Need drain fuel tank--bad gas. How ???

02-01-2009, 01:03 AM
Need drain fuel tank--bad gas. How ???
Need drain fuel tank.
How do I drain tank ???

02-04-2009, 08:37 AM
Remove engine cover and connect a fuel pressure gauge hose without the gauge to the test port on the fuel rail. Or remove fuel line that goes to the engine off of the fuel filter and connect a hose. In both cases put the hose that you are installing into a gas can.
In the trunk next to the fuse box (between spare tire and battery) remove fuel pump relay, it should be green and it will have a fuse in it. Connect a fused jumper wire between circuit 30 and 87. This will run the fuel pump, wait until the tank is empty.

02-08-2009, 07:03 PM

Youv'e been a big help, but I have a few questions, and still
need some of your help.

I made a fused jumper and connected it as per your instructions.
On the fuel rail, I did something a bit different. I used a regular
valve stem tool, and removed the stem valve, then connected
a hose.

Gas drained well for about the first 4 gallons, then slowed down
a lot, to just a trickle, about 10 minutes to the gallon. I drained
about another 3 gallons, then I disconnected the jumper
because I was afraid that something was going wrong.

So, a couple of questions.
1. Is it supposed to drain this slowly ?

2. Did I screw up the process by removing
the stem valve altogether, instead of using a
pressure tester without the guage ?

3. The gasoline looks much cleaner, not deep urine
yellow like at first, with a separation water line at the top.
Now it's looking clear with a slight yellow tinge., and no
discernable line. Is that right ?

4. After I drained the first 5 gallons, I temporarily reinstalled
the relay, and closed up the fuel rail, and tried to start the
car. It started, which was great, since it was absolutely not
starting before. It is running very rough, but it idles, and I
can rev the engine. By the way, I changed out the CPS a
few days ago and it didn't help. That was before the bad
gas idea came up. Right now, it is idling in the drive way
and still has half a tank of gas. I was thinking of adding s
ome of the dry gas products and see if that helps.
What do you think ? Any advice would be greatly appreciated.

Allso, I am attaching a link to a photo of what I have done.

Again, thanks.

02-10-2009, 03:42 PM
By removing the valve you might have interfered with the operation of the pressure regulator and the siphon jet operation of the fuel tank. Long story short- Not a big deal you just emptyed 1/2 of your 2 sided fuel tank. So you still have bad gas in the tank. Your options are, fill the tank full again and redo, or get under the car and remove both access panels attached to the fuel tank left and right sides. remove the Allen screw plug to access the drain valves no gas behind them. BE CAREFULL doing this next step. Normally you would use a special tool from MB to open the valves but i don't see why you couldn't operate them without the tool they are like a spring loaded valve you can look at them and see, NEVER tried this without the tool. With valves opened the tank will drain. When you are sure the tank is clean, replace the fuel filter and run the pump again to clean out the line to the engine before starting car.

02-10-2009, 09:36 PM
A couple of questions:
1. If I use a pressure gauge, like you recommended, do you think it will drain the rest of the gas ?
2. If I fill up again, will it push the bad gas from one tank to the other, and leave good gas in one tank, and bad gas pushed to the now empty tank ?
3. The valves you mention, do they connect the tanks, sort of like an equalizer, so that I don't have the siphon problem ?
4. Do you know the part number of that tool, and where I might be able to get one ?

Again, thanks. Your a great help.

02-12-2009, 09:24 AM
Mercedes tool # 202 589 00 90 00. cost is ?? You can order one from the dealer. Have you called the dealer to see what the charge would be for them to drain the tank. The cost of them draining the tank may be the same price as you buying the tool. Maybee you could find the tool on E-bay and then when you are done with it put it back on E-bay. Although if you put the valve back into the fuel rail on the engine and connect the correct type of hose, refill the tank, the tank should drain correctly. But that may be a waste of gas. Go to this web site (
select- Access our Training Print Files
go down to the heading - Files for 508 Systems 2 training
select - 508 Systems 2/508 HO Part 07 Fuel supply (WJB) 04-01-01.pdf

Note: you have a Model 208, this will discribe your saddle tank and the operation.

02-12-2009, 09:24 AM

or try this link.

