Almost didn't do a stupid thing

[arf145]

But not quite. Back in the winter I planned to inspect the mixing elbow on our Yanmar 2GM20F because I had no idea how old it was and suspected it was an original 23-yr-old part. I was mainly concerned with carbon buildup. But I had so many demanding projects and the damn thing looked shiny enough, and I could picture struggling to unscrew that big coupling and hurting myself in new and exciting ways, so it didn't get done.

Friday we were motoring out about a mile from the marina when I heard the engine suddenly sound different, and then saw no water coming out the exhaust. I cut the engine and we put up the main to have some control while I looked things over. I figured we had sucked a plastic bag into the intake.

Nope, nothing blocking the water. Instead, the mixing elbow had broken off at the engine exhaust side completely! Cooling water was spurting back into the bilge and exhaust was venting into the engine compartment. I had no temporary fix for this, so we were towed back to the marina.

Inspection showed the break was in the threaded coupling between the engine and the elbow. The threads were actually eaten through in spots other than the break, which makes me think it might have been leaking some exhaust for a while. Yikes!

The elbow itself was carboned up pretty bad so I replaced the coupling and the elbow. I imagine if I had tried to remove the elbow back in the winter, that coupling would have ripped right off at a more convenient time. Oh well. It actually could have happened at many much more inconvenient times and places, so I lucked out in the end.

[bljones]

On the upside:
1. You found the problem and have a plan to get it solved.
2. It has been leaking for a while and you haven't died.
3. You learned a lesson- if you THINK an part should be fixed/ replaced, the fix/replace it, otherwise it will bite you in the hiney at some point in the future.

[jarcher]

I have the same engine, and had a lot of trouble with it a few weeks ago. Air was getting into the fuel line. I think I'll check the exhaust for the problem you had. Thanks for posting this!

[FarCry]

I have an even older QM15. As a proud male I ignored my spouse's comments about the smell of exhaust in the cabin telling her it was just some residual coming in since we were motoring with a light wind astern. It turned out to be a small crack on a shiny pristine looking mixing elbow of unknown age. After conferring with all the local "experts" while consuming some adult beverages, it was agreed upon by all that the thing to do was to remove the four bolts holding the flange onto the block and not attempt to unscrew the elbow from the flange. Then the option was to put the flange in a large vice, spray it with PB Blaster over the course of a few days, beat it with a hammer, heat it with a torch, crank on it with the largest pipe wrench available and then....just go ahead and buy a new elbow and flange because the two pieces will nearly be welded together. Being frugal but not totally stupid, I took out the four flange bolts and connected hosing in less than an hour and tried for a day or so to break the elbow free with no success. Given more time I am sure it could be done but it seemed like a poor way to spend my time with a very real chance of damaging either the flat flange mating surface or the machined threads that the elbow attaches to.

The carbon buildup on my old elbow didn't seem that bad. Scraping some off it appeared to only be about 1/4" thick at most.

[P35juniper]

I had to clear carbon out of my 3GM30F mixer elbow, the riser pipe from the flange to the elbow is threaded right-hand on the flange and left-hand on the elbow.

[arf145]

FarCry, I guess I was lucky that I actually got that coupling off then--and I did it in place! And didn't hurt myself while pushing with all my strength! A miracle no doubt--and a testimony for PB Blaster. It didn't even occur to me take off the manifold. Yet I did dismantle a good bit of the cabinetry around the engine. Probaby why I escaped with no injuries

P35, the guy that sold me the parts was kind enough to show me how the threads on the two ends were opposite, so I wouldn't spend all day trying to get the threads to start in the wrong direction. I had to admire how shrewdly he sized up who he was dealing with there

Tom