Replacing Impeller on seawater pump - 8.1s Mercruiser

mrsrobinson said:
Old thread I know, but I was thinking of doing this one myself versus the mechanic. I am surprised to see the bolts/nuts are metric. I have those wrenches for when I work on my German/Japanese cars, just surprised to see Merc is metric.
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The 8.1 is Merc's metric version of the 496. Just finished doing this myself (again). Always a fun one. I also just replaced the starboard pump with a stainless Hardin (so stainless on both sides now). Make things a little less difficult on yourself and remove the muffler on the port side before you tackle the pump. This isn't really necessary on starboard although removing the port side hose from the riser to the muffler on the starboard engine makes the pump more accessible. Port side get it all out of there.

Good luck!
 
Interesting. I know the various flavors of the 7.4, 5.0 and 5.7s well. This boat (I close later this week) will be my first 8.1s.

I am reading where some say go head and replace the entire housing if you are going to replace the impeller. I get it, for example I replaced the valve cover in my 335i while replacing the valve cover gasket (same amount of labor/time). Is this really necessary for the 8.1s though?
 
mrsrobinson said:
Interesting. I know the various flavors of the 7.4, 5.0 and 5.7s well. This boat (I close later this week) will be my first 8.1s.

I am reading where some say go head and replace the entire housing if you are going to replace the impeller. I get it, for example I replaced the valve cover in my 335i while replacing the valve cover gasket (same amount of labor/time). Is this really necessary for the 8.1s though?
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It all depends on the amount of wear. I think what your friends are suggesting is in relation to how much of a PITA it is to get these pumps out ..so might as well replace. The stock pumps are susceptible to scoring and housings do need replacing every few hundred hours or so is what I've found. I got tired of that (as did my wallet) and so I replaced with the aftermarket stainless. So far in 200 hours of use, I've seen zero scoring in the stainless.
 
I just looked up the stainless ones. $499 a piece including the pulley. Ouch. Money well spent though if one is planning to keep their boat for many years. Doing more research though an OEM looks to be about the same price.
 
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mrsrobinson said:
I just looked up the stainless ones. $499 a piece including the pulley. Ouch. Money well spent though if one is planning to keep their boat for many years. Doing more research though an OEM looks to be about the same price.
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The latest Merc pumps now have replaceable stainless end plates.
 
Hardin Marine if you're interested in stainless.
 
rondds said:
Dennis. That could very well be. I don't know. Maybe someone else will chime in and tell me how much futile labor I went through. Possibly taking off the tensioner pulley but not sure.
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Awesome share! I need to do mine as well according to the hours. Question: If there is still good water flow from the exhaust, is it necessary to inspect?
 
I personally would never trust the amount of water I see flowing out the thru hull. Keep in mind, the water flow you see at the dock is not the same as what you will see at cruise, nor is the load on the engine the same.
 
I have V-Drive 2009 8.1s that replaced the original 7.4s in my 1991 SR 350 SD. Great water flow, temps on guages seem a bit high, at 170 on the stbd and voer 170, maybe 180 on the port. Its seems really hard to get to the pumps due to the V-Drive configuartion. Is this worth paying to have done? I don't mind wrenching and have access to any tools, but I'm also not a mechanic or the size of a leprechan.
 
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