Engine coolant protects against overheating, freezing and internal corrosion, and is available here as concentrate and as ready-mixed premix.

Coolant is glycol, water and an inhibitor package. The glycol raises the boiling point and lowers the freezing point, but it is the inhibitor package that does the long-term work of protecting aluminium heads, cast iron blocks, brass radiators and solder joints. Different technologies exist, and mixing them can drop inhibitors out of solution as gel or sludge, so a full flush is the safe route when changing type.

Never run an engine on water alone. Even in a warm climate, water without inhibitor corrodes the cooling system and forms scale that reduces heat transfer. Check coolant condition and level at every service, and only ever open a hot system once it has cooled.