Different Mixing Elbow Problem

[Neil McDonald]

One year ago I changed the mixing elbow on my Yanmar 3GM30F. I used an after market elbow from the same source as my last one - which had lasted nine seasons, which ain't bad at all. Yesterday I discovered that new cooling problems were due to carbon blockage in the cooling system. However it was not in the mixing elbow as you would expect. Turned out it was in the brass elbow that connects the mixing elbow to the discharge hose. Totally blocked. An easy fix after diagnosis and a quick poke with a screw driver blade. Everything is now fine, but for how long?

I am baffled by the location of the blockage. Any ideas as to the cause? A chorus of "Don't use after market stuff" would not be helpful!

 

[Benny17441]

Now that you have identified the problem and found that the fix was an easy one perhaps it will be just best to wait for the symptoms to redevelop and then again apply the fix. No ideas why there, but seems fruitless to speculate as the options are "clean" or "replace".

 

[Jake N Eggs]

Could be low water flow through the fitting. If the engine runs a lot at low speed the carbon will build up quicker. The water flow is also lower at low engine speed. Maybe check your pump / impeller. Impeller could be good with a deteriorating housing causing inefficiencies in the pump and low water flow.
Just some ideas. Good luck.

 

[Whatfiero1]

You talking about that 1/2" brass elbow where the raw water flows into the mixing elbow. I know mine seemed to clogged all the time too thought because it makes a hard 90o bend so found a brass 45 deg bend.

 

[MitchM]

since the mixing elbow removes a fair amount of heat , when the exhaust mix gets to the brass connector, it's cooler. that may explain why there's more carbon particulate condensing on the brass.... but at lest you don't have to replace the mix el !!

 

[SG]

Do you have a brass or bronze elbow?

 

[Rick D]

I had the same issue on the same engine. I made a point of cleaning it yearly.

 

[Neil McDonald]

Thanks for the interesting feedback. Yes the engine has been run at low speed. Over the winter I periodically, every month or so, idle the engine at low speeds for maybe 15 mins at the dock. Maybe this caused the problem. As part of my diagnostic procedure I connected an external hose to the hose removed from the brass elbow to discharge water overboard with the engine running. Not exactly a firefighting flow resulted but it still looked healthy. With the blockage removed the exhaust sound has returned to the historic and comforting "splushing" sound. Engine didn't actually overheat, I just knew from the exhaust sound that cooling water was not there. I'm comforted that others have had the same problem and it's certainly easy annual preventative maintenance!

 

[SG]

The engine is not likely to overheat with unacceptable flows at an idle speed. It's a moderate to higher load and RPM's that the engine would show heat build-up.

 

[RajinCajun]

As a rule before engine shutdown, I run the RPM's up to clear engine, return to idle and kill engine immediately.

 

[markwbird]

It's the narrowest part. I have the same engine, same problem. Just clean it regularly.

 

[Neil McDonald]

Don't want to beat this topic to death but surprised that I've run this boat for 13 years without previously having had this problem. Looking at cut away sections of failed mixing elbows I see two parallel internal passages, water and gas, that converge maybe six inches away from the initial water inlet. This junction is where I would expect maximum carbon build up. I wonder if my after market elbow casting has a flaw which allows gas to meet water very close to or even at the initial water inlet? No way of knowing!

 

[SG]

If it's a brass fitting, and not bronze....

 

[Neil McDonald]

Yes SG its brass not bronze ..........?

 

[SG]

That's can crude-up more easily, won't hold-up as long, and you need to be more careful when you clean-it, Neil.

 

[John Nantz]

That was a good thread, Neil. Noticed some carbon build-up in the little brass or bronze elbow that would probably reduce the amount of water flow to the mixing elbow. Never bothered to check it between mixing elbow changes because it was never a full blockage but will start doing it now. Your description of the way the water comes out with a "splushing" sound when everything is working properly really describes it well.

 

[Neil McDonald]

Two or three times over the winter I used to run the engine at idle for maybe ten minutes. Won't do this anymore! Marina regs don't allow tying off to the dock and running under load. Some people say leave engine alone over winter if you can't run it under load.