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Old 21-07-2013, 13:57   #1
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Fuel in Return Hose is Black

please 'splain why this occurred.
happened before runaway diesel.
perkins 4-108
we had, half way from zihuatenejo to here, was 40 hours into an 80 hour adventure---black carbony looking exhaust--black smoke and black junk in ocean from wet exhaust. looked into fuel and the returning fuel was also black.
is there a simple reason for this or is this a complex problem..please advise...mechanic hasnt seen black fuel nor runaway prior to this, and says he coulda lived just fine n dandy without it, same as me.....
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Old 21-07-2013, 14:59   #2
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Re: fuel in return hose is black

Hey Zee as I understand it, the black smoke is caused by unburnt fuel and the runaway engine is caused by too little fuel getting to the injectors. I will take a wild guess here and suggest you have your injectors looked at.
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Old 21-07-2013, 15:05   #3
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My hunch is the runaway was caused by the fuel pump seizing wide open. Probably burnt a bearing or something in it causing the black fuel In The return. I believe the Perkins 108 has a separate oil supply for the injector pump.
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Old 21-07-2013, 17:50   #4
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Re: fuel in return hose is black

A runaway is generally caused by oil getting past the rings and burning. The engine oil running the engine overspeeded. In that case the governor should have has the fuel rack shut down to a low stroke under that condition. Betting burnt carbon / combustion gases was forced up into the injectors during the runaway. In my mind that's about the only way it could happen; to have black fuel in the return. I would have the injectors looked at. Though possible, they could be fine
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Old 21-07-2013, 17:53   #5
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Re: fuel in return hose is black

Tiny flying squid slipped into the diesel fuel vent, panicked once inside the tank, ejected black squid ink, which makes your fuel look black. Your biggest problem is if the mama squid comes looking for that tiny one, she'll tear the side of your boat out trying to reach it. Honest, I saw the documentary on the SyFy Channel.

Black smoke, carbon problems, somewhat less likely but I have totally no idea how a diesel engine can make carbon (which has to be made IN the cylinders) and then push that back into the return fuel line. Never heard of this and would suspect it is not something to be ignored. Personally, I'd be reluctant to put any more hours on the engine without a better idea of just what was being burned up, presuming something is.

No unusual noises? Engine putting out normal power? Normal fuel consumption?

Squid filter on the fuel vent intact?
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Old 21-07-2013, 17:54   #6
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Usually I have found that a runaway is caused by a couple problems. First if the crankcase is overfilled the engine sucks oil up and runs away with the crankcase oil as fuel. Second the injectors don't shut done completely after their stroke. Either way once you have a runaway it is common to have black oil in the return line because the injectors are compromised
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Old 21-07-2013, 18:48   #7
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Re: fuel in return hose is black

the carbony stuff came out the wet exhaust....the black diesel fuel went thru the return hose to tank... the stuff in ocean was huge and nasty
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Old 21-07-2013, 19:44   #8
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Re: fuel in return hose is black

My first thought is that you have at least one stuck open injector.

As a result fuel has entered the cylinder(s) on all strokes of the engine (and not burnt).

That unburnt fuel has been pumped into the engine and drained to the oil pan diluting the oil with diesel fuel.

The oil level has risen very high in the engine due to the addition of the diesel fuel.

As a result of the loss of viscosity and the high level you have built up a bit of crankcase pressure forcing the fuel/oil mixture into cylinders and some blackened fuel oil has entered the the fuel return.

Continued running with this condition caused large amounts of the oil/fuel mixture past your rings on the intake stroke causing runaway.

Of course I could be wrong.

What is the level and condition of the oil in your sump? Smell your dipstick.
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Old 21-07-2013, 20:07   #9
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Re: fuel in return hose is black

the black diesel return was on route from zihuatenejo to barra de navidad. oil was changed, fuel was removed and 5 gallons of new clean clear fuel placed.
when engine ranaway, the oil was fresh and so was the diesel fuel. only 5 gal was in tank. oil was perfect.
we started engine and went to raise anchor. while raising anchor diesel began to runaway...within 5 min of onset of runaway status, the injectors were cracked and noise was silenced. there was no over heat and there was no detonate .

bubba was not happy
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Old 21-07-2013, 20:36   #10
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Re: fuel in return hose is black

Oil and fuel in tank were pristine after the runaway?

