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Old 26-05-2008, 09:58   #1
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Gm30 Brown slick from exhaust

Hi All newby here looking for some help.

I have tried searching the wealth of information in these forum's but have not found the solution.


I have a Benetau Oceanis 321 in Turkey and recently started experiencing problems.

To start

Last October, we suffered water contamination of our diesel tank, that we drained and replaced with fresh diesel.

This season first time out at 2500 - 3200 rpm (max available) exhaust is producing brown smoke and slick (smoke was not so bad at first but getting worst)

Engine has started no problem after 6 months, running at upto 4000 rpm - (no load) no problem experienced.

Prop has been examined and is not fouled.

Water flowing from exahaust and engine temp OK.

Had fully serviced last year with all new filters.

Does not appear to be using any oil and oil seems clean.

Hopefully someone can point in right direction
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Old 27-05-2008, 12:13   #2
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Have your injectors pulled and tested, possible water damage to the injectors.
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Old 27-05-2008, 13:43   #3
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Is this a Turbocharged motor? A failed Turbo can cause what you are describing.
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Old 03-06-2008, 05:03   #4
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Hi Thanks for the replies.

I have removed injectiors, whilst no obvious signs of damage have been unable to get checked.

It would seem what i have descibed as brown smoke / sludge is in fact black (light playing tricks) whilst trialing after doing further checked we recoved some of the "sluge" emitted from the exhaust and appears to be carbon / soot.

Whilst checking the air filter which was supposed to have been replaced on last years service, it seems to have been burnt or not replaced for some years and degraded / burnt. Concerned part of filter could be in air inlet manifold and decreasing air input.

Running with no air filter did not change amount of smoke in fact seems to be getting worst.

It would seem engine is carboned up, have tried to check the mixing elbow on the 3gm30 but can not see how it come off.

Any advice, on how to determine if black smoke is lack of air or too much fuel?

Although some weed is on the boat it is not as bad as when purchased so don't feel its down to this.

Does it pay to try and run engine hard to remove and try to clear?

Have attached pictures.

Thanks for your help
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Old 03-06-2008, 05:04   #5
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Sorry should of added, its a 3gm30 which is not turbo charged
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Old 03-06-2008, 05:12   #6
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sounds like your prop is over pitched or too big and engine if working too hard. how high can you get the rpm's when in gear?
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Old 03-06-2008, 05:36   #7
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sounds like your prop is over pitched or too big and engine if working too hard. how high can you get the rpm's when in gear?
It was the engine and prop set up from Benetau and was not a problem last year, even with more weed on.

What's strange, can run engine in marina up to 4000rpm even in reverse whilst tied up to put under load (although prop may be cavitating) without any smoke or soot discharge.

Under normal motoring load conditions max rpm approx 2800- 3000 rpm when problem starts.
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Old 03-06-2008, 06:04   #8
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Your pictures say a thousand words. for what ever reason, you have engine versus load problems. Try taking the load off and running the engine .(wack it in neutral) I am sure that you will see as the engine builds up revs that the"smoke " will clear. All of the above advice may be the problem. At the worst it may even be shaft binding (unlikely) In reverse the load on a lot of props is way less so may not show the symptoms. To much fuel is a product of to much load. This may be because your engine is stuffed ! The injectors or pump are the same.....the prop (or your hull ) is fouled....there is friction in the drive train (have you free wheeled the gear box by hand) If I am right it will happen more at low revs ...call it a chug...the engine is reluctant to come up to full....(at the full range of the govener) . I (being a poor bugger) have lived a life with old diesels. The beauty of them is that you can eliminate the problems one by one.

1. prop....no foul...no damage
2. shaft...easy turn
3. boat...no excess crap
4. gearbox can you turn it by hand.
5. Its your engine !! START AGAIN


1. check your fuel...clean and no sludge...how old
2. check your filters air and fuel.
3. does it start easily IN COLD WEATHER
4. when it starts does it blow smoke on start up , and for how long
5. well there is no 5 ...you are down to engine stuff...

Raw water cooled ? you may have rusted a valve....or a million other possibility's. sorry...
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Old 03-06-2008, 07:49   #9
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1. prop....no foul...no damage - Checked no fouling
2. shaft...easy turn - will try
3. boat...no excess crap - has weed growth, but not as bad as last year with no problem
4. gearbox can you turn it by hand. -will try
5. Its your engine !! START AGAIN - oh no !!


1. check your fuel...clean and no sludge...how old - had problem with sludge end last year, replaced with fresh
2. check your filters air and fuel. - major issue with air filter seems to have burnt away? now replaced
3. does it start easily IN COLD WEATHER - don't know, never in Turkey when its cold (live in UK), came back after 6 months and started first time.
4. when it starts does it blow smoke on start up , and for how long - when it starts there is no smoke.
5. well there is no 5 ...you are down to engine stuff...

Raw water cooled ? you may have rusted a valve....or a million other possibility's. sorry...
Thanks for your reply
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Old 03-06-2008, 09:00   #10
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definitely too much load, hey Cooper keep your advice about others advice to yourself...we all speak from experience, at least I do, and will give advice when I know what I am talking about. Sounds exaclty like what happened to me with a previous boat of mine...could not get rpms up without black smoke, I reduced pitch on prop and changed the oil....solved my problem. The rest of your advice is good and should always be checked as routine maintenance regardless of whether one has a problem.
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Old 04-06-2008, 02:31   #11
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George, you misunderstood Cooper. He is said " All of the above advice may be the problem". It means all suggestions above are possible faults. It is the way we speak down here on the underneath.
Problem is, none of those is the issue here. This is a fault with injectors, injector pump or both. It is not load in this instance. So does the engine not produce any smoke at all when reved to max out of gear???
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Old 04-06-2008, 03:01   #12
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George, you misunderstood Cooper. He is said " All of the above advice may be the problem". It means all suggestions above are possible faults. It is the way we speak down here on the underneath.
Problem is, none of those is the issue here. This is a fault with injectors, injector pump or both. It is not load in this instance. So does the engine not produce any smoke at all when reved to max out of gear???
Alan

To confirm engine does not exibit the problem when reved to 4000rpm in neutral or when trying to replicate load, tied up in its berth in reverse at same rpm.
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Old 04-06-2008, 03:38   #13
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OK, back up a sec. What do you mean trying to replicate a load? Do you mean tied to the dock and throttle wide open in gear??
If you can rev to 4000RPM and it does not smoke, then the IP and Injectors are OK. By the way, you won't "see" a fault with an injector. Not unless you have bionic eye sight.
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Old 04-06-2008, 03:44   #14
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RPM Drop Test
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Old 04-06-2008, 03:50   #15
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Do you mean tied to the dock and throttle wide open in gear??
If you can rev to 4000RPM and it does not smoke, then the IP and Injectors are OK.
Yes - that is exactly the case, although I did wonder if the loading is different in reverse or the prop is cavitating therefore not creating a load as when the problem occurs.

Smoke and soot only accur at 2800rpm when motoring, what does this fact point to or maybe eliminate?

I am going to try and crank engine with injectors removed to see spray pattern. What was also strange injectors were covered in a light brown substance, that when I got on my fingers have been unable to wash off, any idea's?
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