SCAVENGE DRAIN CHOKED :
The engine was MAN B&W. #3 cylinder liner found cracked and same replaced with a spare liner. All systems normalized. Engine was started, found firing on fuel, but the rpm drops back to zero. Checked the fuel system and could not find any fault. M/E tried out from the local stand, same problem existed. Scavenge spaces, under piston spaces inspected, found ok. Air cooler drain checked, found it was choked. On clearing the drain cock, found lot of FW coming out. In this ship, the air cooler was located below the scavenge manifold level. Hence the water leakage due to liner crack, had come accumulated in air cooler, blocking the air supply. Once the drain was cleared and FW taken out, the air passage got clear and the engine started functioning normally.
It is important that he drains of the air cooler has to be clear and should be checked in every watch.