Pull out old impeller with an impeller puller, saves a lot of cussing. Take the old one out coat in Vaseline/silicon spray insert it into a ziploc bag and put it in your glove box with a new seal in case you have a failure on the water. Take the one that was in the glove box and put it on a shelf to show how many you have changed. I will never understand why you would try to save $40 on an impeller that is the heart of a cooling system on a boat that you will expect to run perfectly all summer. I guarantee most of us spend more than that on the first Beer run of the summer. Put a new one in EVERY year and pinch pennies somewhere else.