Coolant

Haven't you forgotten that antifreeze, just like engine oil, has a fixed change interval? Usually it's two years, but you should check your car's service book. The thing is, after a certain time even the highest-quality antifreeze loses its performance properties, can freeze in cold weather, and can damage the car's cooling system. On top of that, during use the coolant gradually gets contaminated, washing out deposits inside the system and mixing with condensate.