Antifreeze is used to protect the engine coolant from freezing. In areas of the world where the temperature drops below 32 degrees F (0 degrees C), at least a 50 percent glycol concentration (antifreeze) is needed to avoid cracked blocks. Antifreeze also raises the boiling point of water. As such, a minimum of 30 percent glycol concentration is recommended in warm climates for protection against engine overheating.
All modern diesel engines also require rust inhibitors. Otherwise, the cooling system will rust and lose efficiency and the engine will overheat. In addition, minute holes can form on the cooling water side of the cylinder liner, which will eventually cause water to leak into the combustion chamber and ultimately destroy the engine.
Some brands of antifreeze contain rust inhibitors, although rust inhibitors can also be purchased separately. Be aware that as antifreeze ages, it may still protect coolant from freezing or boiling but the rust inhibitor chemicals may deteriorate. A simple litmus paper test is available to check the proper strength of the rust inhibitors. As a rule of thumb, check your cooling system fluids after every 250 hours of operation.