You should always use distilled water in a cooling system. When you use tap water it will promote corrosion quicker. As for the coolant I've always been in the school of thought that green coolant is green coolant. Things only get different when you get into the reds, pinks, and oranges. I could be wrong about green coolant, but I've never had a problem in a looong time wrenching on cars.Originally posted by streko
Why is it that our subarus require such strict coolant?
Why can't we use tap water mixed with any coolant from the store? Does it have to be Subaru coolant, plus their additive? I think my brother put some tap water with some coolant into my car. What damage will this do? Should I drain it? He just put some to fill up the reservoir