Any substance, usually a liquid, that is circulated around a vehicle’s engine in order to reduce and regulate temperature by absorbing excess heat and then transferring it to another medium (e.g. the surrounding air) where it is safely and efficiently dissipated. An ideal automotive coolant has high thermal capacity, low viscosity, and is chemically inert and non-toxic; though specific properties can vary widely by intended usage, most ordinary personal vehicles use water as the base coolant with additives such as ethylene glycol or methanol to lower its freezing point, raise its boiling point, and prevent corrosion.