How bad can it be?
Improperly maintained cooling systems can break down any number of ways. Here are three of the most common.
Corrosion: The rate at which a cooling system corrodes often coincides with the number of additives remaining in its coolant. As coolant loses additives, it becomes less capable of removing heat and energy from the engine and reducing the stress put on the metal in the system. Aluminum cooling systems require nitrate-free coolants to best fight off corrosion risks.
Cavitation: Sometimes referred to as liner pitting, cavitation is common when coolant is diluted or low. It occurs when cylinder liners vibrating at an extremely high temperature and rate of speed collide with boiling coolant. Bubbles within the boiling coolant then create small holes in the sides of the liner, which eventually allow coolant to seep into the engine cylinder.
Overheating: One-third of an engine’s energy is displaced into a cooling system during use. As coolant deteriorates it becomes unable to transfer all of this excess heat. This not only increases corrosion and cavitation risks, but also can increase oil temps, particulate deposits within the system and radiator and thermostat breakdowns.