Black Gas Out of Tank Drain

[Iconic]

OK, I did a search and didn't find this one.
As advised, I drained most of my fuel out of the larger diameter fuel line between the tank and pump. It had a clear-yellowish appearance.
Then, I unscrewed the tank drain / mesh filter, and out comes black fuel. As black as used motor oil, but thin like fuel.
I tried to read about the flower pot to help me understand how this could be, but I don't understand.
Can someone explain this to me? Is it common? Is it a definite clue to something?
I plan on straining some of the black stuff through a coffee filter to see if in fact it is particles, unless this is a known / obvious answer.
Thanks for your help!!!!!
Mark

[SteveK]

Coming from the bottom of the tank, it could be some moldy water.  Sounds like a good tank cleaning is in order.

[glenn]

Tanks rust. Rust accumulates on the bottom of the tank(seen an inch deep).   The electric fuel pump continuously circulates fuel to the FI pump and back to the tank.  The 10mm return line enters a quart sized holding tank at the side/bottom in a square opening.  The area between the round pipe and the square hole lets the make up gas from the large gas tank enter the quart holding tank.  Rust and gunk plug this area and the pumps starve when the gas level falls below the top of the quart plastic vessel and the quart of gas is consumed.  Engine stops, but will run again when gas slowly seeps thru the crud and fills the quart.    C'est la vie!

[Iconic]

OK, so I think I'm getting it. Please confirm this idea: The screen at the bottom of the flower pot actually turned that black fuel into yellow-clear fuel as I drained it out of the fuel line (can it really strain out the black gunk?). All the the black stuff was held in the flower pot (and bottom of tank) waiting for me to open the tank drain, then whallah, all the black gunk came out?

If I look through the sending unit hole, and I don't see 2 inches of gunk, and I can easily rinse out the remainder gunk ... is it advisable to re-seal the tank or can I rinse and run?
FYI: This is a 78k mile car. Garaged. Tank drain / screen is of original brass design and looks fantastic (and looks original). No red or yellow gunk, no gunk of any kind on strainer. It is possible that someone else before me tried to do all this and didn't get as far as I have gotten (and that is why the screen is clean???). I bought the car in February (not running). It is a very well maintained car. I'm going on the premise that it was parked years ago and not driven. Parked with 16.5 gals of fuel in the tank (not any more). It was parked 3 years ago, but the fuel might be much older based on the fact that it might not have been through a whole tank in many years. TMI I'm just hoping to come to the conclusion of not pulling and sealing the tank.

[ja17]

Hello,

If you do not have debris in the tank, then just add fresh fuel. The dark color may just be some additive to the fuel that remained in the tank.

[johnd]

I would have to throw in some skepticism/negativity. . . .  My tank looked GREAT on the outside and really good as far as I could tell in the inside.  Siphoned a bunch of good gas out.  Then started getting black gas.  Dropped the drain plug/strainer and it had a bunch of rust particles inside.  I would drop it and clean it and coat it or have that done.  My tank just came back from Renu here in TX (no affiliation, but it looks nice).  It doesn't take long to drop it, and you'll know what you have.

johnd
Houston, tx

[waqas]

I strongly recommend John's suggestion below. It doesn't take very much to drop the tank and have it boiled out ($75 last year in Austin from a rad/tank shop). If you have other problems in the fuel system (delivery pump, injection pump, etc, etc), these can be debugged without having to worry about the tank. Ask Michael Salemi why this is important.

[Iconic]

I appreciate all of the ideas you all are giving me, but no-one actually answered my question on how I can get yellow-clear fuel out of my fuel line (larger fuel line to fuel pump) and black as night fuel out of my tank drain hole.
Oh yea, one more fact. Before I started draining out of the fuel line or the tank drain, I siphoned off about seven gallons through the fuel inlet at the back of the car (where I will someday put gas in so I can drive it ). That fuel was just as clear-yellow as what I got out of the fuel one.

Therefore, the black as night fuel was somehow segregated (about a half gallon) to the flower pot, right?
That has to be a clue for something !!!

