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Old 02-09-2016, 07:43   #16
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Re: Perkins returns black fuel

What are your fuel lines made of? If it's crappy black rubber lines they could be falling apart on the inside and color the fuel. Just a thought.

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Old 02-09-2016, 08:05   #17
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Re: Perkins returns black fuel

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Have you considered taking a sample of the fuel to a lab for analysis? That simple process would identify the origin of the contamination in all likelihood.
This suggestion from Jim has my vote.
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Old 02-09-2016, 10:06   #18
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Re: Perkins returns black fuel

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Originally Posted by RaymondR View Post
This would be my first check particularly if the lift pump actually has to suck the fuel up out of the tank. It explains both the black colour of the fuel and the excessive oil usage. Be mindful that the fuel system returns fuel into your day tank all the time whilst the engine is running via the fuel return line from the fuel pump and injectors and this would explain blackish fuel in the day tank and clean fuel in the main which is not being circulated.
The lift pump is decommissioned on my engine. I've got an electric fuel pump. What baffles me is that my main (ex-contaminated) tank returns clean fuel samples, while the day tank which circulates through the engine returns black sh*t. Discolored, not sludgy.

I indeed had to get "cheap" black rubber fuel lines in the Bahamas.... as an temporary permanent MacGyver solution to keep me going.
So I might have a culprit here now...?
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Old 02-09-2016, 10:37   #19
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Re: Perkins returns black fuel

Thanks for posting all your trials and eventually the solution. good luck
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Old 02-09-2016, 10:56   #20
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Re: Perkins returns black fuel

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Thanks for posting all your trials and eventually the solution. good luck
I will keep you updated. I am taking off the water pump">raw water pump (which seems to be a Sherwood G65) first, to address a leak which is more a constant stream out of a 'telltale' hole indicating the seal is toast. Maybe scorned shaft. When I'm done with this, I'll replace the cheap fuel hoses and flush the engine and Racors with fresh diesel. Then run the engine off of the cleaned day tank also with fresh diesel. If there is no more contamination, it's the fuel hoses disintegrating. If there still is discoloration, I'm back on the drawing board.
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Old 02-09-2016, 12:29   #21
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Re: Perkins returns black fuel

One fine day in Trinidad, I was approached by a low-budget Brazilian yachtie whose engine had died, and who had decided to carry on without an engine. He wanted to sell the fuel in his tanks. I was the color of Starbucks black coffee, but the price was right, so I ran it through my Baja filter and into the tank. My 4108 thrived on the stuff and my filters didn't clog, so I guess black diesel worked OK for me.

In contrast, I got fuel in Aden from a huge wholesale place. It came with a printed analysis, and was as clear as vodka. It also ran fine in the 4108.
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Old 02-09-2016, 14:43   #22
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Re: Perkins returns black fuel

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One fine day in Trinidad, I was approached by a low-budget Brazilian yachtie whose engine had died, and who had decided to carry on without an engine. He wanted to sell the fuel in his tanks. I was the color of Starbucks black coffee, but the price was right, so I ran it through my Baja filter and into the tank. My 4108 thrived on the stuff and my filters didn't clog, so I guess black diesel worked OK for me.

In contrast, I got fuel in Aden from a huge wholesale place. It came with a printed analysis, and was as clear as vodka. It also ran fine in the 4108.
I actually read that you can run a diesel engine with as much as 17% engine oil in the fuel without damaging it. A Perkins 4108 will maybe take 35% or run on olive oil... A lot of trucking businesses pour their used engine oil into their fuel tanks. it will turn your diesel into black devil saliva, but the engine will take it happily. I just don't want to find out which stuff just discolors my filters, and which one clogs them while I'm motoring against 30 knots in a narrow rocky channel.
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Old 04-09-2016, 09:21   #23
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Re: Perkins returns black fuel

Took off the old fuel hoses. Bought new ones.
Still waiting for the raw water pump to be delivered to run the tests. Meanwhile cleaned the dirrrty air intake strainer and emptied the main tank - and found and retrieved a 2 ft brittle hard old once transparent hose in there that apparently was dropped a hundred years ago. Also some sort of old tape strip which could have intermittently blocked my pickup tube. The tank has a 1 1/2 inch inspection port which I am operating through, which doesn't make things easier... maybe there is more in there, seems like a f**cking trash can.

