After 18 Years....Something New

GeeBee

GeeBee

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Jan 1, 2000
RO Number
385
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2,871
I finally needed my spare raw water pump. I have carried one for 18 years, swapped them out every year, overhauled the core and stored it away on the boat.

Today, on my Mercruiser 7.4 MPI, I spun a impeller. Engine overheated immediately. I was not sure it was the pump, but it seemed likely.

Now you can't change that impeller in the water unless you have a damn good hose pincher, I do, but either way you still have to pull the feed hose off and while you are trying to put in a new impeller, that hose could sink your boat. With an extra pump, pull off the old one, swap the hoses real quick and you are on your way. It is also a real PIA to get to, but I knew that. Have to pull the belt of course, and the fuel filter assembly, then unbolt the pump, swap the hoses then reassemble. Mercruiser, you could have designed it better knowing this is a "dead in the water item."

It all worked out as best as it could. I will never be without a spare pump. You should not be either.

Two interesting things happen. Labor Day on Lake Lanier, busy, busy, busy. I've go my hatch up wrenching on this thing for a hour or so. Getting rocked all over the place. Not once did a single boat stop and do a welfare check, nope, not once. Not that it mattered, I had this pump and a BoatUS card in my wallet as a back up. They just passed by close creating big PIA wakes for me. Geez, I always stop for a "hatch up guy" just to make sure, I guess I am a dinosaur.

Also in typical Lake Lanier fashion, I see as I rise out of the bilge, BoatUS towing a huge house boat. Maybe 75 or 80 feet. He had on his tow lights. Up comes an idiot runabout that starts to cut between the tow! Don't know if the Captain was our fellow RO "Coolbreeze767", but holy crap did that scare me. Idjits, just Idjits.
 
That design was a POS from the get go. Give me a Crusader or a Volvo any time. Fifteen minutes. In your case under your conditions maybe thirty.
 
The open hose flooding your boat problem can be mitigated with the foresight to carry plugs and one small, one large nerf ball. Plugs work just as well on hoses as through-hulls.
 
Why can't you change it in the water? I ve never seen a boat with an inboard and no sea cock.
 
quote:
Originally posted by PascalG

Why can't you change it in the water? I ve never seen a boat with an inboard and no sea cock.

Click to expand...


Chancing the RWC impellor on a Merc could be compared to changing the prop on a bow thruster...blindfolded...while holding your breath....in Pirahna infested waters. Actually the thruster might be easier.
 
quote:
Originally posted by November Charlie

The open hose flooding your boat problem can be mitigated with the foresight to carry plugs and one small, one large nerf ball. Plugs work just as well on hoses as through-hulls.

Click to expand...


You are correct and I had a wood plug standing by just in case.... but really a hose pincher works even better in this case and I had one standing by as well.

Pascal, I/O has a hose from the gimbal to the raw water pump. I wish it had a sea cock and IMHO the design of an I/O should have a sea cock type device on the gimbal inside the transom. However remember it is designed by the same folks who put the raw water pump on the bottom right side of the engine.
 
Dumb design. Is there anyway to put a valve in the hose between the drive and the pump?

It s been 20!years since I ve owned an IO but the pump was at the front with a long hose. Once the hose was unclamped you could just lift it above water line so there was very little water dripping in.
 
Dumb design? You'll get no argument from me.

No, the hose is not long enough nor with the way it is routed could you lift it above the water line. Could you make it longer? I suppose, but you may get into other problems like contact with a hot oil pan etc.
 
My back starts to ache just thinking about pulling that pump off. Fortunately the raw water intake on my bravo 3 is so restricted that it would take a week for enough water to trickle in to sink the boat. Was a constant battle to get enough water through the drive and the narrow hose which makes multiple bends over 90 degrees.

I finally gave up on the horrible factory design, blocked off the intake with a plate, put a pickup on the transom to feed the pump, a drive shower to keep the drive cool, and all is well.
 
People who design such things ought to be made to change all the components before it is allowed

to be sold to the public. I would make it my mission in life to get a valve on that thing some way

some how.
 
They're just like automobiles. They aren't built for servicing - they're built for selling. Servicing is way down on their list and certainly below profits, dealer sales, and bonuses. I too have a Mercruiser, although it's a 5.7. I'm sure the pump is similar and I find it easiest to remove the pump and take it home for bench servicing.
 
6.2 Horizon is no picnic either. 1-2 hours of labor to R&R the pump just to change the impeller.
 
Folks are dumping the OEM pump for a crank mounted pump. Even the purists at Offshore Only are fed up with the design. From what I've read there, the biggest concern was the amount of water required to cool those bigger racing motors and Merc hype about nobody else being able to provide it. Probably not the best thing to say to a go fast guy who's an engineer, with skinned knuckles and money to burn. Most who convert are the DIY crowd. I've yet to find a mech that will do the conversion. Too much money in it for them not to.

I thought the new Merc 4.5 was going to a crank mounted pump. I can't see it on the engine though.
 
Would not the easiest thing is to create a tandem pump, that is piggy backing the raw water pump onto the same shaft as circulation pump? Simply have the aft chamber for circulation and the forward for raw water. You could eliminate a pulley, and put the raw water unit right up front, easy to unbolt a flange and change.
 
Having owned one of those, I have to agree that it is a terrible design. In fact the lack of serviceability on many of today's boats is also terrible. I support the notion that the people who design and build these things ought to be forced to work on them.

Roy
 
quote:
Originally posted by GeeBee

quote:
Originally posted by November Charlie

The open hose flooding your boat problem can be mitigated with the foresight to carry plugs and one small, one large nerf ball. Plugs work just as well on hoses as through-hulls.

Click to expand...


You are correct and I had a wood plug standing by just in case.... but really a hose pincher works even better in this case and I had one standing by as well.

Click to expand...


I wouldn't think use of a pincher would be ideal for a suction hose.

I imagine you could just add an inline full flow bronze ball valve on the suction hose for future ease and safety when dealing with the pump.
 
Not that many places to put that large of a valve, and an inline valve presents strain problems on the hose of its own. Ideally, the valve should be located on the gimbal unit if you are going to pull water in from the drive.
 
So I am rebuilding the old pump yesterday, new impeller and stupid plastic pump body. I go to torque it to spec (very important) 10 to 15 ft-pounds. I place the thing in a spare pump bracket I use to hold it and set the torque wrench for 12.5 ft pounds. Go to torque and I hear "SNAP!". Well it seems I stripped out one of the bolt holes. Turns out the metal side of the pump is aluminum, not steel. So the design of this pump is an aluminum shaft housing and flange, with steel bolts that hold on a plastic pump body that thread through soft aluminum without thread inserts. So I took it over to a machine shop and had them heli coil all 5 bolt holes. Cost me 75 bucks but it is now fixed the way it should be. Next time I rebuild the other one I will do the same treatment. What a POS. YGTBSM Mercruiser.
 
^^^. As much of an improver I think you are, I'm surprised you did not look to convert to crank pumps.
 
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