I know it sounds alarming, but the truth is not quite how it sounds. PG, propelene Glycol rated at -50 may very well form ice crystals at 20 degrees, but since we are not attempting to operate the cooling system at that temperature, there is no problem with that occurring. Most important to the discussion however, is the fact that water expands(and density changes) when frozen. It is this feature that allows life on the planet, but also cracks our blocks, heads, exhaust, etc. PG and EG(Ethelene Glycol) do not. In fact PG actually contracts when frozen. The most important thing is to get the water out of our beloved watercraft before winter whether by draining or displacing with PG. I kind of do both, but that is another thread that will likely resurface soon due to nature. Hope this calms your fears.