6.6 LITER DIESEL. Center. OIL & COOLANT PIPES. Return hose. A Line that carries Coolant from the engine through the Turbocharger and back into the engine. Hoses carries permanent Coolant, or antifreeze, throughout the engine, heater, and radiator. Line used to transmit oil amongst the turbo, interCooler and engine. Oil. pipe. Center. Engine.