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MG MGB Technical - Full Tank Vapors

Filled the 67 GT for a club trip. Topped it off and now I notice gas vapors in the garage. No leaks under the hood, around the gas cap or at the filler tube connector.

It could be from the vent, but it was suggested there could be pinholes in the top of the tank.

Tank is in very good condition, but was not removed when the car was restored in 2005.

Is the pinhole suggestion a valid potential? If so, dropping the tank would be prudent.

Will see if the vapors go away after I drive it down a bit.
Bruce Cunha

" it was suggested there could be pinholes in the top of the tank"

Very likely. Silt tends to get trapped between the tank and the boot floor, causing corrosion.

This is how mine looked...

Dave O'Neill 2

Yep, sorry Bruce, but the outside of the tank can look fine, while the top is perforated. As Dave said, the narrow gap between the tank and the floor traps damp and muck - perfect for rusting. If you can't find any other cause, you would be wise to drop the tank and check.
Mike Howlett

If the top is perforated and liquid fuel escaping when topped off it usually results in staining down the sides.

As a 67 it would have a ventilated fuel cap, and expansion in the tank can expel vapour. Also if completely filling a tank expansion can overflow from the filler cap, but that is usually visible on the bumper.
paulh4

Yes, mine (a 1969) vents through the cap and it can smell a bit if the tank is full and the weather is warm.
Mike Howlett

My 79 is getting a new tank soon. the tank is original, and as I rub my finger over a damp spot, the tank "weeps" fuel. For now, just keeping the tank around the 1/2 mark until the new tank arrives.

Cheers
Gary
79 MGB
gary hansen

Thanks all.

Well, I did find the problem. Came out this AM to get ready for a club trip and the garage reeked of gas. Had to put a fan in to ventilate it.

Backed the car out and immediately saw a puddle starting under the back passenger side. Got the flashlight and found fuel dripping out the steel fuel line to tank nut.

What surprised me was that nut was just not slightly loose. Probably two full turns to get it tight. Have not noted the gas smell until this fill up.

Just another reminder why going over things periodically to tighten them is a good idea.

Bruce Cunha

Bruce, Get some Waxoyle or similar squirted on top of the tank. I also seal up the forward gap between the tank and the boot floor. Often if the top of the tank goes porous the boot floor starts going too.
Allan Reeling

Excellent suggestion Allan. Car is due for a reapplication of waxoyle, so I will include the top of the gas tank. Thanks.

Bruce
Bruce Cunha

Wax Oyle, is he related to Olive Oyle? Her thick brother, perhaps.

paulh4

No Paul that would be Thickso Tropic!
Allan Reeling

This thread was discussed between 01/04/2017 and 03/04/2017

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