[waqas]

If you go through the Fuel Tank Tour, you'll find out that the fuel feed line from the tank begins at the base of the flower pot. In fact, it starts right from the drain plug/filter. In other words, the fuel in the flower pot and the fuel in the feed line are separated by the filter attached to the drain plug. So, if the black stuff only shows up when you open the drain plug, then the drain plug/filter is doing its job well!

When you siphoned fuel out, it probably came from outside the flower-pot. So, as you've noted, it would appear that the black sludge build-up is restricted to the flower-pot.

Be warned that there is a little hole at the base of the flower pot through which fuel enters the pot from the rest of the tank. In addition, the fuel return line goes straight back to the flower pot. These entry holes are relatively small and can easily get clogged.

[Mike Hughes]

My impression is that the clear fuel is what resides in the main chamber of the fuel tank, and the sludgy black gunk is what has been introduced into the "flower pot" from the gunk that built up in the fuel lines, injector pump, and fuel return line from while the car was sitting.  You are going to have to pull the sender out and have a look inside to see what is going on there, and how much corrosion the tank may have suffered, if at all.  At the very least you may have to unblock the small hole in the base of the "flower pot" that allows fuel into the "flower pot" when the fuel level falls below its rim.  A length of coat hanger, strategically bent, will do the trick!

[glenn]

First, apply all 'gasoline safety' measures.  Drain the tank.  Remove sender, drain filter, hoses.  Turn tank upside down.  Shake, rattle and roll dried crud and gunk out the sender hole.  Get a vacuum with a long hose(electric motor far from the tank).  Vacuum out tank.  Use a flashlight and wire to make sure the annular square space around the round return line is open.  Flush tank.  Recheck.  With a flashlight and flex mirror you ought to be able to see all the tank insides. 

[Iconic]

FYI: I ran the black liquid through a coffee filter and it went right through without leaving much debris and stayed black. So, my theory about the strainer in the tank drain turning black fuel to yellow-clear was not correct. So, the black fuel must have been restricted to the very bottom of the tank in the flower pot. I looked through sender hole (everyone makes it sound so easy, it isn't !!!). The tank is very clean inside. My latest theory is someone else went through all this, but failed to get the car running LIKE ME. Yes, today it started for the first time since I bought it on February 22nd (2009). I changed the fuel hoses in back. I replaced the fuel pump (I needed to get this thing running for my sanity, so me rebuilding was not an option). Drained and inspected tank. I clamped the bypass fuel line near the pump to make sure I had flow through the whole system all the way back to the tank. I didn't read that one. I was surprised no one wrote about that. (Maybe someone did and I didn't see it.) I'll write a little more in the General section about the start up. Thanks for all your help.

[ja17]

Hello,

I like Mike Hughes' theory on the black fuel, but just the opposite.  The flower pot would drain first, then the black gas from the outer tank would trickle into the flower pot and drain also.

[Bob G ✝︎]

There is some good subject matter here. I know thanks to Joe Alexander who took us on a step by step tour of the workings of the gas tank design.  I would like to ask a question since I cannot fine the information in my old records.

two items on my to due list on my 1968 280SL is to remove and replace the gasoline engine filter & tank filter.All this will Be done when I run into the reserve part of the gasoline supplied in the tank? How much is in reserve? I do not want to burn up the fuel pump by starving it for fuel and raising the temperature of the pump which is cooled by gasoline.

what kind of siphon pump can I purchase for this service?  Also being around such a flammable substance besides removing the negative battery lead and rapping it in a towel is their any other precautions I should to take beside wearing safety goggles and gloves.

Is their any further work I can do with out removing the gas tank while I do this proceeder? Also is the current supplied tank filter changed from the original. do I need to order a special washer for the hex nut?

When I refill the gas tank how long will it take to prime the pump and start the engine so I can refill at the gas station?

Thank you
Bob Geco

[Peter van Es]

Bob,

you'll find answers to many of your questions in the Technical Manual at http://www.sl113.org/wiki/Fuel/Tank

Peter