Pressure Buildup in Gas Tank

[Travis71280]

Hi all,

I have been in the process of restoring my 1971 280sl trying to get it road ready when I ran into another roadblock. Previously I've had issues with the lack of fuel flow in the injection pump as a result of a faulty check valve on the return side of the injection pump causing the pump to overheat to the point of stalling via vapor lock. I ended up drilling out the check valve and incorperated an aftermarket pressure regulator on the return side to solve the problem. Now I'm having issues with the gas tank building too much pressure (I believe its either building pressure or vacuum) to the point where the fuel injection pump starts overheating and eventually causing the car to stall out. The car was equiped with an expansion tank in the back, but the vent hose on the passenger side of the filler neck is completely cloged up from when I relined the tank and the one on the driver side I believe still free-flowing. I tried to remedy the problem with a Stant gas cap for a 1969 (which was vented) but ended up with the same result. Is the vented gas cap defective, or is there something else I can do to resolve the situation? Any help is appreciated.

[Richard Madison]

1969 280SL had a blockage in a line coming from the fuel expansion tank. On a hot day, when the gas cap was removed, a blast of gas vapor would jump out of the tank.

The fix was to use an air pump and send a blast of air into each of the lines coming out of the overflow tank. All is OK now.

The 69 Euro has the small tank on the right trunk wall but the same fix should work on the larger left wall tank of a later car.

Richard M, NYC
 

[Travis71280]

Thanks for the reply Richard. I did try to blow the lines out with 135psi, the line on the driver side seems like it unclogged, but the other side didn't budge. Does anybody know if there is some kind of check valve in these lines somewhere inside the tank? I also tried to unclog it with bailing wire with no success. Also, didn't these cars at one point early on not have an expansion tank and just vented through the cap? Probably just going to hook the expansion tank to the gas tank again and see what happens.

[mdsalemi]

I had a similar problem years ago.  Lines were all clear.  Problem was in the tank.  New tank.  No problem, except an empty wallet.

[al_lieffring]

When ever someone puts up a post about fuel delivery problems, Michael will make his pitch for replacing the tank. Like almost everyone else who sees this I ignored it and for a year did everything imaginable to avoid  replacing the tank. When I finaly plunked down the bucks for a new tank, like magic my car became a reliable road worthy vehicle that I would not hesitate to take out on the road any where.
Thanks Michael.

[mdsalemi]

...and the funny thing was, I went to a local mechanic here, Karl-Heinz Autocenter.  Karl-Heinz apprenticed as a young man on the W113 assembly line in Germany.

When I began to describe the myriad number of symptoms to my problem (which the pressure buildup was but one), Karl-Heinz simply cut me off and said "it's your vuel tank."  Vee change your vuel tank and zee problems vill go avay.  I garantee it".  Lo and behold.

He then showed me a pile of old W113 fuel tanks he had replaced in the past year--all local cars all with similar issues.  These tanks do NOT last forever, and when you've done the obvious (blowing out lines etc.) it can be time to face reality.

[Travis71280]

Thanks everyone for the replies. Well thats not good news for someone on a college student budget.

[hauser]

Mike, did you go with an OEM or repro tank?

[mdsalemi]

Thanks, Al Lieffring, for the kind words if not sage advice.

It is astounding (perhaps it should NOT be) how often the same problems show up, and the answer seems to the same solution!  I certainly do not recommend willy-nilly changing a tank, but blowing out fuel lines and checking pump pressure etc. are all relatively easy to do and in my case had been done.  More than once.  In addition to the tank pressure issue, mine started misfiring below 1/3 tank.  Obviously fuel related as the new tank solved it all.

Hauser, at the time I needed the tank, I had to go with OEM, for 2 reasons: first, K&K had not yet received their first shipment of repro tanks--they were "on the boat" here.  Second, the mechanic didn't generally use K&K as a source anyway.

I should note that the first batch of tanks were rejected by Tim Kidder of K&K, because of a fit issue with the filler neck.  That problem was corrected.  I spoke with Cheryl at K&K (the goddess of sheet metal ) last week and she tells me that they have repro tanks, large 280 SL versions only, and that they fit.  Former problem corrected.

So, it is a savings of a few hundred $$$.

[bogeyman]

Michael:
After replacing your tank, did you actually open it up to see what was really causing the symptoms?
Perhaps we could develop a way to diagnose problems that would be correctable without going for a full replacement.

[al_lieffring]

Do a search on "flower pot" you will find photos of cut open gas tanks,
but according to Niel Young, "Rust Never Sleeps"
I drained, washed, flushed, rinsed, blew,poked wires through the ports and scraped, over and over and over again, but the rust kept coming back plugging up the system again and again and again. Every 100 miles my fuel filter would be completly clogged with 1/2 inch of red rusty sediment in the bottom of the canister. I even drove around with a feul pressure guage hanging from my rear view mirror. When sitting still in the garage the fuel pump would run for hours and hold pressure, but out on the road it woudl drop down to about 3psi and stall after 20 mins of driving. I even swithced to breakerless ignition hoping this would help the stalling problem. I did modify my 230sl to use the larger tank. A simple matter of making straps that relocate the fuel pump and gravel shield 1" forward of the original mounting.

[mdsalemi]

Mr. Karl-Heinz replaced the tank, (or one of his mechanics) not me personally.

He said (and this echoes Al's comments) that rust is there on an old tank.  EVEN IF you don't really see it, there are microscopic compromises of the interior surface of the tank.  Minute particles of rust form, and that's part of the problem.  The other problem also echoed by Al, is that 40+ years of sludge builds up in the flower pot.

So--

IF there were a way of properly disassembling the fuel tank, and
IF there were a way of properly re-galvaniziing or coating the interior, and
IF there were a way to remove, restore and renew the flower pot,
THEN we could properly repair an old tank.

But, as you can surmise, even if you could do all that, it is an awful lot of work that exceeds replacement cost.  I didn't like the cost of a new tank and I'm sure nobody else does...but after 40 years, it was time.

[hauser]

Mike, where does K&K have their tank made? 

How does the quality compare to OEM? 

Are there any visual differences between the two? 

Do you think that a K&K repro will last as long as an original???

What are the prices of the two?

[mdsalemi]

Re: K&K tanks et al.

Best to speak with K&K.  Talk with Tim or Cheryl.

Last week I made a post about the availability of quality sheet metal from them.  Someone sent me a PM saying that they think the sheet metal is made in Poland now and thus might not be as good as I alluded to or as Tim discussed at PUB 2007.  So, I called and spent about 20 minutes on the phone with Cheryl.  She had the answers (they make the 113 sheet metal in Michigan as described) and is a pleasure to speak with.  So, if anyone is considering a new gas tank from them--call them.  Hauser's questions are all real, and good ones and the best place to get an answer is from the source.  They will sell you both OEM or Repro and can tell you exactly what you get and are brutally honest.