I'm looking to change the lower unit water/pump on my 1999 Mercury 115 horse, 2 stroke, 4 cylinder.

I've watched videos and the process seems pretty straight forward. You take off the lower unit, take off the old pump, put the new impeller in the new housing (water pump) and mount it, then put the lower unit back on and done.

I was told to make sure you mark the lower unit rod with a removable marking so it will line back up when you remount the lower unit. I was also told to make sure you seat the impeller the correct way so that it will spin in the housing in the right direction by looking at the old one.

It seems to be about a 15-20 minute process if you know what you're doing.

Anyone else have any tips or hints on how to change the lower unit water pump/impeller?

Dream on Alice, your in Wonderland if you think you will do it in 15-20 minutes. On most motors it will take that long or longer just to disconnect the shifter. Let me just say, being your first, Don't have anything planned for a couple of hours when you start.

I would recommend getting a manual and an extra body to help, especially this being your first one. That LU is heavy, trying to get it in place and hold it there to start the bolts can be a challenge. I always rub a little Lubriplate 105 inside the housing when putting it back together. Make sure all the blades are pointing in the right direction.

Dream on Alice, your in Wonderland if you think you will do it in 15-20 minutes. On most motors it will take that long or longer just to disconnect the shifter. Let me just say, being your first, Don't have anything planned for a couple of hours when you start.

I would recommend getting a manual and an extra body to help, especially this being your first one. That LU is heavy, trying to get it in place and hold it there to start the bolts can be a challenge. I always rub a little Lubriplate 105 inside the housing when putting it back together. Make sure all the blades are pointing in the right direction.

 

 

 

Thanks. It's looking like it takes longer than I thought. lol.

 

 

 

 

Some others have said that the motor needs to be in forward or reverse, some saying it has to be specifically in reverse.

 

 

Is that correct?

That's what manuals are for. It's been a long time since I've had a merc, but it seems like my 115 said to put it in reverse, but like I said, it has been too long to put any faith in this old memory. It's not going to damage it, it's just the way the position the shift rod has to be in to make putting it back in a lot easier.

BE SURE you put grease on the drive shaft splines. I've seen drive shafts rusted in the crank that would not come out. I know a guy that had to destroy his LU so he could cut the driveshaft. Then pull the power head off and use heat to get it out of the crank

That's what manuals are for. It's been a long time since I've had a merc, but it seems like my 115 said to put it in reverse, but like I said, it has been too long to put any faith in this old memory. It's not going to damage it, it's just the way the position the shift rod has to be in to make putting it back in a lot easier.

BE SURE you put grease on the drive shaft splines. I've seen drive shafts rusted in the crank that would not come out. I know a guy that had to destroy his LU so he could cut the driveshaft. Then pull the power head off and use heat to get it out of the crank

I just read one where it said it had to be on gear and then another that said it doesn't but putting it in reverse makes it easier. lol. Contradictions.

I'll use grease for sure.

I changed mine in a older boat and it wasn't rocket science and kind of like you think about dropping and getting to pump. The pump is actually just a rubber piece. When you get to taking the old one out just make sure no pieces were shot up the intake so its not clogged by a broken piece. You can do it yourself and don't need to pay high mechanic bill to have it fixed.

I used a car jack with a couple of old shirts paddling the jack keel and it helped raise and lower when trying to take the bolts on and off.