Yanmar 3GM30 - how much smoke is OK?

[akio.kanemoto]

Greetings Folks,

Something I've just noticed (maybe it's been doing it for a while?) - is that my engine makes a bit of smoke while running under load.

Right now for example, I'm running at 2000rpm and charging my batteries and there is a grey'ish smoke coming out.

Normally I don't notice this as it dissipates, but today there is no wind at all.

To give an idea, there is perhaps only 3-5kn of wind the this light grey'ish smoke completely disappears about 3ft (1m) back from the exhaust outlet.

Is it supposed to be zero smoke or is this normal?

Thank you!

[roverhi]

Don't know whether it's normal or not but my 3GM puts out a noticable amount of smoke when running what I'd consider normally at cruising speed. It's not a heavy fog but you can definitely tell the engine is on. If there is something wrong like it's overpropped or there is a fuel delivery problem, dtdt, then it's put out a cloud that very definitely got my attention.

Sounds like yours is normal but might want to see what other's experience has been.

[delmarrey]

How many hours on the motor?

It could be one or more of many symptoms, could it be steam. Is it leaving a oil slick on the water.

[akio.kanemoto]

Originally Posted by delmarrey

How many hours on the motor?

Thanks for the quick replies!

It could be one or more of many symptoms, could it be steam. Is it leaving a oil slick on the water.

Officially 121 hours on the clock - but I know that it's been rebuilt/refurbished or somesuch - it came with the boat.

My exhaust run is quite long and so the water at the outlet is quite warm as I believe the exhaust gas and water travel together quite a bit and the heat is transferred. The mixing elbow directly after the injection point is cool to the touch.

There is no oil on the water at all.

[akio.kanemoto]

As an addendum btw, I am currently charging, not underway (underway, the smoke can't easily be seen as the wind blows it away). I have a pair of 120A alternators balanced on a special mount etc so no side loading, and I start charging at 2500rpm, putting out about 220A, then throttle back to about 2000rpm as the output drops. Right now after about an hour, I'm down to about 70A output.

There is no difference in smoke output based on rpm.

[delmarrey]

Without actually being there, it's a hard guess. It could be nothing as roverhi stated. Being a new boat to you I'd just run it awhile and see if there are any changes. Black smoke usually indicates an over load on the motor. Whitish/gray is too much fuel, sometimes or air flow restrictions.

[akio.kanemoto]

Also, I've just removed the oil filler cap at the top and had a look, there is no smoke coming out at all (I don't know what this is supposed to be checking, but I found somebody else referring to this as a check!)

One last thing - my IR gun pointed at the engine block (just next to the anode on the side) shows that the temp as 68degC (154degF).

[delmarrey]

Originally Posted by akio.kanemoto

As an addendum btw, I am currently charging, not underway (underway, the smoke can't easily be seen as the wind blows it away). I have a pair of 120A alternators balanced on a special mount etc so no side loading, and I start charging at 2500rpm, putting out about 220A, then throttle back to about 2000rpm as the output drops. Right now after about an hour, I'm down to about 70A output.

There is no difference in smoke output based on rpm.

Diesel are best run under load! Otherwise the cylinders become polished and starts a compression loss.

It is better to take the boat out on the water to charge batteries. Or tie the boat to the dock and run at a mid range. The prop will cavitate if run too hard at the dock.

[delmarrey]

Originally Posted by akio.kanemoto

Also, I've just removed the oil filler cap at the top and had a look, there is no smoke coming out at all (I don't know what this is supposed to be checking, but I found somebody else referring to this as a check!)

One last thing - my IR gun pointed at the engine block (just next to the anode on the side) shows that the temp as 68degC (154degF).

All good!
Pulling the filler cap would show if you have blow-by. If so then that would indicate cylinder compression passing the piston rings.
A fresh water cooled motor, on the gauges, should run between 160º & 200º F depending on the load.

[akio.kanemoto]

Originally Posted by delmarrey

All good!
Pulling the filler cap would show if you have blow-by. If so then that would indicate cylinder compression passing the piston rings.
A fresh water cooled motor should run between 160º & 200º F depending on the load.

Mine is raw water cooled, so this is OK?

[akio.kanemoto]

Originally Posted by delmarrey

Diesel are best run under load! Otherwise the cylinders become polished and starts a compression loss.

It is better to take the boat out on the water to charge batteries. Or tie the boat to the dock and run at a mid range. The prop will cavitate if run too hard at the dock.

OK, this is the challenging bit - basically with the two 120A alternators, the engine can't support propulsion AND charging simultaneously unless I derate the alternators by using the "Limit" setting on the alternator regulator (SARV3) and cut output by about half. (and I'm pretty sure my prop pitch is a little too much... and I will change the settings as soon as the weather clears up)

So based on that, I was thinking that the alternator load is enough to give the engine "enough" load? Or does it really need the load from the prop?

[delmarrey]

Originally Posted by akio.kanemoto

Mine is raw water cooled, so this is OK?

In colder climates, probably yes. But then it comes down to your thermostat. Raw water cooled can vary.

[delmarrey]

Originally Posted by akio.kanemoto

OK, this is the challenging bit - basically with the two 120A alternators, the engine can't support propulsion AND charging simultaneously unless I derate the alternators by using the "Limit" setting on the alternator regulator (SARV3) and cut output by about half. (and I'm pretty sure my prop pitch is a little too much... and I will change the settings as soon as the weather clears up)

So based on that, I was thinking that the alternator load is enough to give the engine "enough" load? Or does it really need the load from the prop?

If your alts are loading the motor? Fine! If the charging amps start to get low an increase in RPM's would keep the cylinders under more load. Idling a diesel for long periods is the killer.

[akio.kanemoto]

Originally Posted by delmarrey

If your alts are loading the motor? Fine! If the charging amps start to get low an increase in RPM's would keep the cylinders under more load. Idling a diesel for long periods is the killer.

There's definitely some load - I generally stop charging once the load from the amps gets below 60A or so.. and I never take the revs below about 1800rpm while charging. I start at around 2300-2500rpm (below that the alternator output stalls the engine and you can really hear it suffering) and then taper rpm down to 1800 or so.

Oh, and I make water at the same time as well - so there should be about 5HP load on the engine minimum.

I've also read somewhere that prior to shutdown, you remove all load, then crank it slowly up to near max rpm (3500 or so) and run for 20 seconds, to blow out carbon, then slowly drop it back to idle, let run for another minute, then finally stop the engine.

I've been doing this as well - is this correct?

Thanks again!

[delmarrey]

Originally Posted by akio.kanemoto

There's definitely some load - I generally stop charging once the load from the amps gets below 60A or so.. and I never take the revs below about 1800rpm while charging. I start at around 2300-2500rpm (below that the alternator output stalls the engine and you can really hear it suffering) and then taper rpm down to 1800 or so.

Oh, and I make water at the same time as well - so there should be about 5HP load on the engine minimum.

I've also read somewhere that prior to shutdown, you remove all load, then crank it slowly up to near max rpm (3500 or so) and run for 20 seconds, to blow out carbon, then slowly drop it back to idle, let run for another minute, then finally stop the engine.

I've been doing this as well - is this correct?

Thanks again!

The Yanmar 3JH manual recommends that the motor needs a cool down period. Also just before shut down that one rev's it 4-5 times (but not hold it at hi rpm's) before shut down to blow carbon out of the system.
I'd check your manual to be sure.