Mercruiser Raw Water Pumps

[mobocracy]

I've been reading up on the process for impeller changes on Mercruiser engines. I am not an engineer or experienced with these things but it seems like a really dumb design.

If they're going to use a fast-wearing material for the impeller, why make replacing it involve so much disassembly? It looks to me like from posts here, youtube videos, etc, replacing it in the boat involves pulling out the entire pump assembly. Couldn't there have been a design with an easily accessible pump housing cover?

Better yet, why make the impeller out of rubber at all? Why not make it out of metal? Of course this might imply a more complex straining system if part of the purpose of the rubber impeller is to provide give if junk is ingested into the intake.

Which itself systems to be a system design problem -- how about some kind of intake filtering that prevents ingesting sand or other debris? I'd rather check and clean a sea strainer once a week than tear out the pump to replace the impeller, even if the filtering was necessarily limited to maintain water flow volume I'd rather replace an entire all-metal pump every 5-7 years vs. hours of labor ever 1-2 for a self-destroying impellers.

There seem to be other problems besides the impeller, the OEM pump impeller wears against the housing. It looks like a company called Hardin marine makes a replacement pump that fixes this, using replaceable wear plates that keep the impeller from destroying the housing. I just recently bought a 2007 310DA with 350 Mags and was having the impellers replaced as PM and of course got the call that one of the pump housings fell apart as it was being removed and needed to be replaced.

The Hardin pump actually looks like a significant upgrade over the factory pump. I have bookmarked that site so that I might even proactively replace both sea water pumps when its time to service the impellers.

OK, I'm sure I don't know what I'm talking about here and there are reasons for these designs that go beyond "it was the simplest way to make a GM block into a marine engine" and "mercury market dominance means we don't have to try harder".

 

[Ididntdoit]

look at crank mounted pumps.......far more accessable for service......also a seacock and strainer is an easy upgrade...

 

[mobocracy]

look at crank mounted pumps.......far more accessable for service......also a seacock and strainer is an easy upgrade...

Have you actually done this and how much work was involved? I don't get many hits in Google for this as an obvious replacement strategy for the existing pump. The closest match I found was the Sherwood 105 but nothing about how it would get installed on the Mercruiser, and some people who say that pump doesn't last, either.

While it makes impeller replacement easier, I'm still curious what the design/engineering rationale on the pump itself is to use what amounts to an easily degraded impeller.

I'm not so unreasonable to not recognize that all moving parts will wear eventually, but a design that is durable to a few hundred hours vs. much less with a rubber impeller seems to make much more sense.

 

[CaptRonn]

Have you actually done this and how much work was involved? I don't get many hits in Google for this as an obvious replacement strategy for the existing pump. The closest match I found was the Sherwood 105 but nothing about how it would get installed on the Mercruiser, and some people who say that pump doesn't last, either.

While it makes impeller replacement easier, I'm still curious what the design/engineering rationale on the pump itself is to use what amounts to an easily degraded impeller.

I'm not so unreasonable to not recognize that all moving parts will wear eventually, but a design that is durable to a few hundred hours vs. much less with a rubber impeller seems to make much more sense.

There is no problem with the rubber impeller currently in use. Changing them is a relatively simple task using basic hand tools. As far as life of the impeller on a pleasure boat, simply change them once a year and that usually results in no problems. I have seen them go much longer than that btw.

The enemy of the rubber impeller is non use. Let one sit for prolong periods and it will take a set, as well as start to deteriorate. Ones that get constant use tend to last longer.

 

[CliffA]

I've been reading up on the process for impeller changes on Mercruiser engines. I am not an engineer or experienced with these things but it seems like a really dumb design.

If they're going to use a fast-wearing material for the impeller, why make replacing it involve so much disassembly? It looks to me like from posts here, youtube videos, etc, replacing it in the boat involves pulling out the entire pump assembly. Couldn't there have been a design with an easily accessible pump housing cover?

