How can a simple impeller pump fail completely?

[ernst]

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!

[sastanley]

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???

[scratchee]

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.

[thatch]

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

[ernst]

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???

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.

[ernst]

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.

I have had that happen, too, with quite dramatic effect! A few WEEKS after I bought the boat, I cleaned out the strainer (being extra diligent, as a new boat owner!) and the went out with my wife and 3-year old son (who graduated from college last year, so that gives you a timeline ). I was not well attuned to the boat so I missed that the temp gauge was creeping up (no auditory alarm, added one later). Sure enough, at some point there was hot steam rising out of the engine compartment (my wife still refers to this event as 'when our boat caught on fire' ) and the motor stopped. The good thing that came out of this is that I learned how to replace the head gasket

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!

[JOHN COOKSON]

(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.
Thanks for any tips!

These pumps can have a problem with dead lift. Place the bucket higher than the pump and then prime.
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

[ndutton]

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.

[ernst]

These pumps can have a problem with dead lift. Place the bucket higher than the pump and then prime.
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

Place bucket higher: Excellent point. Will do!

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.

[ernst]

Replies in red

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 would not except substantial wear giving the age of the pump. But how could I test for that? Would that be visibly obvious ?

impeller cover not seated properly: Same question.

Impeller cover gasket: Yes, the paper gasket is a bit damaged. I had put some goop on it and I tightened it very well yesterday, certainly not gap visible. Of course I will replace it. But will that really make the pump not work AT ALL, not even against a head of 1"? (with outflow hose removed?)



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.


You are right, of course!

I'd start by removing the hose from the intake thru-hull and opening the seacock. Water should flow generously.


Haven't done that but will do (easy). But it did not work with the bucket either.

Give than my overhead for each troubleshooting is 2 hours (way to and from marina), can we assume that the water is flowing freely? If it is not, I know where to look. But what should I do next that assuming water IS flowing freely?

[ronstory]

If you have a leaky backplate it will be easier for the impeller pull-in the easy-breezy air then try to suck up heavy liquid stuff. It would be like the opposite of priming the pump.

The gasket is pretty thin and if you wanted to make a quick and dirty gasket to test, sacrificing a $1 bill is actually great gasket material. It's about 4-5 thousandths thick and very durable... since that pesky paper money can survive the accidental laundry excursion.

Good luck.

[ernst]

If you have a leaky backplate it will be easier for the impeller pull-in the easy-breezy air then try to suck up heavy liquid stuff. It would be like the opposite of priming the pump.

The gasket is pretty thin and if you wanted to make a quick and dirty gasket to test, sacrificing a $1 bill is actually great gasket material. It's about 4-5 thousandths thick and very durable... since that pesky paper money can survive the accidental laundry excursion.

Good luck.

Yes, I heard about that trick before.

But I am pretty sure I have a pristine new gasket in my basement, I just did not have it on the boat. Should I be out of them, I know where to get'em: https://moyermarine.com/product/wate...m-csob_06_192/

[Sam]

Some years back I cut a water pump gasket out of grocery store paper bag - worked fine till I received a few from Moyer.

[ndutton]

Ernst, my approach would be to start at the source (thru-hull), confirm that it is clear and shipping water, then follow the path until it stops. Nothing is good until it tests good.

As for the pump cavity, the way I've checked mine (before I replaced it with a MMI pump) was to measure the width of the impeller and the depth of the cavity with a dial caliper. You want the impeller to be a few thousandths wider than the cavity is deep so when you install the cover plate the edges of the impeller vanes are slightly 'crushed'. Of course, you'll want a good impeller and cover gasket. Shopping bags and dollar bills will work but should be considered temporary measures.

If nothing is apparent, I'd get out the pressure gauge/Schrader valve apparatus (available at Home Depot for cheap, see picture) and compressor or hand pump to test portions of the system. For example, you can remove and plug the hose from the thru-hull, attach the gauge/valve to the outlet of the pump and charge it to say, 10 psi. See if it holds pressure. If not, a squirt bottle with diluted dish soap sprayed on everything will tell you in an instant where the leak is. It'll foam up like a 5 year old blowing bubbles.

Finally, if my boat were a 2 hour drive away I'd load up the truck with everything I'd need and a few extras for all the tests mentioned and I wouldn't leave until the culprit was found. Hell, I'd do that if my boat were 15 minutes away. Anything I didn't have with me, I'd go buy.

[ernst]

Thank you! I love your systematic way to approach this! And I had no idea that we are talking thousands of an inch for these floppy rubber parts.

I hope that I can get away on Thursday and see what is going on. This would be good because the marina wants me out of the slip by Friday (I am there only for the winter and need to go back to my 'home slip').

I will surely keep everybody updated what I'll find.