IN THE MAIN ENGINE WITH PISTON COOLING OIL, WE SEE THAT COOLING OIL GOES FROM BOTTOM OF THE PISTON ROD THEN MOVES UP TO PISTON.
THE REASON FOR THE MOVEMENT FROM BOTTOM TO TOP AND NOT FROM TOP TO BOTTOM IS TO KEEP THE CROWN FULL OF COOLING OIL AT ALL TIMES. THIS IS IMPORTANT PARTICULARLY DURING DEAD SPEED WHEN COOLANT IN PISTON IS NOT SHAKEN UP AS WHEN RUNNING AT FULL SPEED.