Abstract: The present invention relates to a system for confirming the position of an oil jet in diesel engines. The system includes a mounting means with a hole formed at the bottom end for receiving the nozzle end portion of the oil jet. At the top end of the mounting means is a light emitting element positioned in front of the center of the nozzle end of the oil jet. The light emitting element is connected to a power supply. A light projecting means is inserted in the mounting means in front of the light emitting element. The light projecting means projects the collected light from the light emitting element in a straight line. A light receiving element is mounted in an oil hole of a piston, and receives the light projected from the light projecting means. The light receiving element actuates an alert means when it detects light from the light projecting means to allow confirmation of proper oil jet alignment, thereby improving the piston lubrication and engine cooling.