Heads Up on M25 Replacement Impeller

scgunner · April 19, 2021, 07:24:19 AM

This concerns the Oberdorfer water pump on the M25, I'm not sure if later model motors use the same pump or not.

End of last season I did a 100hr service which included impeller replacement. Upon completing this service I usually do about a 30min run in to make sure everything is working properly, which it was, including cooling water moving through the exhaust. To start the season I usually do a motor run up to make sure it's working properly, which it normally is. This time however these was no water blowing out the exhaust.

What I found when I pulled the pump cover was the brass bushing on the pump shaft was spinning but the rubber impeller wasn't. The bond between the two had broken so the impeller wasn't turning. I've probably replaced 20 impellers over the years and this is a first. I went to my local chandlery and got a new one, I asked about this and the guy said there may have been a bad batch, but he wasn't sure.

I've used a lot of these impellers and I'll still rate it as extremely reliable, but if there was a bad batch and you are changing or have recently changed your impeller I'd keep an eye on it at least until you've got several hours on it. And keep a spare handy.

Kevin Griffith · April 19, 2021, 08:31:14 AM

I have a 1989 C-34 with M-25XP engine. Last season I got tired of dealing with the old Sherwood pump and changed to the Oberdorfer M202M-837/908 (Depco). The impeller failed just as you have described after only 10 hours of operation. I replaced the impeller with a replacement that I had purchased at the same time as the pump and it was also defective. The next replacement lasted the rest of the season. I think they must have had a manufacturing issue but there may be a lot of those defective impellers out there.

Stu Jackson · April 19, 2021, 10:34:24 AM

Could you be more specific, please.

Were these Oberdorfer impellers or others, like Globes?

Would be helpful to know.

My experience over 24 years has been no issues using the black Oberdorfer impellers. Could well be a recent manufacturing defect.

Very, very good idea to check, always, thanks for the reminder.

Ron Hill · April 19, 2021, 02:39:02 PM

Kevin : Some times those impellers sit on the shelf too long and "dry out". Also there could have been a manufacturing glitch??

I always found it best to buy from someone that sell a volume of impellers like Defender. You can choose the black ones or the Globe. I personally always buy the globe.

With the black ones I always recommend squirting some silicone spray on them to keep them nimble.

A few thoughts

Kyle Ewing · April 19, 2021, 02:53:59 PM

Ron--Is there a shelf-life or way to tell if it's dried out? I found a new impeller I forgot I had. I don't want to use it if it'll fail soon and don't want to throw-out a good part.

Ron Hill · April 19, 2021, 03:09:48 PM

Kyle : Take your finger and bend the blades back one at a time. If you see a crack or cracking - that impeller is bound to fail.

The problem of the "rubber" debonding itself for the brass in the center, I believe is most likely a manufacturing flaw. This is not a common impeller failure!!

A thought

scgunner · April 19, 2021, 05:09:51 PM

Stu,

Excellent performance from the impeller has been my experience as well, that's why I wanted to give you guys this heads up.

Information wise here's what I know. I have been buying impellers from my local chandlery, The Captain's Locker, since I got Top Gun in 1988. They are a supplier for Oberdorfer as well as Universal and are known locally for their knowledge and the quality of their parts. I can't say for sure if the impeller is OEM or aftermarket since it comes unwrapped with only a numbered sticker on it. If I have to guess I'd say it's Oberdorfer based on their reputation and the fact that it cost 50 bucks. If it was a cheap Chinese knock off I'd think it would cost less than half that. That's what I know.

Ron,

The impeller looked pretty fresh, I don't think it sat on the shelf very long, these guys are usually pretty busy. I've never heard of Globe before I just always assumed I was getting an Oberdorfer, and I agree this is not common, in 33 years it's a first for me.

KWKloeber · April 20, 2021, 09:08:49 AM

The word from my distributor:

Yes, Oberdorfer is aware of the issue.
They had a large batch that was bad.

I don't know if folks are aware, but Ob has been a mess lately. The "small" hometown NY company was sold, then bought out again, and production up and moved with little planning and zero preparation as far as stocking up to take up the slack before production could be ramped up again. Then COVID-19 hit.

So, it's not your father's Oberdorfer anymore.

scgunner · April 20, 2021, 11:33:35 AM

Ken,

Thanks for your heads up. I'll keep an eye on mine and keep a spare handy!

mark_53 · April 22, 2021, 10:07:53 AM

Quote from: Stu Jackson on April 19, 2021, 10:34:24 AM
Could you be more specific, please.

Were these Oberdorfer impellers or others, like Globes?

Would be helpful to know.

My experience over 24 years has been no issues using the black Oberdorfer impellers. Could well be a recent manufacturing defect.

Very, very good idea to check, always, thanks for the reminder.

I have had the same problem with the black impeller. Don't remember the brand. Collar spins but impeller doesn't. I changed to blue and no problems yet.