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!

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???

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 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

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.

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!

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

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.

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.

Replies in red

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/

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

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.

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.

It has happened before . . . .

This also speaks to the importance of keeping the face plate gasket thin.

One last tidbit
 

Before installing the pump cover, I always lubricate the inside of the pump with either liquid hand or laundry soap. It does two things, first, it tends to close small gaps which will increase it's tendency to pump and secondly, it will lubricate it until it is actually pumping liquid.
Tom

I always had problems with those paper thin gaskets getting mess up while I put the face plate on. I have since found that two small binder clips will hold the gasket to the face plate until the screws are started, then the binder clips can be removed and the face plate tightened.

Wow! That's sure more than a few thou!

I have a fruitful day behind me. I think you nailed the problem, it was at the very beginning. And, embarrassingly, it is possible that I messed it up myself...

But, do let's start at the beginning. First, I sanded the inside of the pump cover to make it nice and shiny, can't hurt. Then I did exactly what NDUTTON said, make sure water flows freely from the strainer. Well, it did not. I had the bad idea of sucking on the hose -- and got a mouthful of antifreeze. :eek: I got slightly wiser and used a small utility pump to suck on the hose but still no water.

Then I looked at the installation and noticed something which may be crucial. A long time ago (15 years?) I installed a nifty contraption that makes winterizing the cooling system very convenient: I installed a T that feeds into the strainer, with one input the seacock and the other a hose that I can put into a bucket with antifreeze. I put a valve in this hose which is usually closed. To winterize, I open the valve and close the seacock and the raw water pump sucks the bucket empty. Winterizing done!

What I now noticed is that I put this contraption (valve and T) just above the strainer (because it fits there...). I realized the top of the strainer is exactly at the water level, and the inlet of the pump is just below that (less than an inch). Now I wonder whether that is carefully designed to be that way. The problem (if it is one) is with my patent winterizing apparatus I have now several feet of hose an inch or two higher than the water level.

I have never had a problem with that but could it be that for some reason, this hose always remained filled with water EXCEPT for this winter, when the hose fell dry for some reason and therefore the pump was not primed? I thought I had excluded that possibility because, as I wrote in an earlier message, I had attached a hose to the pump inlet with its other end in a bucket of water that I held above the pump, and it STILL did not work. What I had NOT done, however, was to fill this hose with water! Since the pump is not self-priming, I suppose this 'test' was not really valid.

In any case, what I did today was to bypass the whole winterizing shebang and attached the hose from the seacock directly to the strainer inlet. Indeed, now the pump inlet was just below the water level. And water did flow when I opened the seacock!

Well, the rest was easy. I installed a new impeller (Globe run-dry) and gasket and turned over the motor. Water came out of the pump outlet immediately. I connected the hose to it and the motor was cooled just as it was supposed to be.

So, was that a major blunder that I committed with my clever (??) :rolleyes: winterizing system? Should I be thankful that the problem occurred when I was safely in a slip, and not in some critical situation?

Or is it OK to have that hose above the waterline?

BTW, since I had brought all the tools I thought I might need, including a caliper, I did measure the old and new impeller and the pump cavity. The results were a bit surprising (to me). The new impeller measured 21.95mm (I find mm easier to use for this purpose, others may disagree) and the old one essentially the same, the caliper showed 21.93mm. This is rubber after all so I guess this difference is meaningless. But I was surprised by the depth of the pump body which I measured as 22.25mm. So it is about 0.3mm larger than the impeller. or a bit more than 10 thou. I was expecting it to be smaller. But the pump is pumping like a champ so I won't complain :)

Do you think I solved the problem? And should I do something about my winterizing system?

Thanks!

Great idea! Next time...

Actually, these pumps WILL self prime when they are in newer, less worn condition. Your measurements indicate cavity wear (completely normal and expected as the pump ages) which explains its inability to self prime anymore. Because of that, designing the raw water intake path to be entirely below the waterline would help matters in the current situation.

But so would a new MMI 502 raw water pump that doesn't have cavity wear and will prime itself readily. Your pump is telling you it's about time to retire.

I don't know long the impeller was turning inside the pump dry. A dry impeller turning inside a pump will generate a lot of heat which can lead to shortened impeller life.
I finally got to the place where I primed the pump every time after I had it apart. It cut down on the "drama".

ex TRUE GRIT

Good to know! So it looks my installation was not as stupid as I feared.

I am a bit surprised though that the pump already has considerable wear. As I said, this pump is not that old, it came new with the freshwater cooling system from Indigo that I installed 10 years ago (maybe a bit more). I haven't checked the hour meter but I guess the pump has only a few hundred hours on the clock. I use the Globe Run-Dry impeller for this pump (but NOT for the coolant side), could that have to do with the wear?

I think I will re-design the winterizing system. Thanks for all your help!

I hope I won't have to do that :(

The longest time this impeller ran dry was when this event occurred, so this cannot have caused it. It does not look damaged at all. FWIW it is a Globe Run-Dry impeller so maybe that helped.