MGB Gas Tanks | Bradley Restoration

That Old-World Finish

Sun, 19 Oct 2008 17:13:40 -0700

Luckily, sitting and meditating on the vagaries of old cars gave the pump enough time to cool down, and some fuel to dribble into the vacuum. Turning the key back on after good rant would allow the pump to blup enough fuel into the carbs to limp home.

Turns out, the tank had run dry years ago and the fuel, combined with whatever fuel additives were in there, had turned into one of the finest varnishes imaginable. The still-liquid gas was several years old, having been added long after the damage was done, put there specifically to fool a gullible MG technician into thinking that the tank was good. You can see the high-tide line of what was about 9 gallons of fuel. Imagine those 9 gallons, evaporated and concentrated into a last gallon or so of muck at the bottom of the tank, and you can understand why the blocked pickup screen was the culprit.

You can just assume that a 40-something-year-old gas tank is going to need to be replaced. MGB tanks rust out from the top due to trapped water around the filler neck. They can also rust out from the inside, from condensation and moisture absorbed into alcohol-laden fuels. I even had one where the tube itself had a rusted hole about halfway up. The car would run fine until it reached half a tank, and than fall on its face as the pump lost siphon and just sucked air.

Update!!! OK, after three of them all in this last year, I am officially recommending that everyone who still has an original tank just roll over and buy a new one. Three cars have come in, all with good original tanks, that would not supply fuel in any reliable quantity. Blame whatever long-chain molecule you may like, but the screens themselves were no longer pervious to fuel. These were clean, non-rusty, no chemical additives or preservatives, good tanks! But something in modern gas is attacking the plastic mesh of the pickup screens and causing them to swell and restrict fuel. Replacement tanks have a much larger mesh pickup screen and seem to behave much better with modern gas. I don't like it any more than you do. We can count ourselves lucky that at least we have reasonably priced replacement tanks available for the asking.

The 10¢ Solution

Sun, 19 Oct 2008 16:56:16 -0700

The red plastic sleeve has a shoulder near the lower end. When it is assembled, the pickup tube is held suspended about 3/8" above the bottom of the tank.

You can see from the glossy red varnish that this screen is barely permeable. When clean, the screen will be a white, woven material. This one would flow enough fuel to idle the car, and even rev it up under load. But, try to go for a drive, and it would still only supply enough fuel to idle. The pump starved for fuel, started to pull a vacuum and heated up until it stalled.

What is probably a dime's worth of parts, deep in the inside of the tank is responsible for having to replace the entire tank. I don't mind replacing a rusted out tank, but it hurts when the tank appears to be in good shape and shows no sign of rot.

Lift and Separate...

Sun, 19 Oct 2008 16:53:45 -0700

Pulling up on the tube allows the screen to be removed.

(You can also reverse-engineer how the tanks were assembled. The builder would bend the outlet fitting up while pushing the tube down into the screen. Then, when the tension was taken off of the fitting, the tube would spring down, holding the screen in place.)

You can pick me up anytime!

Sun, 19 Oct 2008 16:51:53 -0700

Here is a close-up of the plastic screen at the end of the pickup, held in place by the pickup tube and the little sheet metal tab.

Hats off, please...

Sun, 19 Oct 2008 16:33:02 -0700

Working with fuel tanks can be extremely hazardous! Only attempt such work if you know what you are doing, and at your own risk! Don't come to me if you kill yourself to death! You have been warned!

We filled the tank to the brim with water, to eliminate any chance of combustible vapor. Using a plasma cutter, I zipped the top of the tank off, to show how the inside of a B tank is constructed.

You can see on this original tank, the two baffles welded to the lower half of the tank, and the pickup tube on the right. The sending unit is frozen in place.