You can use any coolant, as long as its rated for your conditions. I personally use something thats essentially soluible oil. It never gets below zero, so anti-freeze isn't a concern, anti-boil is the only issue, but if it got over 100C i'd have more troubles than boilding coolant, like a cracked head from being too hot.
Just make sure you don't mix coolant types. You will need to purge it ALL before you swap it out. They don't play nice together.
