The engine needs oxygen from the air in order for combustion to work. It's imperative that the car's engine is supplied with the correct amount of clean, filtered, cold air. In a combustion engine, the intercooler functions to cool down air once it has been compressed. The overall result of this ensures the engine is working to its optimum, providing more power and fuel efficiency. 

Intercoolers are either front mounted or top mounted in the engine. Front mounted intercoolers tend to work better because they are in prime position to get a continuous stream of air, enabling the intercooler to transfer heat more effectively. Though usually made  of  aluminium, intercoolers are manufactured to be vehicle specific and the material, size and design of the intercooler as well as the location in the engine will vary depending on the make and model of the vehicle. The intercooler is made to be compatible with your car, specifically designed for the make and model of your vehicle.

In supercharged/turbocharged engines in particular, the air is heated to very high temperatures and the intercooler functions to counteract the heat produced by the process of combustion by cooling the air once it has been compressed. Air needs to be as cold as possible before it mixes with the fuel and burns in the cylinders of the engine. The cooler the air, the denser it is, which increases the volume of air being fed into the engine. This leads to a better combustion process in the engine because more of the air/fuel mixture is being burnt in each engine cycle, which improves the overall power, performance and efficiency of the engine. Intercoolers operate with either an air to water system, or an air to air system. The air to water system pumps water through the intercooler and as the compressed air flows through the intercooler, the water being pumped through takes the heat out of the compressed air, cooling it down. The air to air system harnesses air from outside the car to soak up the heat from the air, which cools it after compression. Air drawn in from outside passes through the intercooler, while the hot compressed air from the turbocharger is sent along a network of tubes inside the intercooler which have little fins on the end. These fins act as heat conductors, removing the heat from the air in the tubes and transferring it to the cool air that is  being  pumped through the intercooler, so that the air entering the engine is as cool as possible. The intercooler helps to provide a consistent, constant supply of cold air to the engine, providing the best conditions for optimum combustion.

As with most parts, over time and with continued use the intercooler will lose efficiency. Damage from stones and other road debris adds to the general wear and tear on this part. The intercooler can leak if the metal corrodes which can cause it to lose air pressure. A malfunctioning intercooler will affect the performance of the engine and make it less fuel efficient. Replacing this part with the intercooler will ensure a part that's compatible with the make and model of your vehicle.