The second problem facing the boats was the tendency of the cylinders in the diesel engines to overheat. This problem was never rectified and the cylinders would eventually crack after six hours of running at full speed. This was due to early engine design and metallurgical inadequacies. The third and final problem was temperamental emptying of tanks during diving or surfacing. This was rectified by the refitting of faulty valves. After refitting, the ships performed various patrol and training cruises along the west coast.