In Europe we change the coolant every three years. If you plan on doing the coolant change yourself, do yourself a favour and by yourself a refractometer to measure the exact level of concentration.These refractometers can be bought for as little as AU$25. Do not fall into the trap that more is better, because if you add too much G12 you run the risk of an overheating engine. I set my coolant concentration at -25°C. Naturally you will not need as much, I would set the concentration at about -15°C. As a final note, we also use destilled water to mix with the concetrate, this ensures that there are no minerals in the water.