Question: Where does the gas tank usually leak?

[The73vetteman]

Hello all,

I'm pretty sure I have a leaking gas tank. I say this because when it's full I get a strong smell of gas around the right rear wheel, but at half full the smell pretty much disappears, EXCEPT under sharp braking or acceleration.

So, this evening I removed the spare wheel carrier and started poking around with a mirror. As best I can tell the tank looks in pretty good shape, so can anyone tell me what kind of tell-tale signs I should be looking for?

Obviously, I don't want to replace the tank unless it's really necessary, so is there a way to verify that I have a leak (short of filling it up of course)?

Thanks in advance,

John

 

[SVO]

On your L48 gas tank, you have basically 2 vent lines and a gas supply line, all which have rubber hose connections. One of the rubber vent hoses could have aged and cracked, giving you the gas smell. Also, on the LH side tank vent, you have a separator valve, a plastic check valve type assembly, which could be cracked with age. Since you don't mention seeing any gas leakage, I would assume that the rubber connection from the tank sending unit to the frame rail fuel line is o.k., but doesn't hurt to check. I have seen a couple of cases where the metal connection at the fuel meter has rusted and is leaking just enough to be moist, giving you gas vapors. Also, you have a gasket at the fuel meter which could be weeping gas. Another possible leak point is the filler neck. The filler neck gasket could be bad or the filler neck itself may have a rust hole in it. To check the filler neck, you will need to check behind the filler neck rubber seal.The filler neck rubber seal is the rubber piece you see when you flip up the gas cap door and look down on the gas cap. Check all the rubber hoses in the fuel and vapor lines, and you probably will find your problem. Also, you may want to have your gas cap pressure checked to make sure that it is sealing properly and not the source of your fumes. HTH

 

[White75]

As SVO said, check and replace your rubber lines. My 75 did that and the lines were shot.

 

[herminator]

On your L48 gas tank, you have basically 2 vent lines and a gas supply line, all which have rubber hose connections. One of the rubber vent hoses could have aged and cracked, giving you the gas smell. Also, on the LH side tank vent, you have a separator valve, a plastic check valve type assembly, which could be cracked with age. Since you don't mention seeing any gas leakage, I would assume that the rubber connection from the tank sending unit to the frame rail fuel line is o.k., but doesn't hurt to check. I have seen a couple of cases where the metal connection at the fuel meter has rusted and is leaking just enough to be moist, giving you gas vapors. Also, you have a gasket at the fuel meter which could be weeping gas. Another possible leak point is the filler neck. The filler neck gasket could be bad or the filler neck itself may have a rust hole in it. To check the filler neck, you will need to check behind the filler neck rubber seal.The filler neck rubber seal is the rubber piece you see when you flip up the gas cap door and look down on the gas cap. Check all the rubber hoses in the fuel and vapor lines, and you probably will find your problem. Also, you may want to have your gas cap pressure checked to make sure that it is sealing properly and not the source of your fumes. HTH

These are good ideas. I just R&R'd my '73 tank and am intimately familiar with the items mentioned. Do you know where your overflow tube is routed? IF your cap leaks when full, could be coming out that tube onto the ground which would give you the odor without evidence of a leak. My advice, take the plunge, R&R the tank and replace all the hoses. Could prevent an unhappy event, that much gas smell while operating scares me.

 

[The73vetteman]

Just wanted to say thanks for the well-reasoned and well-explained replies. You've given me a few things to check.

I did notice some staining on the top side of the spare wheel carrier, which I'm thinking is due to gas. I've also seen what appear to be damp patches in the felt that separates the tank from the supporting strut - pretty much around where the ends of the retaining straps press against the tank. This has me wondering if the strap ends might be fretting against the tank and creating pinhole leaks.

Any comments on this hypothesis?

BTW, I'm definitely leaning towards just replacing the tank and hoses. Better safe than sorry, IMHO!

 

[herminator]

Just wanted to say thanks for the well-reasoned and well-explained replies. You've given me a few things to check.

I did notice some staining on the top side of the spare wheel carrier, which I'm thinking is due to gas. I've also seen what appear to be damp patches in the felt that separates the tank from the supporting strut - pretty much around where the ends of the retaining straps press against the tank. This has me wondering if the strap ends might be fretting against the tank and creating pinhole leaks.

Any comments on this hypothesis?

BTW, I'm definitely leaning towards just replacing the tank and hoses. Better safe than sorry, IMHO!

I had some of those same symptoms when I pulled mine. Found it was just old staining so cleaned everything up and reinstalled. With your fuel smell, you will kill 2 birds with one stone. BTW, replacement tanks are $200.00, good luck.

 

[White75]

Just wanted to say thanks for the well-reasoned and well-explained replies. You've given me a few things to check.

I did notice some staining on the top side of the spare wheel carrier, which I'm thinking is due to gas. I've also seen what appear to be damp patches in the felt that separates the tank from the supporting strut - pretty much around where the ends of the retaining straps press against the tank. This has me wondering if the strap ends might be fretting against the tank and creating pinhole leaks.

Any comments on this hypothesis?

BTW, I'm definitely leaning towards just replacing the tank and hoses. Better safe than sorry, IMHO!

mine did that. the top hose was leaking, the gas was then running down the retention straps. Dropping the tank is not hard so it is worth it if you have the time and want piece of mind. drain as much of the tank as possible first though. If you want to check for leaks around the lines, pull the passenger tail lights off and look through the holes. crank the engine for 30 seconds or so and if you have leaky lines you should see some gas from the lines. the ones on top are harder to see but if you remove the rubber from around the fuel door opening (it is missing on my 75) you can see the lines if you look with a flashlight.
Again, it may be easier to drop the tank if you want to be 100% sure

 

[herminator]

BTW, be careful cleaning up the tank if using sandpaper or a wire brush as fumes are combustable. To mt completely, the trick I learned was using a large rag or small towel as a wick to get the last of the fuel out.

Another trick for reinstall was, I made a t handle with a hook and raised/held the tank in place by the fuel neck with an engine hoist to hold it while I put the cross support back in. The straps are a b**** but the key there is to loosen (not release!) them on the adjustors near the bumper mounts.