gas tank vent pukage when (over)full

[Stereolab42]

Filled up my gas tank (1970 Coronet) for the first time, got home... noticed a puddle under the car. Gas was basically squirting out of the candy-cane vent near the front of the tank. Opened the cap and was immediately showered with gas. I removed about a gallon with a manual pump and no more leakage.

I've read ALL of the threads on this topic and they all revolve around the two vent lines not being correct, venting properly, or so on. But I have a different theory about my situation. When I filled it up, it took about 20.5 gallons, and there was probably about a gallon in the tank (I deliberately drove it to near-empty to test the gauge). However, this tank looks like one of those typical aftermarket B-body tanks that are advertised as 19 gallons.

So I think the issue here is that it overfilled. I did not "top-off", but filled until the first click-off. My theory is that either because I'm running bigger wheels on the back or simply because of an incorrect install, my gas tank is lower in the front than in the back, which means gas will fill up to the fill pipe opening and leave no air in the rest of the tank for expansion and venting.

I went under the car and used a level to see if the "side seam" of the tank is angled up toward the back. Indeed it is, by quite a bit:

It should be level, no? If so, what's the easiest way to correct this?

 

[Dennis H]

Was the nose down at all when first parked? Is the vent loop just shy of contact with the rear shelf. Is it a vented cap.

 

[Stereolab42]

Was the nose down at all when first parked? Is the vent loop just shy of contact with the rear shelf. Is it a vented cap.

It was parked in my garage, which is pretty level. I'm not sure what you mean by rear shelf... the candy-cane loop, at least the part outside the tank, has good clearance it seems. The cap is actually vented, which I know is technically incorrect for 1970 (but surely a non-vented cap would just make the problem worse? Fuel wasn't leaking from the cap, it only erupted once I removed it.)

 

[Dennis H]

Got it. The vent inside the trunk that takes a high u turn needs to be real high very close o reaching the elevation to the elevation of the shelf bottom. Maybe you just had a fluke of conditions.i have a vented cap.

 

[69L48Z27]

Sounds like the fuel and tank expanded due to temp change from fuel coming out of the ground. Add that to a very full tank and it will spill over. If you got a shower that means there was some sort of pressure.

I don’t know how to fix it other than don’t fill it as full next time.

 

[Stereolab42]

Sounds like the fuel and tank expanded due to temp change from fuel coming out of the ground. Add that to a very full tank and it will spill over. If you got a shower that means there was some sort of pressure.

I don’t know how to fix it other than don’t fill it as full next time.

Some people on some threads say the same thing, that today's gas expands more so just don't fill it all the way. But I don't want to give up that easily. I am bothered by the fact that a supposed 19-gallon tank filled to 21-22 gallons. That's what still leads me to think that my tank is too much nose-down, which would let it hold more gas before triggering the shut-off mechanism in the handle.

 

[dadsbee]

.. or your gas station is ripping your off with an uncalibrated pump!

 

[Dennis H]

I’ve never filled the Coronet that I didn’t spill gas. I have a custom 23 gallon now, so I shut off early now based on sound.

 

[Stereolab42]

I've found out more. My car began life as a California car with the ECS (Evaporation Control System) crap. This involves use of four special vent lines, a special fuel tank, and other stuff. It was over-complicated and never worked very well, so when restored the PO just threw in a normal fuel tank with normal vent lines. (I can see the old ECS four vent lines still poking out from under my trunk, capped off.) Why does this matter? When reading the service manual, this caught my eye:

"The possible expansion of fuel in a full fuel tank,
due to a rise in temperature, is allowed for by a 1.4
gallon over-fill limiter tank inside the main fuel tank
which fills much slower than the main tank. When the
main tank is filled, it remains essentially empty to
allow for thermal expansion. (Fig. 1)."

I'm betting if I can find a tank with such a limiter tank inside it, my overfill problem will be solved. I looked at YearOne and CI and they both sell ECS tanks, but it's not clear if they are correctly reproduced to the point where they have this internal tank. Since adding something like that would require a bunch of extra careful welding, it should be reflected in a higher price, but the ECS and non-ECS tank prices are the same, so I'm guessing no. Plus if I installed an ECS tank but didn't want to use the ECS system per-se I'd have to shade-tree a new venting setup, since the ECS tanks have four vent nipples exiting the side instead of the normal two at the back.

Maybe I can pay for a custom tank to be built with such a limiter inside? (If anyone here has had custom fuel tanks built and can give a recommendation drop me a line.)

 

[Stereolab42]

Just called YearOne, the guy was able to physically look inside one of their ECS tanks for me, and as I feared the repro does NOT have an internal limiter tank.

 

[69L48Z27]

Call Quanta, if there is such a thing available today they would either have it or maybe know where to get it.

http://www.gastanks.com/