Replacment impeller for Oberdorfer not making the grade

[Baltimore Sailor]

Last year I bought a replacement impeller for the Oberdorfer water pump on my late model A4. At the time I noticed that it was about 1 mm shallower than the old impeller. (By that I mean that if you laid the impellers on a flat surface, the old impeller was about a mm "taller.")

I didn't think too much of it at the time, but when I replaced the impeller I right away noticed that it didn't push as much water as the old one, and at low idle in gear the engine got noticeably hotter than usual. I mentioned this here at the time, and Don recommended soaking the new impeller in some MMO and trying again.

Well, I did this, but then I put the new impeller in a ziploc bag in my toolbox and left the old impeller in for the rest of last season, and happily motored the rest of the year. At the beginning of this season I replaced the old impeller with the new, MMO-soaked impeller, and for a while things seemed OK. I still didn't think it was putting out as much water as the old one, but the engine temps were good and since I'd put in a bypass valve I figured that I could always send more water through the block with that.

Now we come to today. I was down at the boat upgrading some rigging (imagine that -- working on actual sailing stuff!), and at the end of the day I started up the engine to give her a warmup, since it had been a week or so since I started her.

Now usually I open the raw water thru-hull first (because she always starts right up), but this time for some reason I forgot. So I started her up and listened to her for a couple of seconds, pushed in the choke and then remembered I hadn't opened the valve -- so I dived below and cranked it open. No more than a minute had gone by.

I noticed that the temp gauge was off the peg already, but I put this down to running dry. I looked over the transom at the exhaust and noticed that it was definitely putting out less water than usual, and the temp was already closing in on 180, when it usually has to run in gear for nearly a half-hour to get that warm.

So I thought great, I've trashed the new impeller by running it dry. But I still had the old one (still looking great: no lobe memory, no cracks, very flexible), so I figured I'd pull the new one and if it had gone, I'd put the old one back in.

When I pulled it out it looked fine; not a thing wrong with it. So, since the old one still looked great I put it back in, and when I fired her up it gushed water as of old and stayed cool.

So, at the end of this long tale, what's my best course? Could it just be that I got a slightly smaller impeller from an odd batch, and that another one would work better? Or have the impellers changed over time so that a 2010 impeller just won't work in a 1975 A4? I'm mighty tempted to just buy a new water pump, but it gripes me to think of laying out more $$ because replacement impellers won't work for me.

One other thing I did notice: when I put the old impeller back in, it extended beyond the pump housing exactly the amount that the new impeller was short, and tightening down the screws compressed everything into place. It seems hard to believe that such a small difference in height could make such a big difference in water flow, but I can't think of anything else that could cause it.

I'm going to keep running with the old impeller, since it looks and feels fine; but I need to resolve this issue for good.

Has anyone else with a mid '70s A4 had any problems at all with replacement impellers in an Oberdorfer water pump?

Thanks!

[hanleyclifford]

bad impeller

Here is another who has had the same problem with replacement, after market, knockoff? Oberdorfer impeller wannabe. Mine didn't last as long as yours, but rather lost a blade almost immediatly. I bought the thing in Annapolis at what used to be the "Viking Boat Supply". What I learned from this is to be careful about what you see in the aftermarket. Now I always take an old unit with me to the store to compare dimensions.

[Baltimore Sailor]

Well, the bad thing about mine is that I bought it from here.

Maybe I should take my old one in to a store and see if I can find one with the same height.

[hanleyclifford]

replacement impellers

If you got that impeller from Moyer Marine you should report this to whomever in the organization handles procurement. A very unsettling development. On this type of pump the fit against the back plate must be tight.

[roadnsky]

Well, the bad thing about mine is that I bought it from here.

BS-
Is there a reason you haven't called Ken or Don to ask about this?
MMI has the best customer service I've experienced in ANY industry.
AND, I know Don would want to know if there were an issue lurking...

[Baltimore Sailor]

Well, yes I did, and Don made the suggestion about soaking the impeller in MMO. I haven't followed up on it since then, mainly due to laziness on my part and having a functioning impeller to fall back on.

I really should talk to someone about this officially, I suppose. It's not doing me any good sitting in the tool kit.

[Dave O]

I would like to know more about it. I replace the impeller every season just to avoid any problems. So if a new impeller is an issue it defeats that purpose and costs time, money and peace-of-mind.

[jhwelch]

If an engine is being used frequently is it necessary to replace the impeller?

That is, there is no long period of time where it is sitting, so the impeller doesn't
take a "set".

I remember the day I was tooting along in a skiff and the 20+ year old outboard
motor conked out -- the impeller had finally given up the ghost.

-jonathan

[hanleyclifford]

giving up the ghost

The problem with running an impeller until it "gives up the ghost" is that it might also be inclined to give up some of its body parts and scatter them amongst the area it used to love, your engine. An amputated impeller blade can block an artery almost anywhere in the system. The problem with the flexible impeller is that it will weaken over time even if used regularly. This is especially true in salt water. Still, there will always be reports from mariners who have used an impeller for many years without incident. So as they say out there in California; "you have to ask yourself one question, do you feel lucky?"

[Kelly]

...and then, "Well, punk, do you?"

[hanleyclifford]

Actually I have run an impeller for 15 years in my dinghy engine (4 hp Evinrude), but I always have my oars with me. The inspector also said,"man has got to know his limitations".

[will]

Last year I bought a replacement impeller for the Oberdorfer water pump on my late model A4. At the time I noticed that it was about 1 mm shallower than the old impeller. (By that I mean that if you laid the impellers on a flat surface, the old impeller was about a mm "taller.")

