Leak or pressure testing a mid-year gas tank

[Gary B.]

I was recently given an original '67 gas tank by the owner of a local Corvette repair shop. The '67 in question had been sitting for years and the owner had the car's gas tank and all fuel lines and connectors (as well as brake lines and calipers) replaced with new components and he did this regardless of whether an item was leaking or not. He just wanted everything to be brand new and he's not an NCRS type, so wasn't concerned with originality (e.g., about 20% of the tank sticker was still attached, but the didn't want it).

The original gas tank looks to me to be in excellent shape inside and out, but I'd like to leak or pressure test the tank to make certain it doesn't have a leaky seam. Does anyone know of a simple technique to pressure test or leak test a tank that's out of the car? How about a pressurized air test? How much PSI should I use? Or are there speciality shops that will pressure test a gas tank for a fee?

Thanks,

Gary
Northern California Chapter
NCRS # 28818

[Larry M.]

Re: Leak or pressure testing a mid-year gas tank

Gary:

I would make a rubber gasket for the sending unit hole, and then put it on sawhorses and fill it with water.

If it doesn't leak water on the driveway, it should be okay for your car.

Drain and wipe dry when finished. If your arm/hand is too large to get in the gas filler hole, just throw in a small towel and move it around with a small stick or wire.

Larry

[Bill I.]

Re: Leak or pressure testing a mid-year gas tank

Sounds like a good idea, one word of caution, remember to hold on to the corner of the towel. Bill

[John H.]

Re: Leak or pressure testing a mid-year gas tank

In the plant, we capped the sending unit outlet, used a sealed O-ring adapter filler cap with an air fitting on it, dunked the tank in a tub of water that came up about an inch above the filler neck-to-tank joint with the tank submerged, and applied 2-3 psi of air. No bubbles was an OK unit. Tank came out of the tub, removed the caps, and it went on a slide rack to the line for installation.

[Gary B.]

Leak or pressure testing a mid-year gas tank

Sounds like it should hold 3 psi, say overnight, so long as I can seal off the sender and fill holes adequately.

Gary

[Dick W.]

Re: Leak or pressure testing a mid-year gas tank

Gary:

I would make a rubber gasket for the sending unit hole, and then put it on sawhorses and fill it with water.

If it doesn't leak water on the driveway, it should be okay for your car.

Drain and wipe dry when finished. If your arm/hand is too large to get in the gas filler hole, just throw in a small towel and move it around with a small stick or wire.

Larry

Air will leak where water will not. Air pressure, 2-3 psi as John stated, is the best way to test it. Submerge the tank in a tub of water, no bubbles, no leaks

[Jim T.]

Re: Leak or pressure testing a mid-year gas tank

I would not use water to fill the tank to test for leaks based on previous experience with a gas tank. Only liquid inside the tank I would use is the real thing, gasoline.

[Larry M.]

Re: Leak or pressure testing a mid-year gas tank

Air will leak where water will not. Air pressure, 2-3 psi as John stated, is the best way to test it. Submerge the tank in a tub of water, no bubbles, no leaks

Dick:

I agree with you or John.....as long as you have the correctly designed facilities for doing this check. I think this is how most radiators are leak checked.

The 1967 gas tank is a vented tank, so it runs no pressure. If you are not careful with adding air pressure it could result in a tank seam coming apart, you need to have a home pool (or equivalent) to submerge the entire 20 gallon tank, and once submerged it will take two persons (at least) to hold it underwater unless you weight it or tie it down.

Trying to do an air test and watching a pressure gage for leakdown will also likely result in frustration. I don't think Gerry can find two home-made seals that will fit that snugly and leak-free.

I mentioned the water as a humorous but practical way to do the leak check. The water will not hurt the inside of the tank, unless it is badly pitted or corroded. And in this case you don't want the tank anyway. To be safe, the tank should be filled with water anyway to displace any old gas residue and/or fumes. This has been SOP in the chemical plants for decades regarding washing and pressure testing used hydrocarbon equipment (plus we always used high purity nitrogen for the gas/leak testing).

As for me.....I would just buy a new Quanta tank. That's what I did just last month when I dropped the gas tank on my 1967 to do some work. Exact match, although a little more shiney due to the differences in the outer metal plating.

Larry

[Kenny C.]

Re: Leak or pressure testing a mid-year gas tank

If you want to test by filling with a liquid then do NOT use water. Water has a much higher surface tension than gasoline and will not show very small leaks like will become painfully evident with gas. For safety reasons you may not want to fill the tank with gasoline however diesel will work for the test and is safe and will drain out and clean without leaving water to corrode things. Believe me I learned this lesson many years ago when I used to paint motorcycle gas tanks and every now and again a perfectly nice paint job would turn to crap because of a tiny leak. And when your done with the diesel you can make some one happy with a free fill up in their truck.
Regards
Kenny

[William C.]

Re: Leak or pressure testing a mid-year gas tank

As an aside, many if not most old-time radiator repair shops can test (and repair) gas tanks.

[Gene M.]

Re: Leak or pressure testing a mid-year gas tank

Gary, you said the car had set for years. The inside of the tank can't look good. I would just get a new reproduction tank and end all issues and possible problems. The guy that replaced it originally had the right idea.

You can buy a brand new tank for about $160 delivered, no issues, clean, easy, done.