okay, now everyone has me worried, because my bus is a new purchase and I have no idea what is in it right now. Maybe I can go back to the old owner and find out, if not, what is the safe way to top off the antifreeze without changing all the fluid out. On that thought. How long is the antifreeze good for. My bus really didnt see a lot of action before I bought it because the owner had upgraded and just didn't want to get rid of the old bird. I did have a mechanic go over the bus, but no mention of the antifreeze... Should I test the antifreeze other than a simple ph test, or just be safe and flush the system. The bus probably has had 45,000 miles put on it over the last 10 years. And most of those miles were in the first 5-6 years. The last 2-3 years have been very, very mild.