I didn't think too much of it at the time, but when I replaced the impeller I right away noticed that it didn't push as much water as the old one, and at low idle in gear the engine got noticeably hotter than usual. I mentioned this here at the time, and Don recommended soaking the new impeller in some MMO and trying again.

Well, I did this, but then I put the new impeller in a ziploc bag in my toolbox and left the old impeller in for the rest of last season, and happily motored the rest of the year. At the beginning of this season I replaced the old impeller with the new, MMO-soaked impeller, and for a while things seemed OK. I still didn't think it was putting out as much water as the old one, but the engine temps were good and since I'd put in a bypass valve I figured that I could always send more water through the block with that.

Now we come to today. I was down at the boat upgrading some rigging (imagine that -- working on actual sailing stuff!), and at the end of the day I started up the engine to give her a warmup, since it had been a week or so since I started her.

Now usually I open the raw water thru-hull first (because she always starts right up), but this time for some reason I forgot. So I started her up and listened to her for a couple of seconds, pushed in the choke and then remembered I hadn't opened the valve -- so I dived below and cranked it open. No more than a minute had gone by.

I noticed that the temp gauge was off the peg already, but I put this down to running dry. I looked over the transom at the exhaust and noticed that it was definitely putting out less water than usual, and the temp was already closing in on 180, when it usually has to run in gear for nearly a half-hour to get that warm.

So I thought great, I've trashed the new impeller by running it dry. But I still had the old one (still looking great: no lobe memory, no cracks, very flexible), so I figured I'd pull the new one and if it had gone, I'd put the old one back in.

When I pulled it out it looked fine; not a thing wrong with it. So, since the old one still looked great I put it back in, and when I fired her up it gushed water as of old and stayed cool.

So, at the end of this long tale, what's my best course? Could it just be that I got a slightly smaller impeller from an odd batch, and that another one would work better? Or have the impellers changed over time so that a 2010 impeller just won't work in a 1975 A4? I'm mighty tempted to just buy a new water pump, but it gripes me to think of laying out more $$ because replacement impellers won't work for me.

One other thing I did notice: when I put the old impeller back in, it extended beyond the pump housing exactly the amount that the new impeller was short, and tightening down the screws compressed everything into place. It seems hard to believe that such a small difference in height could make such a big difference in water flow, but I can't think of anything else that could cause it.

I'm going to keep running with the old impeller, since it looks and feels fine; but I need to resolve this issue for good.

Has anyone else with a mid '70s A4 had any problems at all with replacement impellers in an Oberdorfer water pump?

Thanks!

Baltimore - I am have had the same experience, impeller from MM, after 3 lost weekends trouble shooting the cooling system, put old back in, flow was fine. Just put in the cam "swipe" that MM has for the pump, it is much thicker than the 37 yr old one I removed. A one min. job, one screw. Jury is out, still on the hard in Sandusky. Check MM's site for gpm flow rate. I hooked a temp. hose to the pump to a drywall bucket with gal. increments I marked on it. 3 gpm I recall, but check. I also have a tee fitting from Prestone in my fresh water intake to prime the pump while in dry dock for the spring start up.( also I add antifreeze this way ) Sometime the fixed intake will get air bound when I put in, so I carry a 4 ft piece of garden hose with me for priming or filling. In about a week I will pump out the antifreeze and flush and will be able to tell from the same bucket in the cockpit how it will or will not be working. I catch the antifreeze with another bucket at a temporary elbow at the exhaust.

Will advise

Will

[Baltimore Sailor]

I just today received a replacement impeller from Steve Moyer, without even officially asking. Just another great example of the customer service at MMI.

Steve included a note saying that factory specs for the impeller are 7/8" in height, so Friday when I get back over to the boat I can compare the new one with the "old" new one in my tool box, and see how they match up.

I'll keep the forum posted.

Thanks, Steve!

[minx27]

Similar problem?

Hi A4 Community:
Having just replaced the impeller on my '75 A4 Oberdorfer water pump I was dismayed to observe very little flow from the exhaust and the temperature just shooting up like crazy. After some research here I think I may have bought one of these not-quite -right impellers , too. My question: should I pull the pump and replace the cam shoe? Will a new impeller from MM be the right size? I surely don't want to go through this again....
Thanks,
Dot
Minx27

[Don Moyer]

We receive a handful of reports each year in which an older Oberdorfer impeller has swelled to a size considerably larger than the dimensions of a new impeller. If an impeller is kept in service until it enlarges significantly beyond its original size (particularly in width), it will cause accelerated wear on the inside of the impeller chamber. In some few cases, assuming the impeller itself survives, wear within the impeller chamber will so closely match the aging/swelling impeller that the pump will continue to function longer than expected. Unfortunately, these pumps will usually not accept a new (properly sized) impeller.

New Oberdorfer impellers measure 2” in diameter, and 7/8” across the width. If your pump will not work with a new impeller with these nominal dimensions, you have several options:

1) Reinstall the old impeller and continue to use the pump (not really recommended except as an emergency measure to get to a safe port).
2) If you have an older Oberdorfer M3 series pump (usually with big raised letters on the back plate), you can try replacing its cam shoe with a new M7 shoe (product number - CSOB_08_69 in our online catalog at moyermarine.com). The M7 cam shoe is twice as thick as the M3 (1/8” versus 1/16”). The increased performance of the M7 shoe might allow the pump to continue working, at least as an emergency spare.
3) If wear within the impeller chamber shows up primarily as excessive depth, you might be able to work enough metal off the rear face of the housing (using sand paper on a flat surface) until seeing a small amount of “crush” on the new impeller when installing the back plate. In these cases, you will probably also have to reface the back plate using the sand paper on a flat surface to get rid of any grooves.
4) Replace the pump and begin changing the impeller after every second season or after 200 hours whichever comes first (after every third season or 300 hours for freshwater cooled engines).