Better yet, why make the impeller out of rubber at all? Why not make it out of metal? Of course this might imply a more complex straining system if part of the purpose of the rubber impeller is to provide give if junk is ingested into the intake.

Which itself systems to be a system design problem -- how about some kind of intake filtering that prevents ingesting sand or other debris? I'd rather check and clean a sea strainer once a week than tear out the pump to replace the impeller, even if the filtering was necessarily limited to maintain water flow volume I'd rather replace an entire all-metal pump every 5-7 years vs. hours of labor ever 1-2 for a self-destroying impellers.

There seem to be other problems besides the impeller, the OEM pump impeller wears against the housing. It looks like a company called Hardin marine makes a replacement pump that fixes this, using replaceable wear plates that keep the impeller from destroying the housing. I just recently bought a 2007 310DA with 350 Mags and was having the impellers replaced as PM and of course got the call that one of the pump housings fell apart as it was being removed and needed to be replaced.

The Hardin pump actually looks like a significant upgrade over the factory pump. I have bookmarked that site so that I might even proactively replace both sea water pumps when its time to service the impellers.

OK, I'm sure I don't know what I'm talking about here and there are reasons for these designs that go beyond "it was the simplest way to make a GM block into a marine engine" and "mercury market dominance means we don't have to try harder".

just be thankful you don't have V drives......:smt013.......with BIII drives at least you have access to the pumps.....

cliff

 

[Boater420]

deleted

 

[Stee6043]

just be thankful you don't have V drives......:smt013.......with BIII drives at least you have access to the pumps.....

cliff

This is no fricken joke. $800 later and fresh coolant in both motors.......

 

[CliffA]

This is no fricken joke. $800 later and fresh coolant in both motors.......

I've replaced the impellers on my boat once......I will think long and hard about doing it again.......this is one of those jobs where 'writing a check' is an attractive alternative......

cliff

 

[scoflaw]

There is no problem with the rubber impeller currently in use. Changing them is a relatively simple task using basic hand tools. As far as life of the impeller on a pleasure boat, simply change them once a year and that usually results in no problems. I have seen them go much longer than that btw.

The enemy of the rubber impeller is non use. Let one sit for prolong periods and it will take a set, as well as start to deteriorate. Ones that get constant use tend to last longer.

Me thinks the captain has not had the pleasure of changing these impellers out. Basic hand tools yes, relatively simple task.... no freakin way.

 

[mobocracy]

Me thinks the captain has not had the pleasure of changing these impellers out. Basic hand tools yes, relatively simple task.... no freakin way.

I think this is the crux of the design. I guess I'm willing to accept that the rubber impeller is an unavoidable design choice based on a lot of constraints, but the real killer is that the pump itself isn't designed with any kind of ease of changing.

I haven't actually tried it, but removing the pump assembly appears to be necessary to gain access to the housing face where the impeller is actually located. I watched two videos, looked at some threads here, and my summary is that the task isn't exotic but is time consuming and troublesome.

If the impeller is a rapid wear item, then the pump design should reflect that and make the impeller easy to change.

 

[bbwhitejr]

There is a very good thread on here about changing out the impeller on a 350 Mag. I believe it was written by Dave S. on the 260DA thread. Some videos and instructions will indicate changing out the impeller without removing the pump, but everyone who has done the job highly recommends removing the pump and changing the impeller on the work bench.

I boat in very clean fresh water and am about to start the 5th summer on my impeller.

Bennett

 

[northshore]

If the impeller is a rapid wear item, then the pump design should reflect that and make the impeller easy to change.

Not when bean counters run the world.

"You want to add how much to the design cost!?"

 

[CaptRonn]

Me thinks the captain has not had the pleasure of changing these impellers out. Basic hand tools yes, relatively simple task.... no freakin way.

Me thinks that I have changed out a lot of impellers on ALL of the various boats I've owned, since I am the one that does the maintenance.

