Perkins returns black fuel

[SV gypsy spirit]

Preface:
I am pondering over fuel ******** I found out today. Originally, I was about to pull the water pump">raw water pump because of a slow leak. To do this, I had to pull out my day tank to get access to said pump. While doing this, and peeking into the tank seeing "dark" fuel, I came up with the idea of changing my two in line racor fuel filters, which turned out to be both black as the devils wallpaint. So I went on on this route, and got a fuel sample out of my main tank and one out of my day tank.

So, forget about the raw water pump. Here's my fuel set up (Gulfstar 37 with a Perkins 4108) :

1.) 35 gallon Main tank is disconnected from any engine fuel lines and solely serves the day tank through a racor 10 micron filter by a manually activated electrical fuel pump. (Was installed as a "quick fix" to a bad case of diesel bug)
2.) From the 13 gallon day tank, the major fuel line to the engine goes through two more Racor 500 filters, 30 and 10 micron, serving as secondary and primary fuel filters. The primary fuel filter on the engine has been removed. There is an electrical fuel pump that feeds directly into the injector / high pressure pump.
3.) The engine returns excess / surplus fuel to the day tank.

So my fuel samples came out quite different than I thought: The allegedly contaminated main tank fuel sample came out pristine clear, the day tank sample came back black. Like, black.

Also, I've been low on oil just in the last months. The engine seems to eat oil faster than I was used to. I'm not "making" oil, and the dipstick sample is thick and looks as usual, so I assume no diesel gets into the crankcase? To me it seems, the surplus fuel comes back contaminated with what I think is engine oil. 15W40. What-the-eff?
Compression seems super fine, engine always starts right away and runs smoothly, so I kind of tend to rule out bad rings.

What else would turn my fuel into black goo? Mind you, the main tanks diesel is fine and clear.
Thank you for any input or ideas!
Dan

[Lepke]

I have a 4108 on a generator. If oil truly is getting into the fuel, the injector pump is the only common factor. There is a seal at the drive end that if it fails usually allows fuel into the oil. The pump runs opposite the sw pump and the gear housing only slings oil from the bearings. The oil pressure would only be at what ever crankcase pressure is. The fuel side has the real pressure to push fuel into the gear housing with seal failure.
I think you still have a bio issue in your tank/fuel system. Use a good diesel biocide, put a 2 micron where the 30 is and circulate. If you don't have one, put a vacuum gauge after the fuel filters but before the electric pump. Then you can tell by changes on the gauge, how dirty your filter is.
I use diesel treatment every time I take on larger amounts of fuel. I run 2 micron filters in my primaries all the time (after solving inital problems when boat was purchased). I hold 2000 gallons in 4 tanks and never have bio problems.
If you decide you have a bio problem and want a detailed solution, send a pm. I rarely reread subjects I post in.

[DeepFrz]

What else would turn my fuel into black goo?

Add a little (few drops) of chlorine bleach to a small sample of the fuel. If the fuel changes color then you likely have bio contamination.

[donradcliffe]

I agree with Lepke. I'd dose the day tank ,and change the final filter to 2 microns.

[SV gypsy spirit]

Alright guys thank you so much for your replies.

First of all, I've been doing the quick bleach test by taking a sample of my day tank fuel into a transparent bottle, and poured some bleach in it. Still looks like Coca Cola. Although now there is a layer of bleachy water it was diluted with, and a thin layer of black particle stuff on top of the water layer. And then the coke colored diesel. Which may or may not be a littttttle brighter colored than before. So, I don't know.

What I am going to do is get two 5 gallon jugs of good fresh yellow colored american gas station diesel, use the first one to flush the whole fuel system including draining and refilling the racor bowls, until there is no more red/dark diesel in there. Then run the engine out of the other yellow diesel jug and have the return lines go into this same container. Run it for say 4 hours through 10 and 2 micron filters on ~1200 rpm. The fuel return rate is pretty high, so the fuel gets "polished" or either contaminated. Or not. So with this I should be able to tell if the "black" contamination is coming from the engine whatsoever, right?

