Coolant
Coolant prevents the water in the vehicle's radiator from freezing and boiling and keeps the engine working properly which consists of a mixture of water and antifreeze. Without coolant, the engine would overheat extremely fast, leading to mechanical breakdowns and engine failure. The coolant mixture travels through the engine by a water pump, circulating and absorbing the excess heat which cools the water and sends it to circulate through the system again.
What can go wrong?
Without coolant, the heat that is produced within the engine will cause combustion and essentially destroy it. Water alone will not be able to keep the system cool in hot temperatures, allowing the motor to eventually boil it and freeze in cold temperatures; ultimately leaving the system useless.
What can you do?
Check whether the coolant mixture reaches the "full" line on the side of the coolant reservoir, if it's lower; add a 50/50 mix of water and coolant. Be sure to check the colouring of the coolant and make sure there are no substances floating around or if there are any noticeable leaks whether it's around the radiator or on your driveway. The best step to take in preserving your engine is to get a coolant flush and maintenance check on schedule.