Fuel Tank Tour

[ja17]

Hello Matt,
Congratulations and let us know when you have it on the road!

good idea on the guitar string!



Joe Alexander
Blacklick, Ohio

[Miloslav Maun]

I have just read this whole thread and I think that I have found the solution for my problem: After reinstalling the tank into my freshly restored car, the fuel pump does not supply enough fuel.
We have inserted the otulet fuel tube from the pump into a glass canister and we can see that right after the pump starts, the flow is strong. In a couple of moments the current becomes weaker and probably not enough to satisfy the engine.
According to what I've just read I presume that the inlet hole in the shell reservoir (or as you call it the "flower pot") is clogged (there is about 20 liters of fuel in the tak now, probably below the reservoir's edge).

Is it likely that the hole got clogged when the tank was out of the car? Before there was no such problem. The only thing we did with the tank was that it had beed cleaned with pressure water and eventually dried on the sun.

My second question is: How come that the fuel current from the pump is always strong for a second or two after the pump is started? Is the opening in the shell container just partially clogged (and thus when the pump is off the levels can ballance)? Can it be widened with a wire or file driven through the sender unit?

Thanks for your ideas and thanks for this whole helpful thread!

[Naj ✝︎]

Muf,

I would start with the filter screen and make sure its not clogged up.
While its off, you can insert a wire into the outlet pipe from the plug opening and clear it out. You can clear out the return line as well while you are there. I found an old outer heater cable very handy for this job.

naj

68 280SL

[ja17]

Hello Muf,

Be sure to check the small fuel screen in the intake fitting of the electric fuel pump.  It can become clogged very easily. Earliest versions of the 230SLs did not have it however.

Fuel delivery problems frequently show the symptoms you have described. At rest fuel is allowed to seep past any restrictions after a period of time. So when the electric fuel pump is started the fuel flow may be strong for a few minutes. My first suspect would be the fuel screen in the electric fuel pump. Next check the intake passages in the gas tank "flower pot".

Joe Alexander
Blacklick, Ohio

[merrill]

well, so close yet so far,

Finall got to the point of putting fuel in the tank and try to start the car.

finished all the other projects, put 5 gallons of fuel in the tank and not one drop of fuel came out of the tank.  (via clear fuel filter before fuel pump)

drained the gas, pulled the tank, again, and tested the flow.
filled the tank with water, not over the top of the flower pot and the water flowed out the fuel feed outlet slowly.

drained the water,  filled only the flower pot and the water flowed very strong.

SOB.  I guess the fuel inlet into the flower pot has a clog.

took the tank to the shop today, to have it boiled, cut open and check the inlet.  

guess it pays to check this before installing the tank

matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[merrill]

Finally, picked up the tank from the radiator shop, they installed an access plug to the left of the inlet - outlet tubes so if there is ever another problem one can get a tool inside the tank.

painted the tank,installed it, put 5 gallons in it, ran the pump,  and STILL  NO FUEL came out!!!  let the pump run for a short time,  still no fuel.   drained the tank, checked the fuel screen, it was ok, reinstalled the screen, put some fuel into the flower pot and no fuel came out.

insterted a clear poly line into the large fuel tank outlet tube, applied a vacuum and some fuel came out,  hmm.

hooked everything back up again, still no fuel,  pulled the suction pipe off the pump, could not really feel a vacuum.  Now realy frustrated.  

hooked everything back up again,  and wondered, maybe the sustem needs to be bled.  So, went to the engine compartment, disconnected the fuel return line and applied vacuum till fuel came out.  checked my fuel filter back at the tank, and finally fuel was present.

then, hooked the return line back up, turned on the key to position one and I could see the fuel being sucked thru the clear fuel filter I installed near the tank.

Bottom, Line, when the sysem has been opened, first bleed the system up in the engine compartment to get the air out and fuel into the pump and system.

matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[ja17]

Hello Matt,

The electric fuel pump is basically gravity feed. It will not pull much vacuum at all. The electric fuel  should be mounted correctly near  the lowest level of the fuel tank. Make sure the pump mountings and brackets are correct so that the fuel pump is at the correct level so fuel will flow  easily to it's intake. Once the fuel is present in  the electric fuel pump it should prime up fine if the system is ok.

Joe Alexander
Blacklick, Ohio

[tuultyme]

When I filled my tank full for the winter I smelled fuel.  Looking under the car I noticed a leak from the top front of the tank.  When I took the senser out last year I did not see any corrosion in the tank; put in a new seal at the time.  Before pulling the tank are there any fittings at the top that may be leaking?  Could the tank rust where it might be touching the tunk floor?  After driving the car to lower the fuel just some the leak is gone.

Bruce; 268Blaugrun(green) 1970 280SL; IL

[merrill]

Bruce,
I am not sure, but on the 230 there are 2 rubber lines under the cover for the fuel filler neck.  those can get old and leak.

also if you have the fuel tank vent system mounted on the inside of the passenger fender make sure the rubber hoses for it are not leaking as well.

on my sl, I actually had fuel on the top of the tank where the fuel sender is installed,  replaced the cork gasket and no leak.

matt

Matt
66 230 sl - "white"
78 300 D - Blue
98 C230

[Miloslav Maun]

How high is the "flower pot"? I mean how much fuel must be in the tank so that it can go over in the pot?

[Mike Hughes]

If you pull the fuel sender out (accessible from inside the trunk) you can look inside the tank and see the flower pot.  It's probably 4-5 inches high, so I'd estimate that the tank would need to be at least 1/2 to 2/3 full to overflow the flower pot from the top.

quote:Originally posted by Muf

How high is the "flower pot"? I mean how much fuel must be in the tank so that it can go over in the pot?

