Time for the Monthly Mixing Elbow Question...

[jaysweet]

I have a 17 year-old Yanmar 2GM20F with really low hours: maybe 400. I've been getting just a whiff of exhaust smell now and then: nothing definitive, but enough to make me wonder. I've never had the mixing elbow off before, but for the past few years, there's been an odd rust spot on the side of it, as you'll see in the first picture below. I took it off today. My basic impressions: the 4 exhaust manifold bolts look shiny and brand new, but maybe(?) they came off a little too easily? So it's possible there was a small leak in the manifold-to-engine gasket, maybe because it wasn't tight enough? The other possibility is that there might be a pinhole leak where the big rust spot is on the side of the mixing elbow.

Looking inside the elbow, it really doesn't look too bad to me. I don't think it's too coked up. So my options seem to be: 1) buy a new gasket and put the elbow back on, or 2) buy a new elbow. I think the only reasons for getting a new elbow would be if I think there's a pinhole leak (but how can I be sure?), or just because I have it off and it's been 17 years. What do you all think?

 

[Don S/V ILLusion]

As it's off, take it to a local bike shop or other service center and have it cleaned at which point a pinhole will probably be obvious. They can also pressure test for leaks. A new gasket is needed regardless

 

[Ralph Johnstone]

Pretty much guaranty it's got a pinhole at 17 years of age. Doubtful you're smelling the exhaust past the gasket coming from inside the cabin as the engine air intake will suck that up pretty quickly. With the shape of the transom, it's not uncommon to get a slight smell of exhaust anytime depending on the wind.

Here's the inside story:

If I had to guess, it looks like the pinhole is just to the right of the divider which seems like an odd place seeing as only exhaust gas touches that point. It is what it is !

You may want to take a defibrillator with you when you go to purchase another one. This is one is from 2012 in CAN $$$.

 

[pipedream]

Here are pics from replacing my volvo exhaust. This occurs about every 600 hours or so, and they never look plugged up...

Luckily I heard about another company that sells stainless replacements for much less than the originals. Give HDI a look.

 

[dlochner]

If you even suspect a pinhole, replace the elbow. I had similar symptoms on a Volvo motor and downplayed it. That was a mistake. It broke open while motoring about 15 miles offshore in the middle of a shipping lane with absolutely no wind. Fortunately this happened after the thunderstorms passed. It was a long slow tow to a marina.

HDI is a good source for a new elbow.

VP Stainless Steel Exhaust Elbow - HDI Marine

This HDI Marine Item Replaces: P/N 840690

hdimarine.net

 

[jaysweet]

As it's off, take it to a local bike shop or other service center and have it cleaned at which point a pinhole will probably be obvious. They can also pressure test for leaks. A new gasket is needed regardless

Thanks, Don. Question about the gasket: it looks like several layers crimped together, since I think there's some left on the engine, definitely some left on the exhaust manifold, and I have a nearly intact looking bit that came off as one piece.

 

[jaysweet]

Pretty much guaranty it's got a pinhole at 17 years of age. Doubtful you're smelling the exhaust past the gasket coming from inside the cabin as the engine air intake will suck that up pretty quickly. With the shape of the transom, it's not uncommon to get a slight smell of exhaust anytime depending on the wind.

Here's the inside story:

If I had to guess, it looks like the pinhole is just to the right of the divider which seems like an odd place seeing as only exhaust gas touches that point. It is what it is !

You may want to take a defibrillator with you when you go to purchase another one. This is one is from 2012 in CAN $$$.

I've seen your picture before in the forum: that particular one doesn't look all that bad, actually! I wasn't too certain that the exhaust smell is coming from inside the boat because it isn't all that strong, but I do tend to think that it's real. But yeah: after reading through the replies, I think I'll be replacing it.

 

[jaysweet]

Here are pics from replacing my volvo exhaust. This occurs about every 600 hours or so, and they never look plugged up...

Luckily I heard about another company that sells stainless replacements for much less than the originals. Give HDI a look.

Interesting to hear that low engine hours doesn't mean it's good to go (although the Volvo is a different engine). I've certainly read about the stainless replacement. There's a diesel mechanic in our marina who told me he'd go with the original cast iron b/c it's hard to get the stainless one tightened down enough to avoid leaks. So that's one point of reference, but OTOH, it seems like the forum is filled with people who've used the HDI part and have been happy with it. At least I have it off, so I can use the big old vice in my shop to hold the one half while I torque on the other.

