yanmar water pump leaking after replacement

Apr 13, 2015
156
Catalina 309 Port Charlotte
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
8,402
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
156
Catalina 309 Port Charlotte
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
56
Hunter 31 0 TSS, Apollo Beach FL
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.
 
Last edited:
Jul 7, 2004
8,402
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
156
Catalina 309 Port Charlotte
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
 

Dan_Y

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Oct 13, 2008
514
Hunter 36 Hampton
Dave-
Thanks for posting this and the PM for me since I have the same issue.
The latest Yanmar 3YM30 parts manual calls for a JASO-2028 oring for 2012 and newer engines and a JIS P26 in pre 2012. My engine is from 2008 and so should use a P26 oring. The 2028 is 27.70 mm ID x 2.4 mm cross section, made of nitrile, while the P26 is 25.7mm x 3.5 mm, made of Buna-N. I replaced the freshwater pump 4 years ago and the oring dripped a little but not enough to pull the pump again. But this spring the shaft seal started leaking so I replaced the pump again and used the oring that came on the new pump. Used plenty of ptfe oring grease on the block and oring during anssembly. Odd the 4 year old pump leaked. shaft bearings were good and belt not over tightened. I flushed the cooling system to look for sediment that could grind up the shaft seal in the pump but didn’t notice much sediment. The oring dripped about a tablespoon of coolant in about 10 minutes once the engine warmed up and the cooling system pressurized. After removing the new pump again, the oring measured to the P26 specs…ugh.

I burnished the sealing surface in the block with 1200 grit being careful to remove only rust and dried coolant before putting in the new pump. But now that the pump is out again, I notice two areas of small pitting on the sealing surface in the block. Assuming the oring is correctly sized, the pits could cause leaks I guess, but why so much with a new pump/oring???

Two desperate solutions come to mind. First is to wipe on a super thin coat of JB Weld steel epoxy to fill in the pitting on the block. After burnishing that, apply permatext 22701 water pump RTV gasket maker or 89145 ultra gray RTV to the block surface where the oring seals and to the water pump oring, reassemble and let harden for 24 hours. I have a new P26 oring on order. Should have looked at the auto parts store first.

Any better solutions out there?

thank you,
Dan_Y
 

Dan_Y

.
Oct 13, 2008
514
Hunter 36 Hampton
Update to my last post above.
To make a good oring seal on the Yanmar 3ym30 water pump:
1. I applied the super thin layer of JB Weld in the block then sanded smooth with 1200 grit. All pits were filled and mostly clean steel was left after sanding.
2. Before placing the oring on the pump I took a piece of Teflon plumbers tape, folded it in half lengthwise so it would fit in the oring groove, and made two turns around the water pump nipple.
3. When assembling I “lubricated” the oring in Permatex 22701 water pump RTVsince it’s made for contact with antifreeze. A thin layer of 22701 was also applied to the sealing surface in the block. The pump was then bolted up tight.

The 22701 requires 24 hours to cure. I let it set for a week then assembled the two water heater fittings. I experimented with Teflon tape on one fitting and the unused 22701 for the other-like pipe dope.

No leaks after an hour of run time.
Dan