What to Do When the Coolant Warning Light Comes On
If your coolant warning light comes on, it means the level of coolant in your radiator is low and needs topping off.
DO NOT OPEN THE RADIATOR CAP WHEN THE ENGINE IS HOT! This can lead to severe burns! The coolant system is pressurized and it could easily release pressure and spray you with boiling coolant. Wait until the engine is cold.
Top off the system with coolant or with distilled water.
Don’t use tap water – the mineral deposits in it boil out in the cooling system and calcium gets deposited around the inside of the radiator. This will make your system less efficient and will eventually cause it to fail.
It’s always best to use pre-mixed coolant or to mix your own rather than using water. The coolant keeps your engine from freezing and is a corrosion inhibitor to prevent rust. Water can freeze during the winter and can result in gasket failure.