yanmar water pump leaking after replacement

Apr 13, 2015
141
Catalina 309 Tampa
Hey guys - well, I had a leak from the fresh-water pump seal and had started a thread about possibly using an alternative parts source instead of genuine yanmar part. see thread at: yanmar parts alternative

I did wait for the actual yanmar part supplier and replaced with the genuine thing.

Now I have another leak which appears this time to be coming from the O-ring section at the base of the pump. See the attached pic, there's a section of the pump which is like a pipe that slips into the engine block and has an O-ring on it for a seal. In my thoughts, that's not an optimal design, as the other mating ports can be sealed tightly by the bolts holding this on and the gasket with RTV silicone on the gasket. I don't think tightening the water pump beyond the torque specs would help the O-ring seal.

I made sure the surface inside the block the O-ring seals against was clean and lubed the ring with teflon lube before inserting.

It's not leaking much, like 1/2 teaspoon per 45min run...but it's annoying.

I don't think leaks like this tend to just "go away" on their own - do you think differently? I guess I can take the whole thing out again and this time re-install the pump with the O-ring coated with RTV silicone too.

Any other thoughts?

Thanks for any insight - Dave in Charlotte Harbor
 

Attachments

Jul 7, 2004
8,058
Hunter 30T Cheney, KS
Did you use a new o-ring? Sometimes when they are disturbed and the seal is broken, their age becomes apparent. Personally I wouldn't use RTV. You could probably find a new o-ring at a hardware or plumbing supply.
 
Apr 13, 2015
141
Catalina 309 Tampa
Yeah, I probably should have been clearer... the pic is the old pump. I put in a new yanmar pump with a new yanmar o-ring.

I guess I could look for a different o-ring with a bit tighter fit, but what a pain. Every time you remove the pump you have to drain all the coolant.

Thanks, Dave
 

mjsb

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Jan 28, 2021
27
Hunter 31 0 Tampa Bay Sailing Squadron
Just put a new fresh water pump, sending units and t-stat on a 2gm20f, no leaks, and I check every day. However, before doing the install, I scraped the surfaces on the block and the t-stat housing with a razor blade, then I used a waterproof pool grease to hold the gaskets in place while bolting all parts to the engine block, torqued per specs in a diagonal and circular pattern, slow and easy.This is just a suggestion. If it really bothers you get new o rings and gaskets and start over again. Slow and good luck.
 
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Jul 7, 2004
8,058
Hunter 30T Cheney, KS
Could the new pump be old i e. sitting on a shelf for a long time with a bad o-ring?
 
Apr 13, 2015
141
Catalina 309 Tampa
So I guess the o-ring could have been old, but it didn't seem so. However, I didn't carefully examine it as it was "new".

And yes I did carefully clean and scrape the mating surfaces including where the o-ring goes in

Unless this magically stops, I guess the only option is re-do with a new ring, maybe I can find one a tiny bit thicker to seal better.

Dave