying coolant - just use a/c condensate - A/C dripping water in the radiator - it doesnt carry minerals and salts.