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MG TD TF 1500 - The gas tank leak that won't go away...

OK, I'm completely stumped on this one. I've had the TF about two months now, and when I first got it I overfilled the tank and had bad sloshing issues. Drove the tank down to the point where that wasn't an issue anymore, and I still came home with a wet splash apron. It didn't leak sitting still--only after a drive.

The fuel sending gauge was stuck when I got the car, so I took the tank off last weekend to fix--and inspected the tank thorougly for any other places it might be leaking. Nothing. Put it all back together, ran errands all last Monday, not a drop of gas on the apron at any stop. Until I went up my driveway--which is about a 15% grade. Then, wet apron (on the driver's side). And while I did have a fullish tank of gas, I am 100% certain it is not sloshing out of the filler cap--everything up there was bone dry.

Same story yesterday. Errands around town, no leak. Up my driveway, leak.

All seals new. All fittings new. Cap not leaking. But up a hill = wet splash apron. Thoughts?

Andy
TF0537
A.T. White

Andy,
I'm sure by now that you've seen the archives concerning the solution for gasoline sloshing out the top of the filler neck. Two fixes for this problem are to inspect and then replace the gasket (if necessary) on the filler cap.

The second is to take an ordinary brass sink drain tube, the ones found in your local hardware store and about 4 to 6 inches long, and drive it into the filler opening using a block of wood and a mallet, until its fully seated. They are a perfect fit, although just a bit on the tight side. The theory here is that the gasoline won't be able to slosh up the length of the tube when you are cornering or going up or down grades. You best check the archives on this, as I believe some have suggested an eighth inch hole be drilled through the side of the tube prior to inserting it into the filler opening. Perhaps someone will hop in on this point to clarify.

Your situation sounds suspiciously like the gas is coming out the filler cap, even though you see no such evidence, except for what you find on the apron. Good luck!

Gene
P Burgess

How close to the top is "fullish'? George
George Butz

Would jacking up the front of the car (ramps?) to simulate the 15% grade of you driveway make sense?
Sounds like gasket on filler cap in not sealing.
Cheers,
David 55 TF1500 #7427
David Sheward

OK, nobody believes that it's not sloshing out of the top except me. My dad gave me a thirty minute lecture last Monday on how it had to be sloshing out of the top. My mechanic gave me the same speech. Nobody here believes me either. So here's what I just did. I got a heavy duty balloon--remember the ones you tie a rubber band to and punch, one of those--and inserted it through the cap so that most of it was inside the tank, and inflated it some. Then I taped paper towels all around the filler cap.

Drove it around the block a few times. Stopped at the pool and gave the back half of the car a good eyeball and sniff test. No gas. Then up the driveway. Gas. The neck of the filler is completely sealed by the balloon, the paper towels are completely dry, yet there is gas on the splash apron. So it's gotta be the bottom of the tank somehow. Except that all the seals and fittings are brand spanking new. And the fact that it's only an incline that causes the problem. And, I should add, only when I'm going uphill. Because when I go down the driveway I'm fine.

So my current half-assed what-the-hell theory is that there's a weak seam, and the extra pressure on it going uphill is opening it up some. But it's a weak theory...

Andy
TF0537

A.T. White

Any possibility the fuel is leaking somewhere forward of the tank and, when the front is elevated, the fuel runs rearward along the fuel line, making its way onto the splash apron?

You should be able to test this by elevating the front of the car using a ramp or jack stands and noting the behavior with the engine running.

Perhaps the problem is not being observed at other times because the fuel drips on the ground or evaporates while at speed.

Larry
Larry Shoer

Larry,

I like your idea a lot. First chance I get I'll put her up on the jackstands.

Regards,
Andy
TF0537
A.T. White

Andy - It sounds like you have a leak somewhere along one of the end welds of the tank or along the fuel line as Larry suggests (although as I remember, the fuel line is below the level of the tank but it wouldn't hurt to check this out). You can also remove the end panels from the tank in situ and check for any wetness around them. Cheers - Dave

PS. that was a good though to use the ballon to seal the tank filler neck as a check on that.
David DuBois

Oops, I meant to say that the fuel line is below the level of the rear splash apron. Cheers - Dave
David DuBois

Andy,
Go back and tape some paper towels under the tank and fuel level sending unit(Very good Idea by the way) Now, how about this thery,,,,, gas is leaking from your newly fixed sending unit with new seals etc.,,,, when the car is on the level, it will drip down onto the ground,,,, but when the car is heading uphill, the angle makes the leaking gas drip onto the tank and then it follows the tank untill it drips onto the apron,,,

SPW
Steve Wincze

If you drove it very far with the tank inlet sealed by the balloon, there has to be a leak at a seam or somewhere as the this is a vented tank system, and would not run far with no air.

Dallas
D C Congleton

Andy,
You must have a leak somewhere. The fuel system is "vented" ...if you were "air-tight" with the "balloon seal" it would have stopped running.
(Found that out when I sealed my neck a little too good trying to get it from sloshing out the cap years ago!) Take the acorn nuts off the side panels...jack her up to simulate your driveway grade and see where your paper towels get wet first.
One bit of caution using the "plumbing drain fix" ...on my car I had to grind off about 2cm to get the cap to close. (of course this was done off the car... sparks and fuel vapors not a good thing...LOL)
Best of luck & let us know when you find it!
Cheers,
David
David Sheward

Another possibility is a wear point under the straps that hold the spare tire carrier.

Dallas
D C Congleton

Dallas may be on to something. When doing the TF there was some surface corrosion in that area under the rubber. All it take is a pin hole. Could be high and running down behind the strap and onto the rear apron.

