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Old 04-02-2016, 21:13   #1
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Location: Antioch CA
Boat: Cal 39
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Black Fuel

I have a Perkins 4-108 in my 1971 Cal 39. The original engine was a Perkins 4-107. My fuel turns black after it has returned from the high pressure pump. It is obviously getting lubricating oil in it. Years ago when I was doing deliveries I had a boat where the oil level on the dipstick rose and there was lube oil in the fuel going to the injectors. A mechanic in Santa Cruz told me not to worry for the remainder of the delivery to Southern California because "a diesel engine can burn lube oil just fine."It is NOT diesel bugs or any other thing in the tanks. I have had the tanks scrubbed and the fuel polished. The boat has two fuel tanks. I put clean fuel in one tank and put the return fuel in the other. The clean tank stays clean. The "return" tank has black fuel. I'm not sure, but I think that lube oil is getting into the fuel in the high pressure pump, but having the pump rebuilt seemed to do nothing. The engine runs fine. It does not smoke (except upon startup for a few seconds). It's been this way for the last 8 years, including a couple Baja Bashes (and attempts of repair by mechanics in San Diego). Is there anbody on this forum that has had a similar problem? And how was it solved?

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Old 04-02-2016, 21:23   #2
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Re: Black Fuel

If there is mixing of fuel and oil going on, have an oil sample tested to see if any fuel ends up in the crank case.
Had 6% fuel in the oil of my 4-108 but from a bad lift pump.

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Old 06-02-2016, 06:21   #3
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Re: Black Fuel

I had a similar problem. The diaphragm pump on a Universal (Kubota) engine was sucking crank case oil into the fuel. The pump was located before the primary fuel filter which got fouled very quickly.

I had an inline electric backup fuel pump in place so I by-passed the mechanical pump and solved my problem until I could replace the mechanical. To stop the mechanical from simply pumping oil out of the crank case, i looped a hose from the intake to the output fittings on the pump.

Hope it is not your high pressure pump.
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Old 06-02-2016, 06:58   #4
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Location: Nice, France
Boat: Hunter Marine 38
Posts: 151
Re: Black Fuel

AFAIK the high pressure pump is lubricated by the diesel fuel only. Must be the diaphragm pump.
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