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SS U-Mixing elbow

Oct 29, 2005
2,051
Hunter 326 Singapore
I've uses the HDI SS U-Mixing elbow for last 3 good years. Each year I remove and check, no fouling. Just last year I noted some rust stain. Didn't think much about it and clean it.
This year I noted more stain and closer, it looks like chloride stress corrosion. Small putting and crack lines. Has anyone same problem?

Ken Y
 

capta

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Jun 4, 2009
3,753
Pearson 530 Admiralty Bay, Bequia SVG
That's why the good ones are made of Monel. Ours is over 30 years old and good as new.
 
  • Helpful
Likes: ggrizzard
Jan 4, 2006
2,879
Hunter 310 West Vancouver, B.C.
This year I noted more stain and closer, it looks like chloride stress corrosion.
Hi Ken. Installed mine two years ago and have not taken it off yet to inspect. With this bit of news, I will remove it now to see what's going on if anything. Rust stain should not appear and I very much doubt it would be a precursor to stress corrosion. Cases I've dealt with are without colour. Mind you, most anything is possible with the right environment.

I'll post internal pictures with my newest borescope if/when it arrives.

Have you contacted the people at HDI Marine ? I'm sure they'd be all over it if there was a problem.
 
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Likes: ggrizzard
Oct 26, 2010
1,065
Hunter 40.5 Beaufort, SC
That's why the good ones are made of Monel. Ours is over 30 years old and good as new.
I think mine is Monel too - 1994 Hunter 40.5 - I called HDI awhile back about the ability to get a replacement (just anticipating possible future needs). I told them I had a Yanmar 4JH2E and HDI didn't make a SS one for that model. I asked why and they said to check the elbow as it was probably Monel and that it should be non-magnetic and a "dull bronzish color" if I scrape it a little. If it is he said it should last a long long time. Sure enough it is non-magnetic and a dull bronze/yellow (not brass though) color. It was painted "dull gray" for some reason. I'm not sure if all 4JH2E Yanmars of that vintage are the same but I was sure happy with mine did.
 
Oct 26, 2010
1,065
Hunter 40.5 Beaufort, SC
That's why the good ones are made of Monel. Ours is over 30 years old and good as new.
Justin mentioned occasional cleaning - do you remove and clean yours on some periodic schedule?
 

capta

.
Jun 4, 2009
3,753
Pearson 530 Admiralty Bay, Bequia SVG
Justin mentioned occasional cleaning - do you remove and clean yours on some periodic schedule?
Nope, never have in ten years. When I had it off about 5 years back for another reason, it was as bright and shiny inside as out.
I believe those who periodically check theirs are used to the metal ones that rust and only last a few years. Old habits die hard?
 
Jul 7, 2004
6,668
Hunter 30T Cheney, KS
I'm not sure if it was the engine tune, lugging the RPMs or what, but some folks have shown heavy carbon buildup.
 

SFS

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Aug 18, 2015
1,755
Hunter 31 Tampa Bay
I'm not sure if it was the engine tune, lugging the RPMs or what, but some folks have shown heavy carbon buildup.
We put about 500 hours on our HDI SS elbow in the 8 months we were on the boat after its installation. For the last part of the final journey home, I noticed a somewhat decreased water flow out the exhaust (and some grey smoke), but none of the usual culprits (pump and hoses) were a problem. One day I was trying to make a scheduled bridge opening and ran pretty close to WOT for about 45 minutes. Afterwards, no more grey smoke, and water flow back to normal.

I had mistakenly assumed that our cruising throttle setting (2850 rpm) qualified as a "high throttle setting" According to the manual, max RPM was 3600 (Yanmar 3YM20). Turns out 78% RPM was not a high enough settng to prevent that carbon buildup.
 
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Likes: DArcy
Jul 7, 2004
6,668
Hunter 30T Cheney, KS
Good input. We never really get a reason to "open her up" on our pond, but I should do it anyway.
 
Oct 26, 2010
1,065
Hunter 40.5 Beaufort, SC
Good input. We never really get a reason to "open her up" on our pond, but I should do it anyway.
I've always practiced a routine that I think helps reduce carbon build up. On the return to the mooring about 15 to 20 minutes out I open her up to WOT (3600 rpm) for about 5 minutes. I do this each time and then come back down to cruise speed (about 2750 rpm) for the remainder of the return until I"m a few minutes out from the mooring and slow down to 1000 rpm or so to let it cool down. After I'm on the mooring it takes a few minutes to get things settled in so I go to full idle and only then do I shut it down. Seems to work for me.
 
Jan 4, 2006
2,879
Hunter 310 West Vancouver, B.C.
Hang on Ken. Headed out to the boat today, will pull mine and stick my nose in it.
Got to the boat and found I had no riser gaskets :angry:. Always have an extra on board with the engine spare parts. Checked with local supplier and was told "no go" as they are currently out of stock. I will check the elbow and let you know as soon as I can scare up a gasket, or the world comes to an end. No guarantees here :yikes: !
 
Oct 29, 2005
2,051
Hunter 326 Singapore
After cleaning up the outside of the U-Mixing elbow (no need to clean inside 'cos its very clean, see photo) I don't have access to any welding equipment so I patch the fine cracks with Q-Bond and spray paint. Hope it works.

Ken Y
 

Attachments

Jan 4, 2006
2,879
Hunter 310 West Vancouver, B.C.
1. Did you test to see if the external signs of corrosion went through the casting to the interior ?

2. Did you ever contact HDI Marine to get their take on this problem ? I'm sure they'd be interested.
 
Oct 29, 2005
2,051
Hunter 326 Singapore
1. Did you test to see if the external signs of corrosion went through the casting to the interior ?

2. Did you ever contact HDI Marine to get their take on this problem ? I'm sure they'd be interested.
Qn1- the water droplets was brownish-black, and could only comes from inside.
Qn2- nope. Doubt they can do anything for me from so far away.

Ken Y