Have you checked the governor linkage and fuel rack on the injection pump working smoothly?

It's difficult to imagine that the runaway and the black fuel in the return and the fuel tank are unrelated.

I have never worked on a Perkins so I have limited knowledge of the arrangements but runaway engines (engines burning their lubricating oil) usually do so because of two primary reasons - oil moving past the rings into the cylinder due to excessive wear and buildup of crankcase pressure due to exhaust gas caused by wear and inadequate crankcase ventilation.

Good luck.
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Old 21-07-2013, 20:36   #11
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Re: fuel in return hose is black

I have experienced both these symptoms but not at the same time.

The black smoke and exhaust water is usually cause when excess fuel for the engine speed is injected. Before I took to my propeller with a jig saw and removed a couple of inches of diameter I used to experience a black smoke cloud every time I wide opened the throttle. You see this going down the highway when big diesel powered truck do the pedal to the metal thing. If your engine is producing lots of black smoke it suggests that either it is working against an unusually big load or your injector pump is doing the pedal to the metal thing without your permission.

The black fuel suggests that you have suffered a bad case of fuel bug. I did not experience this until I started cruising in the tropics but I then had so many recurrences that I installed a fuel filtering system which circulates the tank to remove it's nasty residue. The bug killer generally works well but occasionally, probably because I have been a little remiss in adding it when refueling I get a recurrence.

I am not familiar with the injector pump system on your engine but many injector pumps are lubricated by the diesel fuel being pumped through them and if the fuel is full of gunk it may explain why your governor is going haywire.
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Old 21-07-2013, 20:40   #12
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Re: fuel in return hose is black

Zee I think at this point you need to consider a complete rebuild of your motor. Not what you want to hear but the smart thing to do.
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Old 21-07-2013, 21:28   #13
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Re: fuel in return hose is black

Based on your description, there is most likely a breach in the rings allowing oil to be mixed with Diesel, or vice versa. Check your oil and see if it has Diesel in it. The first indicator would be veeery low viscosity at colder temperatures.

If that is the case, you need to identify the breach.

Also, the injector pump has a seal that keeps the oil out. When this seal is compromised, Diesel enters the crankcase oil. I'm wondering if the opposite happens...?

After all is said and done, you definitely want to replace your fuel filter, drain and clean your fuel tank, and replace your fuel.
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Old 22-07-2013, 00:35   #14
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Re: fuel in return hose is black

Be mindful that a diesel engine is a compression ignition engine, ie rather than a spark plug igniting the fuel/air mixture, ignition is caused by spraying fuel into the heated air created when ambient air is highly compressed. This phenomena is also responsible for the pre-ignition knock sometimes experienced with petrol engines.

Two stroke diesel engines have blowers which blow all the intake air into and through the sump from whence it passes into the cylinder via slots exposed by the piston when it is passing through the bottom dead centre phase of the piston stroke.

The point here is twofold: If the rings are in so bad condition to allow oil bypass sufficient to significantly increase engine revolutions how are they providing a sufficient seal to allow the air to be compressed sufficiently to allow compression ignition. And. Secondly if this occurs why does not the governor just rack back the injector pump to decrease the fuel load to the engine rather than allowing it to overspeed?

I don't want to start an esoteric argument on these matters but as rugged and reliable as diesel engines are they tend to either wear out very slowly or come apart with fairly violent clunks and bangs. If your engine was not making clunks and bangs before you experienced the problem it is unlikely that it wore out in a few hours.

Most short term onset diesel engine problems involve fuel. See if there is a drain plug on the bottom of your injector pump, drain it out and see if there is any solid residue coming out. If so you may have to have an injector pump service.
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Old 22-07-2013, 01:40   #15
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Re: fuel in return hose is black

Karen,
So sorry to hear about your engine problems. I would do the simple things first..like change fuel filters....look in fuel tank for fuel condition.
The injector pump invariably is lubricated by diesel fuel as it moves through...no other oil there! It is very hard to imagine carbon getting back up into injectors. I would check dipstick to see if oil is MAKING...indicating diesel is adding itself to crankcase and causing your engine racing.
If you have difficulty starting...long time on the cranking....rings may well be worn!

Best of luck!
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