Dan H.
Dan Hanson

Good point Dallas ....
maybe take straps and side panels off before jacking her up. It's only a few bolts!
David
David Sheward

If there is a pinhole in a seam, maybe with the chassis flexing going uphill it leaks? I like Dave S's idea about removing the side panels and jacking up. You may have to remove the splash apron (not a big deal to do either), so you can really see the bottom and sides.George
George Butz

Why bother jacking it up? Just put it on the driveway where it leaks. Make sure the car is blocked securly first.
Steve Wincze

If you have read the previous threads about an "emergency" fuel pump- that is a hand bulb of some type and a plastic tube going to a plug in the tank inlet - this or some other means of applying a couple of psi to the tank should force gas out of the leak.

Dallas
D C Congleton

"If you drove it very far with the tank inlet sealed by the balloon, there has to be a leak at a seam or somewhere as the this is a vented tank system, and would not run far with no air."

Not necessarily true, the balloon will expand as a vacuum is drawn so the fuel would have to be drawn down quite far before it would be cut off due to a vacuum being formed.

I like Steve's idea that the sending unit is leaking and on the steep driveway, the fuel is dripping onto the apron. Only thing wrong there, is that a leak around the sending unit would continue leaking while the car is parked and there would soon be a puddle of fuel under the car that would stink up the garage. Cheers - Dave
David DuBois

OK, first of all a confession: I am a big enough dumbass to create a vacuum inside a vented tank. "Damn, not hot enough for vapor lock" I thought. Took me about fifteen minutes by the side of the road to figure it out. Remove the balloon, idiot. A little reengineering involving a custom bent copper brake line solved that problem.

Next, the solution. Thanks to all the suggestions here I took off the side panel on the driver's side, covered everything with paper towels, drove up on the ramps...and found my leak. Got out the welding rig...no, not that much of a dumbass.

As an aside, my wife used to work for a little company called Snap Products (now owned by Pennzoil) whose big product was Fix-A-Flat. Right after she started working there a fellow got killed by welding on a rim with a tire full of Fix-A-Flat. At that time FAF had an explosive propellant, which obviously contributed to the accident. The company was held liable, paid out quite a lot of money, changed the formulation, and now every can has a "do not weld on a rim" warning logo on it.

Not to lessen the tragedy here, but who in their right mind would weld on a rim that had a fully inflated tire still on it?

Anyway, thanks all for the tips. Of course I would find the hole after I had the tank off a week ago. Guess what I'm doing this weekend?

Andy
TF0537
A.T. White

Andy,

Glad you found the leak. There may be other pinhole leaks ready to make their presence known. Although it is a fair amount of work, you may want to consider one of the chemical tank coatings that are designed to fill the pinholes and isolate the untreated interior metal walls from exposure to gas, air, and moisture.

I carefully researched the different coatings and used one that produced a near glass-like finish on the interior of the tank and is described as withstanding "modern ethanol fuels."

http://www.caswellplating.com/aids/epoxygas.htm

I'm going to get a reputation here, but I put together a detailed set of notes for doing this work. If you would like a copy, send me an e-mail message.

Larry
Larry Shoer

As a follow up on Larry's suggestion, it is of VERY important to use a product that is resistant to todays fuel formulation (and hopefully to any future formulations if that is possible). When I restored our TD nearly 30 years ago, I used the only available product at that time, which was aircraft slushing compound. It did a great job, but in recent years, it stated to dissolve and ultimately it glued the check valves in the fuel pump and the needle valves in the carburetor shut. I wound up having the tank dip stripped to get rid of all the old sealer and had the tank treated with a zinc phosphate treatment that is supposed to rust proof the tank (time will tell). Of course, all of this removed the paint from the outside of the tank and I had to get that redone also. I would suggest on an old tank that has some leaks showing up, that it be dipped (radiator shops can do this with stuff that spares the paint, but removes rust) to insure a completely clean tank and then follow up with the product that Larry suggests. After having the tank de-rusted and before sealing it, drop a small drop light into the tank, turn out the lights in the garage and look over the outside of the tank for any light leaks. It is a good idea to have a center punch and a hammer in hand so you can punch a dimple into the tank at each light leak, as you will not be able to find them once the lights are on. I did that on the final go around on my tank the first time I had it stripped and found three or four more holes than were evident with the light on. Since the tank had been dip stripped, I brazed the holes shut and didn't have any leaks when the tank was put back on the car.

Larry - Have you sent your various write ups to Bud for inclusion on his T Talk web site, or you could send them to me and I'll put them on my web site (although Bud seems to be much quicker about getting stuff on his web site than I am). Cheers - Dave
David DuBois

Larry... that is quite the website...looks like a number of interesting coatings.....
gblawson(gordon)

Here is another choice- very good product. Like all of these products, follow the directions precisely.

http://www.por15.com/FUEL-TANK-REPAIR-KIT/productinfo/FTRK/

no financial interest, but have success with this coating (so far) for 5 years using a methanol blend.
Dallas
D C Congleton

Dave,

Thanks for the reminder. I'll send the information to Bud for posting on www.ttalk.info.

Larry
Larry Shoer

Files received from Larry. I'll try to have them up tonight. Bud
Bud Krueger

See http://www.ttalk.info/ShoerTank.htm for Larry's info.

Bud
Bud Krueger

Told you that Bud was quicker about getting stuff on his web site, that would have taken me at least a week or a month. Cheers - Dave
David DuBois

This thread was discussed between 13/09/2009 and 16/09/2009

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