Outer Limits 4x4 Board

I have a boat with 2 GM detroit 6V53T,s in it, im having problems with fuel contamination, it appears that engine oil is getting back into the fuel return lines. We cut the tanks open and scrubbed them spotless, within a few days of running the clean fuel had gone black again. Is it possible for oil to get back into fuel returns, maybe through a fuel pump seal or injector or something similar????? if there is someone here that specializes in detroits near the gold coast or brisbane i would be happy to pay you to come and have a look and fix it.

The only thing I can think of is that the fuel passes through galleries in the head. At no point in time fuel comes into contact with the oil. The only way I can see this happening is that there might be a crack in the passages somewhere, but fuel is at a higher pressure, so one would think that fuel would end up in the oil not the other way round.

simkell wrote:The only thing I can think of is that the fuel passes through galleries in the head. At no point in time fuel comes into contact with the oil. The only way I can see this happening is that there might be a crack in the passages somewhere, but fuel is at a higher pressure, so one would think that fuel would end up in the oil not the other way round.

We had the opposite problem with injector lines leaking into the oil as they passed through the head. I'd be looking at any location where oil pressure is greater than fuel pressure, particularly with return lines after the injectors.

Are you running a fuel cooler? I know the bird frighteners run the fuel as part of the cooling system and fuel tank temps can get high even WITH a cooler. check that it's actually oil and that you're not coking the fuel or something stupid like that.

MILO

Interesting theory milo, it does have a fuel cooler so i will look into this. i might take a sample of the fuel in to a lab and see if they can analys what the contaminent is.

Hey mate,

Just a couple of possibilities, fungus is common in marine applications or carbon from injector tip blowby.
It probably won't be a fuel rail as you would be making oil as well.
Depending on the model will determine where the pickup pump is mounted but I think there is a tell tale hole to let you know if one of the seals fail so worth checking.

Cheers smithy

hammey wrote:Hey mate,

Just a couple of possibilities, fungus is common in marine applications or carbon from injector tip blowby.
It probably won't be a fuel rail as you would be making oil as well.
Depending on the model will determine where the pickup pump is mounted but I think there is a tell tale hole to let you know if one of the seals fail so worth checking.

Cheers smithy

Pretty certain its not fungus, we cut both tanks open and scrubbed them and have done several treatments with fuel doctor and the black stuff just keeps coming back.

Hi Mate, No experience with this engine but on some caterpillar diesels the diesel fuel injectors are actuated by oil pressure from the engine oil. Possibly if its the same or similar system then you've got an injector problem, possibly only one by the sounds of it. This would explain why you're only getting oil in the diesel and not diesel in the oil as the oil is at higher pressure than the diesel. Hope this helps. GT

Gordy wrote:Hi Mate, No experience with this engine but on some caterpillar diesels the diesel fuel injectors are actuated by oil pressure from the engine oil. Possibly if its the same or similar system then you've got an injector problem, possibly only one by the sounds of it. This would explain why you're only getting oil in the diesel and not diesel in the oil as the oil is at higher pressure than the diesel. Hope this helps. GT

detroit don't run HEUI injectors. check the seals in the injector pump around the governor. but as has been said, the fuel is at higher pressure than the oil in almost all areas and if your not making oil and its both engines running full separate fuel systems?

As luck would have it. I've just done a cat 1.1 motor today with the same symptoms. 2 loose injectors were letting combustion gases past the injector seals and blackening the fuel being returned to tank. Might be worth checking out. Do the engines run fine?

chunderlicious wrote:As luck would have it. I've just done a cat 1.1 motor today with the same symptoms. 2 loose injectors were letting combustion gases past the injector seals and blackening the fuel being returned to tank. Might be worth checking out. Do the engines run fine?

One motor is running perfect, the other which i think is the one blackening the fuel is running good, but sometimes it wont make full revs, im going to put a valve in the marriage line that joins both fuel tanks so i can isolate the problem to one motor.