Hi I have a 4.3l mercruiser. where actually is the impeller located and how would you know if it needs to be replaced. Also is this different from the "water pump" thanks 98 Chapparal 200LE
what you are calling the water pump is just a circulating pump. The raw water pump (and it's impeller) are in between the upper and lower sections of your out drive. you must remove the lower unit to change it. Most people myself included consider this a routine annual maintanence item.
check the adults only sticky at the top of this forum and you will find the manual for your drive and it will show you the proper steps to change it.
What outdrive do you have? If it's a Bravo, the raw water pump is engine mounted, Alpha's have them in the drive, unless you have a full closed cooling system, then you could have both.