Furthermore, there is still a layer of black sludge on the bottom of the tank which I'll try to suck out with a shop vac. Looks like dead bug sludge.

Well, I'll keep you updated.
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Old 04-09-2016, 09:52   #24
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Re: Perkins returns black fuel

Please let's watch the language, this is a family friendly site.

But I would caution you against a shop vac and fuel, Diesel is hard to ignite, but a shop vac motor makes lots of sparks and could possibly ignite the fuel vapors. Maybe your oil change pump instead?


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Old 04-09-2016, 10:12   #25
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Re: Perkins returns black fuel

If possible, install a proper access port into your fuel tank.
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Old 04-09-2016, 10:51   #26
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Re: Perkins returns black fuel

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Please let's watch the language, this is a family friendly site.
Sorry. I'll cut it.

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But I would caution you against a shop vac and fuel, Diesel is hard to ignite, but a shop vac motor makes lots of sparks and could possibly ignite the fuel vapors. Maybe your oil change pump instead?
You have a point there. I just think the oil extractors hose is too tiny to suck in the blobs of sludge and would clog easily, also I guess if it sucks in air the vacuum is breached?
I'll use a spare fuel pump.
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Old 10-09-2016, 13:31   #27
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Re: Perkins returns black fuel

I ran the engine with the new raw water pump out of a 5gallon jug. So far so nice, all worked well, but for some reason it decided to start smoking / fuming / vaporing out of the mixing elbow / manifold gasket area. Pretty impressive white fumes.

So I decided to further postpone my test program, take off the elbow, clean it, and order a new gasket. There is a small fresh water cooling canal on the bottom of the exhaust manifold and this seemed to leak thru the gasket, evaporate and create this white vapor (because coolant).

Hope that's it.

I'll keep you updated.
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Old 10-09-2016, 19:48   #28
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Re: Perkins returns black fuel

Also, another question, engine related.

Let's assume the bottom is clean, a 37ft not overly loaded down cruising boat, with a clean, 3-blade prop with the correct pitch.

If I want to go hull speed (32' LWL = 7.5 knots ) I have to rev up to 2900-3200 revs on a Perkins 4108?
Really?
Seems like the engine is screaming in pain. I don't get black smoke or anything (and no overheating recently), it just seems unhealthy.

I get 5 kts with ~2300-2500 rpm.

A lot of threads here suggest that boats with a similar length and weight run their 4108 engine around 1800-2000 to reach hull speed.

What could be the cause?
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Old 10-09-2016, 23:54   #29
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Re: Perkins returns black fuel

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Originally Posted by SV gypsy spirit View Post
Also, another question, engine related.

Let's assume the bottom is clean, a 37ft not overly loaded down cruising boat, with a clean, 3-blade prop with the correct pitch.

If I want to go hull speed (32' LWL = 7.5 knots ) I have to rev up to 2900-3200 revs on a Perkins 4108?
Really?
Seems like the engine is screaming in pain. I don't get black smoke or anything (and no overheating recently), it just seems unhealthy.

I get 5 kts with ~2300-2500 rpm.

A lot of threads here suggest that boats with a similar length and weight run their 4108 engine around 1800-2000 to reach hull speed.

What could be the cause?
Transmission gear ratio and/or prop.
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Old 11-09-2016, 08:17   #30
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Re: Perkins returns black fuel

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Transmission gear ratio and/or prop.
Both transmission and prop have not been altered since I have the boat.
She did 5 - 6 knots two years ago @ ~2000 rpm going against wind and sea.

I can turn the shaft freely with one hand while in neutral.
There is no dark smoke or other signs of overloading.

So it must be something that happened / deteriorated gradually over time..?
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