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copacabana 12-05-2013 05:34 AM

Clogged Yanmar mixing elbow?
I have a Yanmar 3GM30F engine with 2,500 hours on it. It starts cold on the first crank and runs like a champ, but I have noticed that recently I can't get it to run at revs higher than 2,700 RPM. I have started eliminating possible problems (air filter, fuel filters) and now I will try replacing the mixing elbow. The model of mixing elbow is this one:

Yanmar Mixing Elbow 128370 13550 FOR 3GM30 | eBay

I know that mixing elbows can slowly get clogged with carbon buildup, especially the "U"-shaped ones, and restrict exhaust outflow, preventing the engine from getting up to full revs. The model of mixing elbow I have is a gentle angle (45%?) with a welded pipe on top for the cooling water to enter the exhaust. It doesn't seem that carbon would have a chance to build up in this elbow. Is that the case? I want to change it anyway as the welds are getting rusty and I know it's on its last legs (it's the original one that came with the engine).

Has anyone had carbon buildup problems with this model of mixing elbow?

jsaronson 12-05-2013 06:14 AM

Re: Clogged Yanmar mixing elbow?
remove the water hose that feeds the elbow. I bet it is blocked.

copacabana 12-05-2013 09:15 AM

Re: Clogged Yanmar mixing elbow?
JSaronson, have you got the same engine and mixing elbow? I'm loath to remove it before I have the new part (and gaskets) to replace it. I will certainly check for carbon buildup when it's off.

Faster 12-05-2013 09:25 AM

Re: Clogged Yanmar mixing elbow?
Mark.. I'm guessing it has little to do with shape.. the hot gases hitting the colder water probably precipitates material over time in any case.. (but just guessing ;))

copacabana 12-05-2013 09:38 AM

Re: Clogged Yanmar mixing elbow?
Thanks Ron. I'm rather hoping to find the elbow clogged with carbon. Then I'll know I've found the problem. I'll find out when it's off. I know the U-shaped Yanmar elbow is prone to buildup, but the one I have just seems to have such a straight run that I can't see how it gets clogged. If anyone has the same elbow, I'd love to hear about clogging.

jsaronson 12-05-2013 11:08 AM

Re: Clogged Yanmar mixing elbow?
I have the U shaped elbow with a straight pipe for the water inlet. The inlet was completely blocked.

christian.hess 12-05-2013 11:19 AM

Re: Clogged Yanmar mixing elbow?
soak in vinegar and do some vingear flushes of the intake and let it sit for a while

does wonders

edit I had the 2gmf, I think the elbows are the same...not sure though:)

Melrna 12-05-2013 11:21 AM

Re: Clogged Yanmar mixing elbow?
I had it in my old boat. Yanmar recommends changing it out every 250 hours or get it cleaned at a radiator shop. The mixing elbow in this model is very prone to carbon blockage. Also the water inlet to the mixing elbow is famous for getting clogged first.
One way to know is the exhaust smoke starts to get white at running speeds.

christian.hess 12-05-2013 11:25 AM

Re: Clogged Yanmar mixing elbow?
before removing put the inlet in a vinegar bucket...start engine and completely suck all the vinegar till it starts coming out...

let sit for at least 24 hours...sometimes up to 48

then flush with distilled water(cold)

if this DOESNT help you must dismantle and manually clean

this shoud be done as regular maintenance and you save a lot of money versus buying industrial engine "cleaners"

I did this on my last engine an atomic 4 and the difference in max loaded rpm was very noticeable

power loss and parasitic loads can come from many sources on an engine, fuel, air, cooling system, belt chafe...etc...

miatapaul 12-05-2013 11:29 AM

Re: Clogged Yanmar mixing elbow?
Seems cleaning would be a lot cheaper than replacing. I would pull it and if you see any carbon on it, take to a radiator shop and ask them to "boil it out." (not sure what the Portuguese term would be as they don't really boil it) They generally have baths of really strong chemicals that they can dip it into and it will clean it to bare metal. You should be good to go for several more years after that.

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