Smoky Yanmar 3GMD

[frankv1205]

Have a white smoke issue with my Yanmar 3GMD for over a year now . This year engine didn't start so an electrical fuel pump was installed which corrected the start issue also had the fuel injectors replaced and valves adjusted also had the exhaust elbow checked and it was fine, but I was still having the smoke issue. I was told maybe I had to much additive in fuel so I replaced the fuel with all clean fuel.The engine starts right up and I can get 3400 RPM with no load and 2600 RPM doing 6 Kts when cruising with no issues. Mechanic says it runs like an old engine and unless I want him to tear it down he doesn't know what else to do. I'm thinking that since the engine is running fine it could be something simpler that I should consider before the expense of a rebuild. Hoping someone here could give me some ideas I could check?.....Thanks!

[a64pilot]

Explain white smoke, does it have a smell? Does it rapidly dissipate or does it stay and drift away? Does it start immediately and go away when engine is hot, or does it not appear until engine is under a load?

What RPM do you get when it's at full throttle and in gear in forward?

[sailorchic34]

White smoke is water, Grey smoke is unburnt fuel and blue smoke is oil.

Is this a raw water cooled engine or fresh water cooled.

I assume raw water cooled. If it's raw water cooled, I suspect you have some minerial buildup in the water jacket. This lets the water get hotter which causes the white smoke. If that is the case, you might want to do a jacket flush with a pump, bucket and diluted Muriatic acid or better yet phosphoric acid. This removes the mineral buildup in the water jacket and lets the water conduct more heat away.

[frankv1205]

White smoke is definitely exhaust it does have an smell and does hang around the boat and I do get all the time seems a little less when cruising
Yes this is raw water cooled and my temperature gauge never gets above 100 but I did have the thermostat replaced also and it did'nt make a difference

[a64pilot]

If it stinks and hangs around, it's not water vapor, most likely fuel.
For fuel I suspect injectors first, then valves and engine compression last.
Does the engine idle smooth? Do you know how to loosen the fuel injector lines one at a time, listening for the cylinder to cut out?

How much oil does the engine consume, a quart every how many hours?

[frankv1205]

At full throttle it is running at 2600 RPM I forgot to mention I do get a small amount of sheen from the exhaust which i assume is unburnt fuel

[sailorchic34]

Is the discharge water temp hot. That is can you hold the hose that connects to the discharge elbow with the engine running. A 100 degrees F would be just slightly warm, 120F would be almost too hot to hold.

Oil sheen, odds are is a bit of unburt fuel which could be a bad injector, clogged/carboned precombustion chamber Injector timing off a tad (rare).

If it starts easy and runs well, which it does, I would agree with the mechanic. Lots of old Yanmars do tend to smoke a tad.

[a64pilot]

Originally Posted by frankv1205

At full throttle it is running at 2600 RPM I forgot to mention I do get a small amount of sheen from the exhaust which i assume is unburnt fuel

OK, your 1,000 RPM down from max, meaning that your either over propped, or way down on HP.
You can live with being over propped, just use your brain and don't over strain her. Maybe cruise at 2000 RPM and not much more.

I would start by having it warmed up, and put it at an idle speed where it's smooth, the lowest smooth speed. Then one at a time loosen the injector nut til fuel starts spurting out and listen for engine speed to drop and it should start to shake, tighten nut, go to next injector.
If you find one that doesn't get rough and drop RPM, you have a problem cylinder. They should all be the same
Do check your water temp at the exhaust, but check it after its been under a load, let it get a chance to get hot if its going to.

[frankv1205]

Im burning no oil and never have to add oil during season
Would a compression check be the next thing I should have done?

[sailorchic34]

If it starts easy, compression is fine. The first sign of low compression is hard starting.

[a64pilot]

Originally Posted by sailorchic34

If it starts easy, compression is fine. The first sign of low compression is hard starting.

From a general wear perspective I'd agree, but it is possible for one cylinder due to a busted piston or a mal adjusted or bent or burnt valve to be down on compression.
I think though that doing the loosen the nut on each injector will tell if you have a weak cylinder through.
I suspect a bad injector, pretty strongly suspect that. Bet money on it in fact.


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