[1PorscheBoxster986]

If your coolant loss is not significant or level is not too low then just top it off with distilled water. If you're going to be pouring a lot of distilled water then you will get bubbles that cause air pockets so make sure you do the proper burping. If you don't know what coolant has been in it then it's time to do a coolant change and flush. Notice all the ifs? It's time to do a coolant change.