[geozukigti]

carbon buildup inside your engine can also cause pre-detonation. Pre-detonation can, and will cause some hot-spots in your engine, causing even a 100% glycol mix to boil instantly. Once you get a vapor pocket, the pressure in your cooling system will go through the roof, and blow off enough coolant to fill the overflow tank. Try running a couple tanks of 94 octane through it, clean things up a bit.