Cummins Piston Cooling Nozzle (3080708) From Xcec Engine ...A piston cooling nozzle (PCN) is an engine component that sprays engine oil or other fluid onto the underside of a piston, typically in high-power diesel engines, to prevent overheating. It functions by continuously directing a targeted oil jet to the piston skirt and crown, absorbing and carrying away heat to ensure optimal engine performance and prolong component lifespan. The nozzle is mounted on the cylinder block and is activated when sufficient oil pressure is present, unseating a spring-loaded valve to release the cooling fluid.