A liquid cooled internal combustion engine has a cooling system with a coolant liquid flow passage having a drain port and a clog-preventing drain plug having an anti-clog protrusion finger extending through the drain port and into the coolant liquid flow passage when the clog-preventing drain plug is in its closed position. The anti-clog protrusion finger leaves a hole in a clog layer of debris and/or engine combustion products upon removal of the anti-clog protrusion finger from the coolant liquid flow passage upon moving the clog-preventing drain plug to its open position.