8.1L Raw Water Pump

M

mawyatt

New Member
Dec 13, 2007
1,001
Clearwater, Fl
Boat Info
2008 Sundancer 38DA
Engines
8.1L Mercruisers
How easy is the raw water pump on a (2008) 8.1L to turn by hand? I have pulled the pump and the impeller looks fine, flexable and no sign of any degradation. I can rotate the pump but it does provide some resistance. The impeller was replace less than 50 hrs ago. We ran aground and the raw water flow stopped on the stbd engine. I put a shop vac on the open raw water hoses to pull as much water as I could from the raw water system. There was some sand, but not too bad. I used Hamptons 8.1L impeller change procedure from here years ago on his 340 to get the pump off. His pump and belt are different than on our 2008 38DA 8.1L. Our pump is all brass and has two very small plastic hoses in addition to the much larger inlet and exit raw water hoses. The back of the pump has a type of cylindrical can sitting upright with a small nipple on top with a cut off plastic tube. I have no idea what this is for. The belt does not appear to have a tension adjustment. There is a pulley that the Merc engine manual says provides the belt tension and you use a breaker bar on it to remove the tension and slide off the belt. I'll do an online search to try and find more details but thought I would ask here first. Hey, sorry for the formatting, my work computer won't respond to the return key on this site for some reason, my home Mac does fine!! Thanks for the help, Mike
 
You can turn the pulley by grabbing it with both hands. Not too hard to get it moving, but you definitely will get resistance. The two very small plastic hoses… is one green and the other white? If so, they are part of the air actuated drain system and do not affect the water pump's ability to move water. The cylindrical can is the air actuated drain. The water pump's position is set by the mount and is not adjustable. There should only be one large serpentine belt driving all the pulleys including the raw water pump. There is a tensioner bolt on the opposite side of the engine which adjusts the position of the alternator (I think) to get the right belt tension.

Does it look like this?

http://www.marineengineparts.com/raw-water-pump-496-8-1-l-with-air-fittings.html
 
Jim,

Thanks that's it. I can rotate the pump with only a slight amount of force, so think it's OK.

I don't have an tension adjustment on the alternator. Their is a tensioner on the bracket that partially attaches to the water pump, this is not adjustable. The engine manual states to use a breaker bar on the tensioner to relieve belt tension, then slide belt off the smooth edge pulley. I think Mercury introduced this on later 8.1L models.

Cheers,
 
Hey mike I have an '06 496 mag in my boat I have a spring loaded tensioner as does my buddy with an '09 engine. My engine developed a problem with not enough suction. I took pump apart and found the impeller was ok but there was a groove cut into the brass. I found a place in Louisiana that had a retro fit kit with ss wear plates on either end of the impeller, aftermarket marine, is the name ot the place. About $90 for the kit, works great. I would just watch your temp gauges for now, though. Good luck.
 
Thanks guys. I didn't see any wear or grooves in the main brass casting, but some were in the brass cover plate. Is this where you saw the groove?

Regards,
 
Wear is an issue on the Merc 8.1 pumps and some of its brothers and sisters. The Hardin pump is Stainless Steel and has a wear plate that can be replaced. If you wear out the inside of the Merc pump, you have to junk it an buy a new one. The Hardin pump only requires a rebuild kit that is <$100.
 
Ya the grooves were in the aft section of the pump. The kit I was talking about is for our brass pumps. My buddy had the same problem with his brass pump so I rebuilt it for him. They also have a complete rebuild kit for a little more money.
 
Got the pump out (wasn't too bad) and disassembled it. The impeller looked fine and the pump housing looked OK with no signs of scoring, the end plate that covers the top of the impeller has some scoring though. Put the pump back in (much more of a pain!!) and ran the engine yesterday, the water pressure is lower on this engine but the engine temp is fine. Took the boat for a ride and everything was Ok (except for vibration probably due to prop from running aground which started this whole episode for me!), engine temp matched the other engine at all RPMs, water pressure just lower. I'll watch the engine temp and water pressure closely and plan on trying the rebuild kit end plate…thanks.

Now on to the Kohler generator impeller replacement. The generator is running hotter than normal under load, so I suspect the impeller needs replacing…that should be much easier!!!
 
mawyatt said:
Now on to the Kohler generator impeller replacement. The generator is running hotter than normal under load, so I suspect the impeller needs replacing…that should be much easier!!!
Click to expand...

An easy 5 minute job. I recommend you chage that impeller annually...
 
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