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#1
IP: 73.163.155.191
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How can a simple impeller pump fail completely?
Today was when I started my trusted A-4 the first time in the season. She started right away, without ether or other tricks, though it took maybe 15 or 20 seconds until ignition. Not surprising given that I squirted oil in the cyclinders because her long winter nap.
However, the sound was wrong. After some trouble shooting, I discovered that the raw water pump does not pump. At. all. I took off the outlet hose, right at the pump and no water coming out of it when the motor is turning. Actually, for about one second some water gushed out, then nothing anymore. Opened it up: shaft is turning, impeller is turning, impeller is intact (metal center not separated from the rubber vanes -- I have had that happen before), strainer is open (seacock too ) and water-filled. What could have gone wrong? This is such a simple thing, just an impeller turning in a cavity. I winterized the motor last December by sucking in antifreeze from a bucket through this very pump, with no problem at all. FWIW this is an Oberdorfer 201 pump, which came with the Indigo freshwater cooling system. Any ideas? Thank you! |
#2
IP: 69.250.111.245
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Sometimes, I have found you need to re-prime the pump given all the things you are reporting. Can you pour fluid into the pump inlet with a funnel???
__________________
-Shawn "Holiday" - '89 Alura 35 #109 "Twice Around" - '77 C-30, #511 with original A-4 & MMI manifold - SOLD! (no longer a two boat owner!!) Last edited by sastanley; 03-21-2021 at 12:18 AM. |
The Following User Says Thank You to sastanley For This Useful Post: | ||
ernst (03-23-2021) |
#3
IP: 69.250.109.188
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I had a problem like you describe several years ago. I spent a lot of time troubleshooting the pump (including removal), but it turned out to be that the old bronze water strainer was not sealed tightly. It appeared to be, but I really had to crank down on the bolts to get it air tight. If you messed with the strainer during your pre- or post-winter prep, that could be your problem.
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#4
IP: 99.30.185.198
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I believe that scratchee hit the nail on the head. If there is even the slightest air leak in the intake route, these flexible vane pumps will almost always refuse to pump.
Tom |
The Following User Says Thank You to thatch For This Useful Post: | ||
TimBSmith (03-21-2021) |
#5
IP: 73.163.155.191
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Quote:
However: (1) It worked fine the very last time I turned the motor over, and sucked in the antifreeze through that very strainer in December. Haven't touched it since then. (2) Because of the 'boat on fire' experience I thought of this possibility and tightened down the wingnuts on the strainer very carefully. It is true that its gasket is a bit iffy; I don't remember if I replaced it ~20 years ago) and I am right now looking at finding a replacement. West Marine does not have it in stock and I am now trying to identify what exact model it is so I can order it online. I may ask your advice on that but will do it in a separate thread so people can actually find it. I think this is unlikely to be the problem though because of: (3) I did not mention in my original posting another test I did: I attached a hose directly to the pump inlet, with its other end in a bucket full of water, and then cranked the motor. Again nothing. I admit that this last test is perhaps not a tellling as I thought at the time because of SASTANLEY's point, about a missing prime. So I guess I have to repeat it with (a) the hose into the bucket filled completely with water and (2) the pump filled with water through a funnel, as he suggested. I will definitively report on the outcome of that test. The problem is that each 10-minute test requires nearly two hours time driving to the marina and back. So if there is anything else I should try, please let me know. Could there be comething with the cover plate? It had some grime on it but it is not noticeably scored or anything. The pump is over 10 years old (when I converted to fresh water cooling) but my A-4 gets very little use. A couple hundred hours maybe over that time? Thanks for any tips! Last edited by ernst; 03-21-2021 at 10:40 AM. Reason: I seem to find typos only after I submitted my postings... |
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TimBSmith (03-21-2021) |
#6
IP: 47.142.136.120
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Quote:
Impellers can get a curve memory and become weak or ineffective. How long since the impeller has been changed? Pull the impeller out and see if the vanes are still flexible. ex TRUE GRIT |
#7
IP: 104.174.83.118
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There are several issues that can produce these symptoms and the most common has already been discussed (suction side air leak). Other possibilities are pump cavity wear allowing internal leakage around the impeller vane ends, impeller cover not seated properly, impeller cover gasket or O ring damaged or dislodged, etc. That this happened following a winter the possibility of freeze damage is, in terms of timing, logical.
I'd like to mention though that a mindset of "everything is good because it worked fine the last time it ran" can work against you during troubleshooting. Clearly, everything is not good, we just haven't found it yet. I'd start by removing the hose from the intake thru-hull and opening the seacock. Water should flow generously.
__________________
Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others |
#8
IP: 73.163.155.191
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Quote:
Impeller: It is about 2 years old. I took it out and it seemed perfectly fine: flexible, not deformed, no cracks. I replaced it with another one that I had in my tool box. It was not new but replaced while working, during regular maintenance (did not have a brand new one on board). No difference. |
#9
IP: 73.163.155.191
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Yes, I can do that easily and I should have tried it. But if that really is the problem, shouldn't it have continued to pump after it spurted out the one dollop of water? Still, worth a try.
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