Check the impeller regularly and have a spare. Impellers are the heart of an engine s cooling system and require regular inspection and replacement under normal operating conditions. Running through silty or sandy water or running a pump dry can ruin an impeller quickly and cause the engine to overheat. It is important to monitor cooling water outflow and replace the impeller at the first signs of reduced outflow. Sierra replacement impellers are engineered to meet or exceed Yamaha and Mercury specifications to give boaters and technicians the confidence of an OEM fit and function. These neoprene impellers are compatible with many 4hp 6hp Mercury and Yamaha outboards. Because unexpected failures can happen, it is important to have a spare impeller onboard to save the day. Use our Engine Parts Selector or call 1-800-BOATING with your outboards serial number to confirm this is the correct impeller for your engine.