Before you can understand how an exhaust gas recirculation (EGR) cooler helps, you have to know what the EGR valve does. When the EGR system senses back pressure from the exhaust, it channels exhaust gas back into the engine — more specifically, the combustion chamber. This provides several benefits, including better fuel mileage and allowing the engine to warm up faster since the air in the combustion chamber is warmer. At the same time, the recirculated exhaust is cooler than the combustion chamber, so it also cools the engine while increasing the temperature of the gas.
Furthermore, exhaust is used in hybrid vehicles. When the vehicle comes to a stop, the combustion engine shuts off. If the engine is off too long, it gets cold. The exhaust gas keeps the combustion engine from cooling too quickly, thus keeping it more efficient when the hybrid switches from electric to fuel.
When the engine is too hot, the EGR system diverts the exhaust gas elsewhere so the engine doesn’t overheat. Because introducing exhaust gas into the combustion chamber is excellent for the environment in that it reduces the amount of nitrous oxides emitted into the atmosphere, if an engine uses an EGR cooler, more of the exhaust gas can be diverted into the combustion chamber.
Nitrous oxides are created with high temperatures. A vehicle can register exhaust manifold temperatures of 600 degrees Fahrenheit and more. By cooling down the engine with the exhaust gas, the engine puts out less nitrous oxides, which is much better for the atmosphere.
Another benefit of using an EGR system set up with a cooler is that the fuel burns cooler, which means that there is less detonation. Thus, the timing on the engine can be changed to further increase fuel mileage. It also helps keep heat transfer energy loss lower, which means more of the horsepower and torque created by the engine is transferred to the wheels.
By using an EGR cooler, you still get the benefit of warming up the fuel and coolant and cooling off the engine, but because the exhaust gas is cooler than without using an EGR cooler, the engine uses more of the recirculated exhaust in the engine, thus reducing the nitrous oxides emitted into the atmosphere.