Volkswagen’s small turbocharged engine has a water cooled exhaust. The entire manifold is designed into the cylinder head, allowing for water jackets to surround it and cool the air. In fact, this is becoming a popular design with new, small turbocharged engines from many manufacturers. Why is an integrated exhaust header beneficial?
According to Volkswagen, “Thermal management is key to helping ensure maximum efficiency. The thermostat keeps coolant temperature between 185 and 225 degrees Fahrenheit, influenced by load and engine speed, to achieve the ideal balance between minimal internal friction and temperature management. By directing exhaust gases through the water-cooled exhaust manifold, they are approximately 160 degrees cooler by the time they reach the turbocharger.
Under full load, heat is significantly reduced thanks to the integrated cylinder head and water-cooled exhaust manifold. This new design eliminates the need to enrich the air/fuel mixture under full load, resulting in a reduction in fuel consumption of approximately 20 percent when driving at highway speeds.”