Well I replaced the water pump in my outboard today. The motor is four years old and was informed that you should replace the water pump every two years. I purchased the entire kit in lieu of just the impeller. I also had to buy special tools to remove the pins that hold the shift linkage so as to drop the lower unit. I could have had this work done for $183.00 but I elected to try it myself. My opinion is that it is not to difficult if you are mechanically inclined. Buy the factory repair manual and follow it exactly. My total cost was only $63 for the pump kit and the tools $84. I figure on replacing the pump (impeller only $24) every two years so I will get more use out of the tools. I always had a nightmare that the water pump would go out miles from the ramp. The impeller that I took out looked good but the manual said that the way it looks does not matter. If you are new as I am to boating and considering servicing your own outboard the water pump is not as intimidating as it might appear. PS the outboard is a Nissan 18HP 4 stroke.