Distilled water does not have any minerals that can hurt the engine and cause corrosion.

Easiest way I have found is to mix the coolant/water out of the car. If you have an old empty coolant container. Fill it half with water and then fill it up with coolant. 50/50 mix then poor it in. Since you are not going to get all the old stuff out (heater coil and hoses) you will not get the full volume of coolant back in. If you do it out of the car, regardless of how much you put in, it will always be a 50/50 mix.

Hope this helps

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