When the word coolant is used in can mean a couple of things. Coolant made up of antifreeze and water out of your household tap, 50-50 solution, would last for around 3 years. Coolant made up of antifreeze and distilled (de-ionised) water, 50-50 solution, should last for around 5 years. Because of the nonsense surrounding 'coolants' always adhere to the instructions on the supply container. If you live in an area of the world subjected to very low temperatures you could look at a coolant change on the outset of winter as a sort of insurance. An antifreeze mixture should only be at a max of 50% as any greater amount of antifreeze will increase the freezing temperature. ie 50% antifreez would be -30C freezing, 60% antifreeze would be -20c.