The function of the diesel engine piston cooling nozzle is: forced cooling piston, lubrication piston, piston ring, cylinder liner between the friction pair, strengthen the cylinder seal, clean combustion. Engine piston cooling nozzle is usually mounted on the engine main bearing lubricating oil channel, in order to maintain the main oil lubrication pressure engine piston cooling nozzle respectively single ball valve, through the damping hole type. According to the piston cooling nozzle of the body, we must pay attention to the piston cooling nozzle valve opening pressure, damping pressure (about 1.5 kg, not less than 0.5 kg). When the piston cooling nozzle pressure is insufficient, the piston will not be able to get timely cooling. With increasing the temperature of the engine, piston thermal expansion, so that the piston top gap space becomes small, the will and the valve impact, the clearance between the piston and the cylinder becomes small friction intensified, causing cylinder, cylinder sticking accident. Therefore, it is essential to ensure that the piston cooling nozzle oil jet orifice is clear and has a good sealing performance and good injection capability. Engine in the course of normal use, in a "Three Guarantees" period, piston cooling nozzle usually does not appear the fault, but the overhaul cycle of the engine, the piston cooling nozzle must be replaced, in order to ensure the normal operation of the engine. Particularly noteworthy is that in the repair process, maintenance personnel often take plug connected oil crossing, using pump check the piston cooling nozzle is smooth, while ignoring the piston cooling nozzle injection pressure detection. Above is the problem we met in the actual equipment maintenance, similar fault engine Youdao Yici F6L912 air cooled diesel engine, Cummins NT855 water-cooled diesel engine. Attention should be paid to maintenance.