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MG MGB Technical - Problem with Replacement Fuel Tank

Since replacing it a year or two ago, my fuel tank has had an annyoing habit. If the car is pointing uphill for a long period of time and the tank is 1/4 full or less, it will run out of gas. Leveling the car will start the flow again.

The fuel pickup seems to be in place in its clip in the dimple in the bottom of the tank. Interesting that with enough fuel in the tank to have the entire plastic screen submerged, the pump wouldn't pick up fuel. I dropped the car down to nearly level and it made no difference. I disconnected the steel line from the flare fitting at the tank, and connected it to a hose into a jar of gas. The pump did pull fuel this way, so that seems to isolate the problem to the tank.

Having reconnected the tube, I blew through the supply line. Bubbles appeared at the end of the pickup. However, when I sucked on the hose, all I got were fumes. In fact, I had to put two gallons back in before the pump would draw fuel.

Could it be that there's a leak in the pickup tube inside the tank, just above the 1/4 full level? One that's small enough not to be able to vent the full pressure of my blowing, but large enough to supply the entire draw of the fuel pump (and test mouth)?

If anyone has some advice or an experience similar to this, I would be happy to hear it. The car is a '74 chrome bumper roadster, the tank was purchased 1.5 - 2 years ago and has no baffles to be seen from the sender hole. It does have the expansion tank in the center.

Many thanks,

Matt K.
Matt Kulka

Your symptoms sound something like what I call the "broken straw" syndrome. Usually I have seen this happen with rubber hoses which develop cracks/leaks along their lengths which go all the way through to the interior. Sometimes, this will happen around the circumfrence of a tube at a fitting or hose clamp. In essence, the tube leaks air and so sucks more air than fluid. Check to see if this is not true for your pickup tube.

For testing this hypothesis, you could, I suppose, rig up a length of small diameter tubing to go inside of the tank mounted pickup tubing all the way down to the dimple and filter screen. You would then have to hook up the small line to a suction device (large syringe would work, I think, and see if it works better than your pickup tube. If so, you might have to have the pickup tube fixed or replaced at a tank repair shop. Or pick up another tank, if available. Good luck!
Bob Muenchausen

Matt,
I too noticed a similiar problem with a replacement tank in my 67' GT. I was at a traffic light back in line pointing up a hill. The car acted as if it was running out of gas even though it had at least a half tank. Once I crawled to the top of the hill and leveled off, everything was fine. I am curious to see what everybody has to say.
Where did you buy your tank?

Steve
Steve Brooks

I have heard rumors that replacement tanks lack an original baffling system.

This *may* allow an uneven distribution of fuel. Do you notice if the petrol sloshes around? That may be an indicator.

I paid for a rather costly, (I thought) refurbishing of the original '64 tank -- cleaning and coating etc. and never hear fuel sloshing.

hth
glg

Bob,

I agree with you. I think there's a leak in the pipe. I like your test plan. I have some small clear tubing I had already been testing with, and will give it a go.

Since this is my daily driver, I wish I could fix it myself. If I could get inside the tank, I could slip a short piece of fuel line and clamps over the pipe, moving it up until it blocked the leak. But I can't get in there. You seem like a very inventive guy. Got any ideas on how to accomplish that? (Bear in mind I don't have welding skills, and probably wouldn't do so on a fuel tank anyway.)

Steve,

I got my tank at Brit-Tek. I'm sure they use the same supplier as the other mail order outfits. I'm planning to call them to see if they have any suggestions. I won't ask about them replacing the tank. I had the tank sitting in the garage about 6 months, then on the car for over a year. I think the warranty period is up by now.

glg,

Except for the 'drum' in the center, this tank is baffle free. However, in my testing I had the sender off, and was able to see that the fuel pickup screen was completely submerged througout testing, even with the left side of the car jacked up high.

My brother is restoring a '57 Rolls. Fuel tanks for those are harder to come by. He found a place that would sand blast it inside and out, then coat the inside for him. (I suppose any leftover media gets trapped in the coating.)

That seemed a bit much for my inexpensive little car, when replacement tanks can be bought easily. Perhaps in the long run you did the right thing. I wish I hadn't junked my old tank.

All,

Unless someone comes up with a good home remedy for the leaking tube I suppose I'll have to have it professionally repaired. I hate having only 7 useful gallons of capacity.


Tanks for the help,

Matt
Matt Kulka

Matt, Block off the original fuel outlet at the fuel tank and buy the later model tank sending unit with the integrated fuel pickup tube. Fits right in with no modifications at all.

Ken
Kenneth Meyers

Kenneth,

Clever! Does the newer sending unit work with the older guage?

Matt Kulka

Matt, Kenneth's idea seems like the first to try and probably the simplest fix!
Bob Muenchausen

Matt,

My out-look on life is to learn something new and have a good laugh every day -- otherwise it's a wasted day.

Thanks for the learning something part -- the good laugh is bound to turn up somewhere, sometime.


glg
glg

Later sender/pickup should work fine. I'm using one with my '75. I needed a 2nd fuel line into the tank for EFI.
Peter

The gauge and sender changed electrically during 1964 and the early and late are not compatible. The sender changed again later on to incorporate the pickup and these two *should* be compatible.
Paul Hunt

This thread was discussed between 03/09/2003 and 06/09/2003

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