 

[jaysweet]

If you even suspect a pinhole, replace the elbow. I had similar symptoms on a Volvo motor and downplayed it. That was a mistake. It broke open while motoring about 15 miles offshore in the middle of a shipping lane with absolutely no wind. Fortunately this happened after the thunderstorms passed. It was a long slow tow to a marina.

HDI is a good source for a new elbow.

VP Stainless Steel Exhaust Elbow - HDI Marine

This HDI Marine Item Replaces: P/N 840690

hdimarine.net

Looks like I'm headed for the replacement route, Dave. "Only" $194 for the HDI elbow.

So I just checked out your blog. Hope your trip is going well. Did you stay inside all the way down to Florida, or head out into the Atlantic?

 

[dlochner]

Looks like I'm headed for the replacement route, Dave. "Only" $194 for the HDI elbow.

So I just checked out your blog. Hope your trip is going well. Did you stay inside all the way down to Florida, or head out into the Atlantic?

Check out the price for a genuine Yanmar. $198 will seem cheap.

No we haven't gone outside except for a short hop into Savannah River. Tides and wind have not be cooperative and I belong to the "Gentlemen don't sail to weather" school.

 

[Ralph Johnstone]

At least I have it off, so I can use the big old vice in my shop to hold the one half while I torque on the other.

Remember that the coupling has a CW thread on one end and a CCW thread on the other end.

 

[MikeHoncho]

I replaced the whole thing with a replacement from HDI about three months ago. Couldn't be happier. Just replace all of it, manifold, elbow and coupler along with the exhaust hose to muffler. Its to much of a pain to get it apart to not do so. The HDI bill was around $300 for all of it.

 

[jaysweet]

Remember that the coupling has a CW thread on one end and a CCW thread on the other end.

Right. At least the threads are big and obvious...

 

[jaysweet]

I replaced the whole thing with a replacement from HDI about three months ago. Couldn't be happier. Just replace all of it, manifold, elbow and coupler along with the exhaust hose to muffler. Its to much of a pain to get it apart to not do so. The HDI bill was around $300 for all of it.

When I ordered the HDI elbow just now, I did see the whole 3-piece thing there for something like $335. But I think the manifold looks like it's in really good shape (as well as the coupler, which comes with the elbow anyway), so I just went the cheaper route. Who knows: I may regret it.

So also: what do you guys use on the manifold-to-engine gasket, anyway, goop-wise? Nothing? Hi-temp exhaust sealant? Anti-seize seems to be the consensus for the coupler.

 

[dlochner]

Yes, use a high temperature pipe dope. Bostick's Never Seize is one such product, available at McMaster Carr.
It is a bit pricey, but lasts a long time. I still have the can I bought 20 years ago.

 

[pipedream]

Interesting to hear that low engine hours doesn't mean it's good to go (although the Volvo is a different engine). I've certainly read about the stainless replacement. There's a diesel mechanic in our marina who told me he'd go with the original cast iron b/c it's hard to get the stainless one tightened down enough to avoid leaks. So that's one point of reference, but OTOH, it seems like the forum is filled with people who've used the HDI part and have been happy with it. At least I have it off, so I can use the big old vice in my shop to hold the one half while I torque on the other.

The clogging comes from the cast iron elbow forming scale and plugging the salt water injection site. You cant see anything in the manifold upstream. Never had one of these rust out in the twenty years we used volvo diesels.

 

[dlochner]

The clogging comes from the cast iron elbow forming scale and plugging the salt water injection site. You cant see anything in the manifold upstream. Never had one of these rust out in the twenty years we used volvo diesels.

The other reason for clogged elbow is running at low rpms. Carbon builds up and clogs the elbow. I also suspect the carbon scale retains moisture which contributes to the corrosion.

Diesels want to be run hard and not babied.

 

[Sailm8]

FWIW Another vote for replacement. I bought the whole works because last time I needed a torch to separate the manifold. PITA

 

[Tom J]

Diesels want to be run hard and not babied.

Pulled my elbow off with over 1,000 hours on the engine, just to inspect it. All I found was some soot I could wipe off with my finger.

 

[MikeHoncho]

The kit I bought came with a foil/fiber gasket like you see with auto exhaust manifolds