11/10/2021
Engine coolant is mainly drinking water and ethylene glycol or propylene glycol, with many additives, such as for example rust inhibitors, lubricants, and dyes. Alone, drinking water would freeze at 32 °F (0 °C) and boil at 212 °F (100 °C), which makes it unsuitable as an engine coolant. Also under a 16-psi pressure cap, clear water would boil at 252 °F (122 °C), which could be great in warmer climates, but would freeze over night in winter climates.
The addition of glycols extends the liquid temperature selection of water, stopping freezing and boiling at extreme temperatures. The normal 50/50 drinking water/coolant blend drops the freezing indicate -35 °F (-37 °C) and raises the boiling indicate 223 °F (106 °C). A 30/70 mix goes even more, dropping the freezing indicate -67 °F (-55 °C) and increasing the boiling indicate 235 °F (113 °C). Some contact it anti-freeze, but that’s simply a side-impact of engine coolant’s function. Adding pressure further escalates the boiling stage, up to 267 °F (130 °C) for a 50/50 blend.
