Yanmar exhaust mixing elbow-service

[Endurance2010]

Skippers:

I recently traced a raw water failure to my exhaust mixing elbow. Apparently there was quite a bit of black soot in the 90 degree fitting from the raw water line from the back of my heat-exchanger to where it enters the elbow. I spoke with a neighbor and he said he changes his exhaust elbows every 5 years. I spoke with my local Yanmar parts dealer and she said she sells quite a few replacements every year in the Bay Area. The cowling below my elbow is also quite rusted.

Query: does everyone commonly replace their mixing elbow and cowling every 10 years or 500 hours or so? My manual is silent on this. I cleared out the problem, am I good to go until it fouls up again? I'm leaning toward replacing this in the summer. What do you think? Thanks.

--Dan

 

[Steve Dion]

Dan:

When you are in salt water these units corrode out much quicker than in fresh water. I think you would be wise changing out the unit and then determine if the old one is any good.

I think many owners need to replace theirs every 5-6 years. I also think if you run your engine at higher RPM's it keeps the elbow cleared out and there is less coking.

Obviously you got the units apart, which is normally a SOB. If the manifold is in good condition there is no reason to replace it.

When you take them apart and re-assemble you should always use never-seize on all of the threads.

 

[John Nantz]

Less than 10 years, basically

I'd say the cleaning and replacement frequency would depend on a few factors, like the RPM the engine is run at, how many hours at those RPMs, and probably how good the injectors are and the timing, etc.).

With regard to motoring on our 3GM30 fresh water cooled engine, it is recommended to run the engine at 80% power which is around 2880 RPM. I'm usually a tad under that at around 2750 because that seems the smoothest. I don't get any appreciable soot buildup on the transom, either.

If one is on the hook, say, and runs the engine to charge the batteries, the RPM I see most people run at is a slow to medium idle which I don't think the Yanmar reps would approve. Could be wrong, but that's less than the recommended working load.

As for frequency, I couldn't give a real time period but for the way we use the boat (and engine) we're cleaning our elbow every couple years and replacing it when it needs to be cleaned again.

The problem with not replacing it is, especially in salt water, it will rust out and at some point the exhaust will leak out through a crack and then a hole. Not desirable.

And the experience of getting the coupling off is, well, a royal pain. Guess you've already been through that, though.

 

[seadaddler]

Mixing Elbo

I did clean the mixing elbo once and since it went so well I would clean it again every other year and so did not need to replace it.
Nick

 

[zeehag]

the 5 yr thing is from th edistributor. i was advised about thi8s when i got my ericson 35mII and had the yannie overhauled-- before overhaul. she blew black smoke and didnt put out. after the overhaul, i have a brand new engine... new elbow and all-- that was 6 yrs agoi havent used her much--less than 150 hours nd is still ok. i am anticipating the replacement-- my former sail partner has a 3gm and took his mixing elbow off and cleaned it-- is still good, as far as i know. that was last summer.

 

[Mike H.]

The system seems to be the same concept on gas and diesel engines.

I had a 82 Searay SR1, (sweet boat), and it had low power and overheated all the time.

I took it to the shop and they said "We'll look into it and call you". About two weeks latter I called and they said, "It's almost finished, we rebuilt the top end". Well, thanks for letting me *%#*&!% know!

$ 2,000. latter, they had removed the heat exchanger, changed the elbows and rebuilt the heads. It turns out the PO had run it in salt water and didn't flush the system, the elbows corroded the water passages closed, the heads overheated and burned the valves. I was a lake boater at the time, so I didn't need the heat exchanger.

So yeah, the elbows need to be maintained. That's your passage way for cooling water.

 

[Alan]

Just replaced mine (3GM30F) after 17 years of loyal service. A telltale rust streak on the exhaust hose proved to be the last this elbow had to give. Flushing with fresh water after each use would prolong its life but with 17 years on the first one it hardly seems worth the effort.

To all you DIYers I highly recommend removing the mounting bolts one at a time and coating them with a high temp anti-seize compound at your earliest convenience to make the next time easier. All going well this job takes about an hour to change out the elbow.

 

[Brad Hoff]

I have cleaned mine twice now. Lasted about 5 years after cleaning. I soak it in muriatic acid overnight. Cleans out all of the coke down to the shiny metal with no other scraping involved.