01-18-2010, 01:02 PM
Hi guys doing same job on 95 c280 have a couple questions, when valves behing allen plugs are depressed does gas pour out or do you have too run pump with valves depressed to get fuel out of tank...also sent eclass a p.m....please email me @ thanks Cliff

01-18-2010, 01:45 PM
Did it some months ago. Not certain, but think that it just flowed out w/o running the pump, but not sure.

01-18-2010, 09:33 PM
the pump does not need to be running. i have only used the mercedes tool so look out for the falling gas when the valves are pressed. Try to do this with and empty tank to make things a little easier.

01-18-2010, 09:48 PM
well since the reason I'm doing it is to empty the tank that'll be kind of hard to have it close to empty lol....this car sat for 12-13 years and the gas has got to be junk although I have smelled worse stale gas than this, it stinks! I'm just happy the tank is plastic as I do a lot of classic cars that are steel and of course have the rust issues too...I've had both of the valves open only to have a dribble come out and the tanks may have been empty already, thats why I had to ask about flow and procedure....with the key on engine not running the gauge says a little over 1/2 If it's sposed to pour out with drain button(s) dpressed then mines empty... the gauge is wrong and there was just residual stale fuel left....thanks, and please advise if you think of anything else....Cliff

01-18-2010, 10:23 PM
Here's how I did it. I jacked the car up at all four corners, and had to get it around 1 1/2 to 2 feet high, and made my own tool with a nylon barb that had a threaded base (Ace hardware). I took the aluminum allen cap from the tank to the hardware store so as to get a close match on the thread base of the nylon barb. Nylon is important. Brass would damage the tank aperture threads. The cap is metric, so all you can do is get a close match. I wrapped masking tap around the barb base to take up the gap between the base and the tank aperture, and did a few dry fittings so that I could get it nice and tight. Won't last forever, but it didn't leak, and lasted long enough to drain the tanks. I stayed under the car and kept my hand on the barb throughout. The tank aperture works like a schrader valve, so I trimmed a yellow electrical wire nut until it was the correct length to depress the valve in the tank aperture, then I drilled out the nut so the gas could flow through it, and dropped it inside the threaded base of the barb. I fixed a clear plexi hose to the barb, and screwed the whole thing into the tank aperture, turning the hose as I screwed it in. You need to have the hose connected to the barb because the gas comes out as soon as the Schrader valve is depressed in the tank aperture. The gasoline flows out gently--no dramatic torrent. It's not the easiest thing to work with, but it worked well enough, and I managed to drain both of my tanks of a total of about 7 gallons of watery gasoline. I priced the actual tool at the dealership, and I think it cost about $200.

01-19-2010, 08:50 AM
Yes, well like you I was able to get about a gallon and a 1/2 out with fuel pump initially. thru disconnected fuel line at engine, then pulled the line from tank to pump and only drops came out screen was clean....since theres virtually no free info and questionable pay for info I felt I was only guessing and there could be some M.B. high tech reason for gas not to pour out.Thanks big time to eclass for posting the real benz diagrams and info of fuel system... I have done pretty much the same with fittings on hand however I did also open schrader(s) by hand and propped both sides open with small screwdriver and only got drips...I bought this car halfway thru abandoned accident repairs and have no idea what may have been in the tank in the first place but if opening the schrader lets gas out.... Mines empty...I'll see what the gas gauge says after I get it running...hopefully TODAY!......thanks again for the help!...Cliff

01-19-2010, 09:55 AM
Well I guess spoke too soon..I had'nt been out to the shop yet this a.m when I wrote the last reply....Now I have...Last Nite I shut down all heat and ingnition sources in building and left both the schrader type plastic valves propped open with drain pans to catch last drips of sour gas so I could reassemble and fill with gas and start car this a.m....well overnite the right side pan has filled all the way up approx. 2 gals. and running over and is still dripping, left side has a little bit of gas in that catch pan 1/2 I can only assume that somehow these schrader valves at sending units are some how plugged or a check valve some place is not letting air in the tank to displace the fuel, The gas cap has been off as well as both feed and return lines at the engine and the line going into the left sending to hazard any guesses?....thanks again...cliff

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