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vanderd · 03-07-2021, 16:42

I have a 2006 44 foot trawlercat. It’s powered with two Yanmar 4LHA - STP engines. I changed the mixing valves seven years ago and I’m wondering if it’s time to do so again. Somewhere I had heard to change them every five years but I’m not sure if that’s a reasonable timeframe. Also any thoughts on the OEM part verses aftermarket stainless steel? I remember having a very difficult time fully inserting it into the exhaust hose. While I didn’t damage the wet muffler with all my pushing and twisting, I certainly was concerned. Any tips to ease installation

ilenart · 03-07-2021, 23:55

When I purchased my HR 40 in 2019 it was obvious the elbow had’nt been replaced in +10 years, which meant the exhaust elbow and heat exchanger had to be replaced, which was a $10,000 job. The surveyor’s report (who is also a mechanic) under Engine Maintenance Guidelines” includes “replace or check exhaust elbow every 4 years”. Will be following his advice.

Ilenart

**Dockhead** · 04-07-2021, 01:13

$10, 000 for exhaust elbow and heatex? I'm in the wrong business. And what does the heatex have to do with the exhaust elbow?

Life of the exhaust elbow depends on the construction of it, and qualities of the water put through it, and engine hours. Rather than replace it on a schedule, carry a spare, and inspect it regularly. Cleaning it is a good idea if carbon tends to build up in it. I got 20 years and 15,000 hours out of the exhaust elbow on my previous boat. I replaced the one in this boat at 16 years and 3000 engine hours, because of a pinhole leak. The new one cost £300 to fabricate and less than an hour of my own time to install.

ilenart · 04-07-2021, 02:13

Quote:

Originally Posted by Dockhead

$10, 000 for exhaust elbow and heatex? I'm in the wrong business. And what does the heatex have to do with the exhaust elbow? .

I’m talking Oz dollars and the exhaust elbow was connected to the heat exchanger on the top of the engine and the corrosion had worked its way back through the exhaust elbow. Not a big issue for me as the cost was knocked off the purchase price in the final negotiations.

vanderd · 04-07-2021, 10:21

I am all for not changing Exhaust Elbows if tey don’t need replacing. How do you know when they go bad? I had heard that raw water can get into the engine and do a lot of damage. The Turbo is immediately in front of the elbow I would hate to see seawater attack it.

Sailnav · 04-07-2021, 11:02

The mixing elbow on my 3-cylinder Perkins is a nicely solid iron casting, and at 2,000 engine hours it looked brand new.

But hot gases and salt water turned the interior into rust, and the buildup caused the 2-in.-dia orifice to shrink to a pinhole, choking the engine.

Diagnosing the performance drop-off was a nightmare. Lesson: remove the mixing elbow periodically and inspect the interior.

Manateeman · 04-07-2021, 12:50

We posted a reply to a similar OP question. Our engine is a Yanmar 4LH turbo aftercooled 170 hp. We changed to a stainless mixing elbow early on.
We designed an exhaust gas/ water separator to minimize back pressure on the turbo. We took the new turbo ...first one rusted ...to a professional CeraKote applicator who coated the exterior and the INTERIOR of the HOT side. We checked with the turbo maker and there was more than enough fan tip clearance.
Or Northern Lights genset came with a cast elbow which we changed to Stainless.
We are now adding a raw water flow alarm.
D’Angelo Marine Exhaust in Ft. Lauderdale. Experts...period.
I wish any forum members could invent an oil flow alarm for the turbo and another for our transmission cooler.
Happy trails to you.

Captain Mark and his manatee crew using turbo waste heat in the fermentation tank part of their onboard micro brewery.

Who has a crew like this!

Squanderbucks · 04-07-2021, 15:13

This another one of those examples about when to do “preventive maintenance” ie before the fact or after the fact.
With most things there are rules of thumb or suggestions that have been gleaned from either experience or engineering suggestions. A lot depends on how critical the result of waiting too long. Oil change? 100 hrs, 200 hrs, 1 yr etc.
with exhaust elbows it also is dependent on where they were made. Chinese manifolds and risers will last from my experience and those of the engine repair guys I know about 1/2 to 2/3 as long as domestic or European made. Their iro and aluminum castings are “junk” as far as a starting material and must be taken into account.
By definition. Preventive means replace it before failure. Risers in salt water with little use will crap out faster because the culprit here is the salt and Oxygen. A riser run in salt water every day will last longer than one run a few times a year and set with no flushing.
Another subject to be considered is is the engine flushed with fresh water upon return from use and allowed to set.
It’s the oxygen baby.

thunderhoof · 04-07-2021, 15:42

After dealing with a mess of a corroded thru Al mixing elbow and damaged Al exhaust manifold on my VolvoPenta MD3020 I replaced the mixing elbow with a stainless steel item from HDI Marine. It fit perfectly. I think everyone should do this because the combination of hot salt water and hot exhaust gas under pressure is not the place for an Al casting. (Cheaper than the V-P part too.)

EmeraldCoastSailor · 04-07-2021, 16:59

I replace mine every 5 years. Easy enough job and based on my understanding of the construction of the elbow, a leak in the wrong place could damage engine badly. The one elbow that went bad on me leaked externally which made it easy to diagnose; it leaked on electrical connections that wasn't great but was easily fixed. Maybe they always leak externally? But if it leaked internally it would be bad. The three that have been on my 3ym30 have been ss.

kapnd · 04-07-2021, 17:14

Squanderbucks nails it at the end of post #8.
Standing salt water in any metal container is a bad idea.
A few moments effort put into flushing the motor after operating are prudent.