Engine coolant, also known as antifreeze, is a liquid that circulates through a vehicle's engine to regulate its temperature and prevent overheating. It is typically made up of a mixture of ethylene glycol or propylene glycol, water, and various additives.

The primary ingredient in most engine coolants is ethylene glycol or propylene glycol, which lowers the freezing point of the coolant and raises its boiling point. These glycols also have good heat transfer properties, allowing them to effectively transfer heat away from the engine.

Other additives in engine coolant include corrosion inhibitors to prevent rust and other forms of corrosion from damaging the engine, as well as lubricants to help prevent wear on engine components. Additionally, some coolants may contain dyes to help distinguish different types of coolants, or bittering agents to make the coolant taste unpleasant and deter pets and children from drinking it.

The specific composition of engine coolant can vary depending on the manufacturer and the intended use, such as for use in high-performance engines or extreme temperature conditions. It's important to use the type of coolant recommended by your vehicle's manufacturer to ensure optimal performance and longevity of your engine.