Impeller replaced, but did I screw up? - SailNet Community

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  #1  
Old 02-24-2010
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Impeller replaced, but did I screw up?

A normal person with even a smidgen of mechanical aptitude wouldn't ask this question, but, well...that's not me.

I recently bought an '86 Hunter 28.5 and, after reading here about the importance of periodically changing the raw water pump impeller, I decided to ask the previous owner, who had owned the boat since new, when he had last replaced the impeller. What's an impeller? he asked. The impeller in the pump was the one that came with the boat from the factory in 1986! So I ordered the part from Yanmar and, after being assured by members here that it was an easy job, decided to install the sucker today. When I opened the pump up, I was shocked to see that only two of the six impeller vanes were still there, but they apparently had been moving enough water to prevent serious overheating. Using the Yanmar manual, I carefully removed the old impeller, put in the new one, got the vanes all headed in the right direction, cleaned off the old gasket material, applied some sealant to the new gasket, put the thing back together, opened the seacock, and cranked her up. Can't tell you how proud I was to see a cloud of pink in the water behind the boat (you can't see the cooling water discharge from topside on the 28.5, so the antifreeze being discharged told me the pump was at least moving water through the engine). Proud again when I checked the pump and found no leaks. To make this long story shorter, I apparently was so anxious about getting the old impeller out, the new one in, and the pump re-sealed that I overlooked one of the steps -- putting some grease on the impeller sides and blade tips. Didn't even think about it until several hours later and a hundred miles away from the boat. Is that a big oversight or a little oversight? Would someone please tell me it's a little one since I won't get back to the boat for a few days and the gasket sealant will be fully cured by then, which would necessitate my ordering a new gasket and going through the whole process again. Also, is there an easy way to determine if any of the missing four vanes are stuck in the discharge line? Should I shoot some compressed air in the line to make sure it's clear?

Sorry for length of the post, but I am truly half brain-dead when it comes to mechanical things and I tend to worry about things until they're resolved. Any help on this subject would be greatly appreciated. Thanks.
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Old 02-24-2010
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the grease probably wont be a big deal, if everything was wet before, its just for start up lube.

as for the old vanes, you might want to pull the water lines and check them, they most likely got stuck at the line to block hose barbs. this is a good time to check all the hoses and clamps too.
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Old 02-24-2010
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Country, I don't think there should be antifreeze coming out of the discharge.
If I am missing something....someone please educate me.

I am totally amazed an impeller could make it that long...that’s one bad boy little impeller.

I wonder what else the PO did not check???
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Old 02-24-2010
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Quote:
Originally Posted by steveg353 View Post
Country, I don't think there should be antifreeze coming out of the discharge.
If I am missing something....someone please educate me.

I am totally amazed an impeller could make it that long...thatís one bad boy little impeller.

I wonder what else the PO did not check???
He probably has raw water cooling and had the engine full of antifreeze which was pumped out (let's hope it stays above zero).
I would'n t worry about the grease; impellers are water lubricated. About those pieces in your engine...Difficult to answer that one. They may have left the engine or they may block some of the cooling passages.
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Old 02-24-2010
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I just gave myself a big "duh" Thats something I haven't had to think about down here on the gulf coast....although, it snowed just a tiny bit today but never got below 36.
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Old 02-24-2010
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Me too!

Had a similar problem w an older boat and when I opened the cover found zero blades on the core. I used bent wire w hooks on the end to dig and fish out the missing blades. Hopefully you got them all.
On our newer 'old' boat I replaced the impeller and then two years later was enroute to a weeklong sailing vacation.... and noticed no water coming out of the exhaust. I shut down and checked the impeller. Half the blades were gone. It took about half an hour to replace and get under way but I will definetely replace it yearly now. And I always have a spare on board!
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Steve, my engine has an open-end hose that can be inserted into a jug of antifreeze and, with the seacock closed, the antifreeze is pumped into the raw water system (the engine has to be shut down at the right time or the antifreeze will be pumped completely through the engine.As for the vanes, it appears to me from looking at the raw water diagram in the Yanmar manual that the pump is on the discharge side of the system, meaning that it "sucks" water through the engine. Someone please correct me if I'm wrong, but if that's the case wouldn't the vanes go into the discharge line rather than the engine?
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Took another look at the diagram and I am obviously wrong about how the raw water system works. I'll check the lines at the first opportunity and hopefully will find the missing vanes.
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Old 02-24-2010
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Quote:
Originally Posted by countrygent5201 View Post
Took another look at the diagram and I am obviously wrong about how the raw water system works. I'll check the lines at the first opportunity and hopefully will find the missing vanes.
Yeah, it pushes the water through, not pulls it.

Back to your original questions:

There's no issue with the impeller and the lack of grease. The boat is just sitting there with the engine off. In fact, I don't even put grease on the impeller blades and have never had an issue (I do occasionally run just a very thin amount of grease around the inside of the impeller chamber, but not every time).

As for the old impeller blades... A bit of a quandary there. They could have broken off intact, or given how old it was they might have even slowly disintegrated in small bits. I don't think anyone can tell you for sure because I don't think anyone has run an impeller that long! (Actually, I'm skeptical that it was NEVER replaced. Maybe a mechanic took care of it and the previous owner wasn't savvy enough to follow along).

But you haven't said whether your engine is raw water or fresh water cooled (someone else did, but I'm not sure how they reached that conclusion). A "raw water cooled" engine does not have a heat exchanger with anti-freeze reserve. Instead it just pulls raw water from outside the boat and pushes it through the cooling veins of the engine. A "fresh water cooled" boat has a heat exchanger with antifreeze reserve, and simply uses the raw water to cool the heat exchanger.

So the path you have to follow is different depending on what kind of cooling system you have.

For those from the "south" wondering why he'd be discharging anti-freeze, either system is winterized against freezing damage by running non-toxic antifreeze through the "raw water" portion of the cooling system. This gets mixed with and discharged out the exhaust tube.
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Old 02-24-2010
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The lack of grease shouldn't be an issue as long as you've got water flowing into the system. The missing blades are likely stuck in the heat exchanger, and if you haven't taken that apart and cleaned it out, it is probably past due for it. It'll probably have bits of old zincs too. Speaking of zincs, have you replaced the zincs in the engine?
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