Editing Coolant (section)

==Antifreeze==
Over 90% of concentrated coolant is a polyol, a chemical like an alcohol but with multiple hydroxyl groups instead of the one that alcohols have, and is used to raise the boiling point and lower the freezing point when mixed in to water.  Almost all coolants use one or more of three chemicals to provide the antifreeze effect:
*'''Ethylene glycol''': most modern coolants have only ethylene glycol.  It is acutely toxic and sweet, which means it is dangerous for children, pets, and wildlife if spilled in the open, but it is cheap and effective.
*'''Propylene glycol''': started to become popular as a less toxic alternative to ethylene glycol, but now uncommon.  Modern coolants usually use bittering agents to make ethylene glycol unpalatable.
*'''Glycerol''': sometimes mixed with ethylene glycol, it is a less toxic and more environmentally friendly antifreeze.

Pure ethylene glycol has a freezing point of -12C, which is not low enough for reliable use in the UK.  When mixed with water, the freezing point becomes much lower, below -50C at certain concentrations.  Most coolants are formulated to be mixed with approximately 50% water for protection to around -37C.  Propylene glycol has a lower freezing point.  Glycerol is a viscous liquid at room temperature and freeze at 18C, so it must be used in mixtures with other antifreezes and water.

On the whole there is nothing much to worry about.  Coolants all have much the same antifreeze regardless of anything else.  Choose one with glycerol if you really want to be eco, although it will still be mostly ethylene glycol.