Yanmar 3ym30 big smoke at revs

[Al.]

Houston I have a problem. I have a Yanmar 3ym30 with 300 hours on the clock. Has been flawless until now. Runs sweet up to 3000 if slowly increasing the RPM then blows smoke big time and I can see the unburnt fuel on the water. Snap the throttle open and it blows smoke at 2500RPM. The engine develops a rattle when this is happening also. The engine has been run in correctly with regular short bursts at full throttle. This is with no load as well. Can anybody shed some light as to what the problem might be? Cheers.

[shakey doug]

G'day Al,
Sounds typical of a blockage on the exhaust side of things.There are a number of cause to this problem but the rattle gives it away, please post your findings.

Cheers, Shakey.

[Chief Engineer]

I would look at the injectors first

[Al.]

Shakey. On the money. We found carbon build up in the mixing chamber and now revs to almost 4000 and no smoke. I am supprised how 50rpm made the difference between no smoke and plumes of it. The service manual says to check the mixing chamber every year but at 300 hours I thought it would be fine. Thankfully one of the first two things we checked , the intake and then the exhaust solved the problem Cheers All. Good Forum

[gjordan]

QUESTION? Why is it some marine diesels seem to go several thousand hours without exhaust manifold (mixers) problems and some clog up regularly? Is this inherant in Yanmars or do other diesels do this. I think my Perkins 4-154 had something around 3000 hrs on it when I sold it , and had no exhaust problems. Many other little problems but not exhaust?____Grant.

[Ex-Calif]

Can be related to the exhaust system design or more likely the fact that many owners run their diesels too much with insufficient loads.

[delmarrey]

Originally Posted by gjordan

QUESTION? Why is it some marine diesels seem to go several thousand hours without exhaust manifold (mixers) problems and some clog up regularly? Is this inherant in Yanmars or do other diesels do this. I think my Perkins 4-154 had something around 3000 hrs on it when I sold it , and had no exhaust problems. Many other little problems but not exhaust?____Grant.

One has to reduce back pressure as much as possible. Unless they have a turbo, then it has to be set up to a certain spec. (done with gauges).

If ones exhaust exit is at the waterline, the outlet can dip below the waterline under certain situations. Or the amount of lift in the exhaust loop.
Also the design of the elbow can make a difference. There are many variables.

[Capn Morgan]

We recently changed the mixing chamber as it had corroded through on the side. Inside it, there was a large buildup of carbon deposits that refused to come out even at full power. It got hard and didn't want to shift or even burn.

Diesels evidently don't thank you for treating them kindly... we've been told to run it well above the point where the turbo kicks in (4LH TE). Problem is, at that stage it is when the boat is approaching hull speed and the law of diminishing returns!

[roverhi]

Make sure your fuel filter isn't clogged.

[Samantha ann]

Is your prop clean?