The Chicken & the Egg Game, or To Re-tank or Not Re-tank Mike's '72 280SE - Mercedes-Benz Forum

 
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post #1 of 6 (permalink) Old 06-30-2014, 01:28 PM Thread Starter
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The Chicken & the Egg Game, or To Re-tank or Not Re-tank Mike's '72 280SE

My friend Mike has a '72 W108 280SE, with the M130 six.
His gas tank has lots of rust & crud in the bottom and the car has become undriveable. It also had several gallons of pretty old, stale gas, which I was able to pump out, along with alot of rust, after pulling the gauge sending unit.
There's also a plastic well surrounding the in-tank screen that's plugged. I've been told that the top of the tank would need to be cut open and the plastic well replaced.
The only place in the DC area that repairs gas tanks wants up to $600 and I don't know how good they are. Considering the PO ckaimed he had the tank repaired locally before Mike bought the car.
So before Mike invests in a $600 tank repair job, or a tracks down a couple leads on 'good' used tanks, I'm fitting a 6-gallon outboard-motor tank in his trunk and running a hose to the electric pump to see if the problem is in the tank, or there's more trouble with the fuel-injection system. There's a possibility that crap got sucked into the fuel injection since I discovered the fuel filter had been installed with both gaskets on the bottom and none on top!
I actually hooked up the outboard tank a couple weeks ago and the car seemed to run better sitting in the driveway, but we weren't able to drive it around with the outboard tank loose in the trunk.
My question is - how important is the fuel return line. My outboard tank has no fitting for a fuel-return line, and I didn't want the fuel system pumping gas from the outboard tank to the car's gas tank, so I simply plugged it during the test. For the re-test, I'm willing to secure the outboard tank and add another fitting for the fuel return if someone here thinks the return is critical for testing.
The situation is also complicated now by a buyer that wants to buy this car as-is, so we need to decide if it's only the tank or there's another can-o-worms looming!
Thanks in advance.

Happy Motoring, Mark
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post #2 of 6 (permalink) Old 07-04-2014, 06:33 PM
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Plugging the return line? I'm surprised the car didn't stall from being over rich. If you do take it for a run, unplug the return line and hook it into your temp tank.

My recommendation is that you take the top and filler caps off the tank, remove the screen (the huge hex nut at the bottom), take the tank out of the car and spray the thing out with a power washer, or at a local car wash place. Empty, the tank weighs about 20 lbs or so - it's light and easily manageable. Allow it to dry (or dry it with or in something warm), and then recoat the tank with any number of aftermarket products. Eastwood.com has them, POR has them, I'd wager you could buy the sealant even at Napa or Autozone. Not counting your own labor and the cost of a car wash, you could do this on your own for about $75...
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post #3 of 6 (permalink) Old 07-05-2014, 04:54 AM Thread Starter
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Originally Posted by Grubeguy View Post
Plugging the return line? I'm surprised the car didn't stall from being over rich. If you do take it for a run, unplug the return line and hook it into your temp tank.

My recommendation is that you take the top and filler caps off the tank, remove the screen (the huge hex nut at the bottom), take the tank out of the car and spray the thing out with a power washer, or at a local car wash place. Empty, the tank weighs about 20 lbs or so - it's light and easily manageable. Allow it to dry (or dry it with or in something warm), and then recoat the tank with any number of aftermarket products. Eastwood.com has them, POR has them, I'd wager you could buy the sealant even at Napa or Autozone. Not counting your own labor and the cost of a car wash, you could do this on your own for about $75...
Thank you for the reply.
The car has been running rich for a long time, until a few weeks ago when I replaced the fuel-injection thermostat and unstuck it's piston. Then it seemed to start running too lean after warmup and stalling repeatedly. Mike could barely get it back in his garage. By then, Mike hadn't been driving the car much, so the gas was pretty old. Mike bought a hand-pump and we proceeded to pump out about 5 gallons of stale, nasty gas before we put fresh gas in it. That's when we discovered how much crap was in the tank. I tried to suck as much of it as possible with the hand-pump through the sender-opening. Then I replaced the main fuel filter and discovered the old filter-cartridge had been installed without the felt washer on top. So I'm now worried that has allowed junk into the fuel-injection pump. When I tried the outboard tank, maybe it ran better because plugging that return-line richened it up temporarily.

I'm also worried any gas-tank coating will permanently plug the holes in that plastic pot inside the tank - which currently seems to be plugged by rust & sludge. Before it got so bad, Mike had an issue for years where the car would only run right on a full tank. Once the tank got down to less than half, it became unreliable and would stall-out frequently. The guy that sold Mike the car has owned several Pagoda SLs and done alot of work on them. He said that in-tank pot being plugged could be part of the problem.

I still need to add another fitting to that outboard-tank
I guess if it starts running badly again with the return-line connected, the fuel-injection pump may be messed up too!

Happy Motoring, Mark

Last edited by Mark DiSilvestro; 07-05-2014 at 05:01 AM.
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post #4 of 6 (permalink) Old 07-05-2014, 09:32 AM
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Crappy running below half a tank tells me the inner pot is plugged. At low levels, that pot is designed to keep gas at the exit and not sloshing around.

Sealant, whether applied by a shop or by you, is sealant. The stuff is actually pretty thin.

In my experience, and I consider myself a shade above a novice when it comes to car mechanicing, the only thing a mechanic does for me is provide the labor so I don't have to do it myself. This really is a pretty easy/manageable job. Just read the directions on the product you buy.

Not that I'm plugging Eastwood, but they have a tech line that can answer a lot of questions - I use them when it comes to undercoating and epoxy sealants.
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post #5 of 6 (permalink) Old 07-06-2014, 01:09 PM
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I also use the local power wash...I spray a whole can of Easy Off oven cleaner and plug all the holes and let it sit for about 30 mins, then take it to the local high pressure spray wash. If I tank is really bad I do this twice. Had to do it on my 78 280SL and the car ran fine after this cleaning and replacing the strainer screen. If the tank is going to sit for a period of time I dump a gallon of Diesel in and slosh it pretty good to keep it from flash rusting.


Al
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post #6 of 6 (permalink) Old 07-09-2014, 07:40 PM Thread Starter
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So, after modifying my outboard tank to add a return-line fitting, we were able to test drive Mike's SE quite a bit today. It drove perfectly except for a lumpy, unreliable idle when in R or D. For now, a slight adjustment of the idle-air screw, and a more significant adjustment of the idle mixture screw has smoothed-out the idle to help keep it running while idling in gear, until I can check out the anti-stalling solenoid, which isn't getting any power. According to Mike's FSM, tranny oil-pressure switch #17 signals a control-relay box to bump-up the engine speed 180 rpm if the idle drops below 600 when in gear.
Meanwhile, it looks like we'll be pulling the tank soon to clean it out, and see if I can POR15 it.

Happy Motoring, Mark
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