smokey 1gm10

[kagallag]

my 5 yr old 1gm10 turns the exhaust water black when engaged in gear above medium revs. Water is clear in neutral and at low revs. Manual not too helpful, any ideas ?? <span style="color:blue"> </span>

[srp]

Black = unburnt fuel. Could be a poly bag round the prop or lots of weed and barnacles on the hull.
That's the good bit, and the most likely problem if it has not done too many hours or been badly abused. Otherwise it could be engine wear - worn piston rings or faulty injector. Do you know the engine history?

[penfold]

could be; excessive weed/marine growth on prop and/or hull, bag/rope/other junk on prop, clogged air intake/filter, clogged exhaust/collapsing exhaust hose, knackered injector, knackered injector pump, overpitched/oversize prop. These are approximately listed in ascending order of likely wallet abuse; addressing the cheap ones first is good.

That's not an exhaustive list but enough to be going on with; has the problem manifested itself suddenly, or has it developed gradually?

[andy_wilson]

Black means too much fuel for the available air, hence most diesels blow black when you first open them up, until the revs rise to pump suficient volume of air into the cylinders.

The black is carbon particles not fully converted to CO2 due to insufficient oxygen.

SO

It could be that the air intake has become clogged, easy test, take the filter off temporarilyand see if that improves it.

Harder to diagnose would be the possiblility of a delaminated or otherwise constricted exhaust hose or other part of the system affecting breathing.

Overloading is the other distinct possibility, where the engine cannot turn fast enough for the throttle setting. In order of ease to check:
Excessive hull fouling / fouled and hence inefficient propellor / something wrapped round prop or shaft / gearbox fault (the last few might be revealled by trying to hand turn the shaft whilst in neutral).

Unlike other suggestions, this unlikely to be engine wear, unless you are realy seeing blue smoke, which is burning lubricant, accompanied by noted oil consumption. However, this can also relate to excessive light running, and a good long blast at full, or at least over 3/4 rpm will often clear that up.

Rancid smelling grey smoke is unburned diesel, usually due to a poor injector spray pattern.

After considering the above, it begs the question whether this is a new or old problem, as the overloading bit could also be due to wrong gearbox ratio and / or propellor size.

Other far less likely causes could include very poorly adjusted valve clearences, or equally poorly adjusted fuel metering pump.

[RupertW]

I had a similar problem with my 1GM10 last year.

The prop turned out to be completely encrusted with barnacles and weed which is why neutral was fine - at least at first. Because we were on passage we had to use the engine for about 8 hours as the speed slowly dropped to 2 knots even at full throttle. When the engineers got their hands on it they found a faulty injector as well (as a result of????).

[bendyone]

Check the prop ours had the same proplem the prop turned out to be completely encrusted with barnacles!

[oilyrag]

If you are not suffering a lack of performance, merely black exhaust at higher revs, it could well be the exhaust elbow has corroded internally and is allowing seawater to be drawn into the exhaust port. This is a common problem with these engines and failure to check and replace the elbow regularly has led to many an expensive cylinder head failure. The exhaust elbow is actually a service item which Yanmar recommend is replaced every 2 years!

[birdseye]

andy is absolutely right!

the quantity of fuel injected into the engine is governed by the throttle lever. the quantiity of air is a function of engine revs. so if the throttle is full open and something stops the engine getting to full revs, you have unburnt fuel ie soot in the exhaust

things that can stop the revs / air?

blocked air filter
engine in airtight box
too great a prop pitch
prop fouled
hull badly fouled
inlet valve tappet adjustment.

from personal experience I can tell you that a gm engine using lube oil doesnt leave blcak soot on the surface

[kagallag]

thanks. engine has not been abused. The hull is clean. Would water is diesel affect injector enough to damage the actual injector enough to cause the problem ? I have emtied the water trap at weekend to find a fair bit of dirty water aquired in only a few months.

[kagallag]

thanks for reply. the problem has manifested very recently, ie within the past 5 hrs of running.