So i have the right coolant (Zerox G-05) and distilled water ready to add to my system since I have a very slight leak from the radiator. Manual tells me to check the level when its running and warm, but never specifies when I can open the bottle to add more safely. Dont want to learn this the hard way so, when are you supposed to add the coolant mixture so that you can measure it right and not overfill? When warm and running, or cold? Thanks in advance.