Impeller

[annascaptain]

I just changed the impeller on my A4. I had cruised with the engine just days before and it worked perfectly -- it took about ten minutes to get to 155 degrees, where it stayed; and always when I started her up, a comforting gush of water would come out the exhaust. But I put in the new impeller and started her up and the temperature started zooming. I checked the exhaust -- there was some trickle, then a bit of a spurt every now and again, like a dying porpoise (apologies to Flipper). The temperature hit 175; it seemd to stabailize a bit, so I thought maybe the new impeller was just stiff, and needed a bit of working in. But there was a trickle of steam -- or perhaps white smoke, but it looked more like steam -- coming out of the exhaust, and only a tiny bit of water, so I immediately shut the engine down. It hit just over 180, and then started cooling, so I am reasonably sure no damage was done to the engine. Still, I can't figure out what it could be -- it ran fine before I put the new impeller in. And I followed the procedure exactly --I put on the new one and the o-ring to secure it, and then a brand new gasket that I carefully seated. I rotated it clockwise as I seated it, and made sure it was as firmly seated as possible. I then tightened the screws as tight as they would go. Any ideas?

[hanleyclifford]

There has been a lot of discussion about new impellers not meeting spec. See some of the the ideas in the cooling section.

[Administrator]

I think Don would argue that it's a worn pump housing not meeting the spec, rather than a brand new impeller.

Bill

[annascaptain]

Thanks -- I might think it was a worn housing, but the old impeller, which you would think would be a looser fit because of its age (I hate to admit it was at least 4 years old -- it was the one already there when I bought the boat). And when I rotated the new one in, it felt pretty darn tight. I realize we are dealing with very exact specs, but still; odd that it would be the housing, if the old one worked just fine.

Could it be that the pump just lost its prime?

[SEMIJim]

Could it be that the pump just lost its prime?

The pump of course "loses its prime" whenever the path between pump and intake is interrupted--such as when the boat's hauled for winter storage (up here in the north) and the system's winterized, such as we do every fall; or when you re-engineer the system to add a strainer, such as I did three seasons ago; or when you remove the pump for a rebuild, such as I did... two seasons ago, if memory serves.

Not a problem.

Possibly a worn cam shoe, as seen on this page.

The pump no longer pumping after the installation of a new impeller is apparently not exceedingly uncommon.

Jim

[hanleyclifford]

Did you actually hold the new and old impellers side by side and compare their thicknesses?

[ILikeRust]

Thanks -- I might think it was a worn housing, but the old impeller, which you would think would be a looser fit because of its age (I hate to admit it was at least 4 years old -- it was the one already there when I bought the boat). And when I rotated the new one in, it felt pretty darn tight. I realize we are dealing with very exact specs, but still; odd that it would be the housing, if the old one worked just fine.

Could it be that the pump just lost its prime?

Just to be clear, the suggestion of a worn housing is getting at wear on the front and rear sides of the housing - i.e., the flat sides of the pump cavity, not the circumference of the pump cavity.

So when you squeeze the new impeller in, it looks exactly right, because the vanes are flexed and pressing firmly against the circumference of the pump cavity. But when you put the cover plate back on, what you don't realize is that there is a tiny bit of clearance between the cover plate and the SIDE of the impeller. Which ruins the ability of the impeller to squeeze water in between its vanes as they get compressed by the shoe. The water can just slosh between the little "compartments" created by the vanes.

[annascaptain]

Thanks, this is all great. I did read all the threads on replacing impellers; and you have cleared up one misconception that I had about the wear -- that it is on the ends, not the circular part of the housing. That explains why Don suggests sanding the face where the backplate sits; and the very faint scoring patterns on the inside of the backplate, almost as though it had been airbrushed. This would also explain why I was getting some water out of the exhaust, but a very abbreviated and erratic amount. After reading all the comments on the previous threads, I had come to the conclusion that I needed a new pump -- but I'll pull the new impeller and compare it to the old one, using my 1/10 mm dial calipers just to be exact. I can use one of my honing stones to polish and true the face of the back plate, and I have some excellent flat metal files I can use to dress the face where it sits. I also installed a brand new gasket; I would hope I can pop the backing plate once and still be able to use it. I would love to just get a new pump, but with a year to go on college tuition, it's worth seeing if this will fix it -- thanks again!!

[sastanley]

annascaptain,

You are on exactly the right track.

As much as I like to support Moyer Marine whenever possible, if you can't re-use the gasket, another forum member has noted that a 1-dollar bill of US currency is the same thickness as a water pump gasket & is made of the just about the best waterproof paper available. When a gasket is $3, and you can cut two gaskets out of a $1 bill, the economics seem obvious.

[ILikeRust]

I would think that if it turns out the new impeller is just a wee bit too "thin" for the existing pump cavity, you probably could reduce the pump cavity by laying a sheet of sandpaper on a flat surface, like a table saw, if you have one, or even a countertop, lay the pump housing down on its face on the sandpaper (with the plate removed, obviously), and rub it back and forth, being careful to keep it flat. Dress it with a stone to get a good, smooth polish and get a good gasket mating surface, and I'd bet it would work.

Of course, I've never had a reason to try, so I'm just making that up, but it might be worth a shot, if you're looking to save some money.

[ndutton]

There are a number of possibilities and often they combine to make troubleshooting an adventure. All four that have been mentioned have been experienced here:

• New impeller shorter than the old one.It doesn't take much, a difference of .005" can prevent the pump from working. We've seen much larger differences than that.
• Cavity wear on the depth. Same comment on 'it doesn't take much.'
• Gasket thickness. Homemade gaskets must be paper thin, not the usual make-a-gasket material at the auto parts boutique specializing in air fresheners. Buy one from Moyer and you can't go wrong.
• Worn cam shoe.

Most guys simply put the old impeller back in until the new pump and extendo bolt arrive from Moyer. I know one guy who sanded down the face flange of his pump to bring the worn cavity depth back to spec with successful results. If considering such a strategy, it's critical the flange is dead nuts flat or you'll be chasing leaks forever.