On the other hand, my fuel filters were black, but not clogged. I actually do have a vacuum gauge on the secondary filter. I had a fuel bug as said, and it made the engine run away and die due to clogged filters, so I know the signs and symptoms of this. But right now, the fuel and filters just seem discolored but not sludgey or slimey or clogged.

[silverfern]

With engine oil disappearing then my first check would be the the fuel lift pump. This is common for perkins.

Bob

[SV gypsy spirit]

Originally Posted by silverfern

With engine oil disappearing then my first check would be the the fuel lift pump. This is common for perkins.

Bob

Thank you; so as far as I understand a leaking diaphragm of the lift pump would allow oil into the fuel but not fuel into the oil? (Before I take it apart?)

[CHRIS V CLEMENT]

I have a 1973 Perkins 4-108 that had a similar fuel injector issue. I had a very small external fuel leak at the high pressure pump where the throttle cable is attached. Rebuilding of the high pressure pump made the engine run like a new machine. I had the injectors checked at the same time...no issues. I have seen no black fuel, but my leak was external...
Good luck and Good Sailing...

[DeepFrz]

First of all, I've been doing the quick bleach test by taking a sample of my day tank fuel into a transparent bottle, and poured some bleach in it. Still looks like Coca Cola. Although now there is a layer of bleachy water it was diluted with, and a thin layer of black particle stuff on top of the water layer. And then the coke colored diesel. Which may or may not be a littttttle brighter colored than before. So, I don't know.

Doesn't sound like biological contamination then. The slight color change is probably just dilution with the bleach. If you had a white layer on top of regular colored diesel i would suspect bio. contamination.
Good luck.

[zeehag]

black fuel from return?? lift pump fail compounded by injector pump fail.
how much oil on dipstick or have you checked yet-- mine did this just before runaway.
check lift pump and oil level. change oil then observe. observe very closely. mine did black diesel via return hose into tank then at almost 300 miles, ranaway. oops. black smoke--unburned fuel. injector pump....

[tinkrman69]

sounds like injector pump to me too. also, did I read right? you have two filters from the tank then an electric fuel pump going straight into the injection pump, with no filter betwixt that pump and the injection pump? junk from an electric pump can really screw up an injection pump. The primary filter that was removed was the last line of defense for the more expensive parts of the fuel system.

[Lepke]

Your original descriptions state you use an electric fuel pump. That usually means no manual engine mounted lift pump is used. If you have a diaphragm lift pump, a rupture of the diaphragm could allow fuel into the crankcase. One side of the diaphragm is fuel and the other side is exposed to the crankcase. It is unlikely oil would go into the fuel because the oil in that area is from splashes and the fuel pressure should be higher than the crankcase pressure.
Even after killing all organism, the black color can persist until diluted with new fuel. Buy a good (expensive) fuel conditioner with a biocide. Mix at 2-3x the normal rate to kill organisms. There 2 types of conditioners for water in the fuel. One makes the diesel absorb the water so it burns and the other helps the water separate out so the racor will catch it. Either works. The conditioner will also make the existing fuel burn better.
If you put in a 2 micron in the 1st filter housing it will keep debris out of the rest of the system while circulating. You have such a small amount of fuel, the filter probably will not plug. When you're done you can go back to the 30 micron.
I run 2 micron primaries all the time because my fuel and tanks are clean. About 5000 gallons are filtered before the 2 micron shows signs of plugging.

[RaymondR]

Originally Posted by silverfern

With engine oil disappearing then my first check would be the the fuel lift pump. This is common for perkins.

Bob

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.

[Jim Cate]

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.

Jim

[svJasmine]

99 percent chance this is a bad lift pump diaphragm.

To be sure, hook up an electric pump, disconnect the original pump, and I use a small dinghy tank to test. Return the fuel in to a small glass container.

It will tell you for sure.

Rich