 

[CaptRonn]

I think this is the crux of the design. I guess I'm willing to accept that the rubber impeller is an unavoidable design choice based on a lot of constraints, but the real killer is that the pump itself isn't designed with any kind of ease of changing.

I haven't actually tried it, but removing the pump assembly appears to be necessary to gain access to the housing face where the impeller is actually located. I watched two videos, looked at some threads here, and my summary is that the task isn't exotic but is time consuming and troublesome.

If the impeller is a rapid wear item, then the pump design should reflect that and make the impeller easy to change.

Part of my background is airplane and helicopter maintenance, so I'm no stranger to turning wrenches.

While some boat manufactures don't build their boats to be maintained (Sea Ray is equally guilty on some models),one of the items I look at before purchasing a boat is how well it can be maintained by me.

Again, I just don't see changing impellers as such a horrible job. YMMV

 

[Lazy Daze]

I think the reason for the rubber is because it IS in a high wear place. If we placed a finer filter (to filter sand) in front of the impeller, I would imagine that it would also restrict water flow to the engine. So if a metal impeller was used, it may very well wear out just as fast as the rubber one, but yield a much higher replacement cost.

You could definitely re-think the system and install a crank-mounted pump. I haven't done one myself, but it's not hard to understand how or what needs to be done. It's not a small project - it's not terribly hard, but it does require some thought and new parts. The main things being the intake hose needs to be extended/re-routed, along with the output hose. Probably a couple other odds-n-ends that I'm not thinking of right now. I thought about doing it to my last boat - but in the end, it takes me less than an hour start-to-finish to do it the way it is and I just couldn't justify it.

I also understand (from plenty of first-hand experiences!) the "hassle" that this job can be. Once you do it a few times, though, it's not that bad since you can start to do things by "feel" without actually seeing it. And, certainly, the particular engine room space has a lot to do with it. On an "easy to get to engine" it's maybe a 45 minute to hour job (once you're comfortable with it). Maybe another half hour for those that are harder to get to.

Take the pump AND bracket off as one piece. Getting to the (3) bracket bolts is pretty easy. The struggle is with the two big hoses. But the use of the right tool extensions (and working by feel) and a hose removal tool helps tremendously. It also helps to have two elbows...

 

[CliffA]

It also helps to have two elbows...

and 6ft long arms........:wink:.......

cliff

 

[northern]

Buy a complete spare and just exchange the pumps one at a time. Take one out put the new one in open a beer rebuild the one you took out. Next day change out the other one and rebuild it. Nothing worse than having one fail when you are out and having fun. Once I went 40 miles with a failed pump.

 

[scoflaw]

Me thinks that I have changed out a lot of impellers on ALL of the various boats I've owned, since I am the one that does the maintenance.

I'll call you out on that statement. Airplanes and helicopters don't mean diddly Changing out the OP's impellers with that boats configuration is def. not a simple task.

I have several words to describe the R/R procedure and SIMPLE isn't one of them

 

[CaptRonn]

I'll call you out on that statement. Airplanes and helicopters don't mean diddly Changing out the OP's impellers with that boats configuration is def. not a simple task.

I have several words to describe the R/R procedure and SIMPLE isn't one of them

Whatever. I do my own maintenance and know how to use tools (hence why I mentioned my background in maintenance). As someone else posted it's not that difficult after you've done it a few times, and I've done it many many times.

But I do realize there are some (perhaps you included) that are clueless when it comes to maintenance and a job like this seems OVERWHELMING.

 

[scoflaw]

Whatever. I do my own maintenance and know how to use tools (hence why I mentioned my background in maintenance). As someone else posted it's not that difficult after you've done it a few times, and I've done it many many times.

But I do realize there are some (perhaps you included) that are clueless when it comes to maintenance and a job like this seems OVERWHELMING.

i'm 65 , and wrenching and maintenance is what I do and have always done, and no stranger to this pump. Maybe the the captain can give his age, weight and height, that might give a clue to how this job is termed SIMPLE