- Mike Hughes  -ô¿ô-
  1966 230SL Auto P/S
  Havanna Brown (408)
  Light Beige (181)
  Cream M-B Tex (121)

[merrill]

Muf,
the fuel enters the pot at the bottom not over the top.


see the photo fuel tank with fp ill..JPG


matt

Matt
Austin Tx
66 230 sl - "white"
78 300 D - Blue
98 C230

[Miloslav Maun]

Matt,
I know the fuel is supposed to enter from below but I am afraid it does not. When the tank is less than about 1/2, the car stops entirely. I guess the dirt clogged the entrance hole next to the return tube. :-(  Is there a way to clean the hole apart from brutally opening the tank?

[ja17]

Hello Muf,

The fuel tank can be drained, remove the fuel sender unit in the trunk, and used a long air nozzle and compessed air to clear the intake to the "flower pot". You can also work a wire in from the fuel sender opening to help unplug the intake port.  

Matt, fuel will fill the flower pot once the level in the tank is above the wall of the flower pot. However if the intake port is plugged the engine will starve for fuel once the level of the fuel in the tank is below the wall of the flower pot.

Exteme caution must always be taken when dealing with gasoline.  Sparks, trouble lights, static electric etc. will ignite fuel or fuems. Be careful! Store all drained fuel in good sealed containers, work outdoors in good ventilation if possible, and have an extinguisher close by.
 
The theory behind the flower pot design is that it keeps plenty of fuel on hand for the engine even when the tank is nearly empty or even under sever cornering conditions. Dan Caron also has a good theory that the swirling flow of the fuel in the flower pot creates a venturi effect which also cools the fuel.

Joe Alexander
Blacklick, Ohio

[Mike Hughes]

As I mentioned earlier, pull the sending unit.  This is accessible from inside the trunk.  Just gently pry up the round plastic plug, remove the square wiring conector, and remove the five nuts and washers.  "Gently" pry with a small angled tool around the circumfrence of the sender until it loosens from the gasket and pull straight up and out.  Peering inside with a flashlight, you will be able to see the flower pot, and the fuel feed (large)and fuel return (smaller)lines.  You can also check around for signs of rust. A small adjustable mirror is very useful for this.  Just don't loose any tools inside the tank as they will be the devil to fish out!

The intake to the flower pot is below the return line.  I was able to bend a length of coat hanger and insert it into the intake.  If you can get about two inches of wire into the intake you will very likely clear the blockage.  Be sure to allow a bit of "curve" when you bend the wire to follow the curve of the flower pot.  

If the inlet was blocked, chances are your in tank fuel filter is pretty clogged, too.  Jack up the rear of the car and drain the tank by undoing the hose from the tank at the fuel pump and let it empty into several gasoline cans that you have standing by.  Then unscrew the drain plug.  You will need a 22mm bolt head and some way of turning it to undo the drain plug.  (Hint: a kingpin trunnion bolt has a 22mm head. The bonus is it has a castellated nut that can be prevented from turning if you substitute a hardened steel pin in place of a cotter pin.  I found a finishing nail punch that fit the cotter pin hole and worked a treat!  Do not turn the bolt with the punch - it will break off!  Use a box wrench on the nut itself to turn the bolt.)  You will also need an oil drain pan to catch the remaining fuel as it drains out.  There will probably be some debris in the pan when you are all done as well.  Once out, hold the in-tank fliter/drain plug up to the light.  If you can't see light through it, gently blow it clean with compressed air until you can see light through the plastic screen.

Now that you have drained your tank till it is almost empty and removed, cleaned, and replaced the in-tank filter/drain plug, you can check to see if your inlet is unplugged by peering into the inside of the flower pot.  Using a funnel, fill the flower pot to the brim with gasoline.  If it empties out into the tank, you have unblocked your intake.  Add maybe one gallon of gas and you can also check your fuel pump and return line by turning on the ignition and peering into the flower pot.  You should see fuel swirling around clockwise inside the main chamber of the flower pot and the level of fuel inside the flower pot should rise somewhat.  You may also hear some gurgling as the pump purges any air from the fuel feed and return lines.  Keep running the pump until you have a strong quiet flow.

Reassemble everything and it should start right up.  You are now an expert on 113 fuel tanks!

quote:Originally posted by Muf

Matt,
I know the fuel is supposed to enter from below but I am afraid it does not. When the tank is less than about 1/2, the car stops entirely. I guess the dirt clogged the entrance hole next to the return tube. :-(  Is there a way to clean the hole apart from brutally opening the tank?

- Mike Hughes  -ô¿ô-
  1966 230SL Auto P/S
  Havanna Brown (408)
  Light Beige (181)
  Cream M-B Tex (121)

[ja17]

Hello Mike,
Nice step by step description!  Denatured alcohal works best on cleaning varnish of the drain screen.

The carbureted Mercedes cars of the era had no flower pot in the tanks. The fuel demands of on a carbureted engine were much less.

Joe Alexander
Blacklick, Ohio

[merrill]

Mike, Joe, Muf,
the lower flower pot inlet in the tank on my 66 230 sl  was plugged.

I took the tank to a repair shop and they installed a screw in  plug that I could remove and clean out the lower flower pot inlet.

the plug is located at the correct position so when removed one looks right at the lower flower pot inlet.

matt

Matt
Austin Tx
66 230 sl - "white"
78 300 D - Blue
98 C230