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Expanding fuel – spilling out of filler neck #2723119
12/10/19 11:09 PM
12/10/19 11:09 PM
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Clinton, NJ
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I don’t get it. I filled up my ‘68 GTS about 3 weeks ago. The usual, filled at the same station as always, stopped at the first hint of a click. Drove about 2 miles home, added stabilizer in ratio for new fuel added, car idled a while and I moved the car around the driveway and parked.

Today the outdoor temp jumped to near 60F in NJ. Has been in the 30-40F range for a while and was around 45F when I filled it up. I went in the garage the car is stored in, which is a single car, uninsulated garage and smelt gas odor. Figured out it was coming from my GTS and opened the gas cap (correct NOS chrome cap). Gas came pouring out and down the quarter. I freaked out and got some water and cloths to clean and I could see the side stripe getting melted. Could also see gas was behind the stripe so I peeled it off pretty far. Cleaned with water and some 3M adhesive remover to get any residue off.

The paint is damaged a little, it deformed around the stripe. Luckily it did not peel. Looked under the car at the neck to see if the donut was leaking and it was not. I did see that the frame rail was wet with fuel coming out of a hole in the metal, which means the gas was pushed down the neck vent and into the frame rail where it dumps.

I looked down the filler neck and can see gas at the level of the baffle inside. Honestly never looked in the neck before to see where it is when the gas pump clicks off. Gas can expand that much to rise up the neck and push out the cap with such volume? It was my usual 93 octane E10 junk they force us to buy in NJ. I cant get ethanol free. Does the ethanol expand more than regular gasoline?

Has to be one of the lowest points for me. Just finished this car in the spring after so many, too many, years on this project.

damage2.jpg
Re: Expanding fuel – spilling out of filler neck [Re: njmopar] #2723131
12/10/19 11:41 PM
12/10/19 11:41 PM
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Rogue River, OR
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Absolutely. If i filled my 70 w100 up at 5am and we had a 40 deg temp swing it would expand and run down the filler neck onto the cab.



Re: Expanding fuel – spilling out of filler neck [Re: Jeremiah] #2723153
12/11/19 06:18 AM
12/11/19 06:18 AM
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Holland MI Ottawa
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You have my sympathy. What an AWEFULL thing to happen. I cringed when you mentioned damage to the paint and stripe. Ugh.


Keep old mopars alive.
Re: Expanding fuel – spilling out of filler neck [Re: 2boltmain] #2723156
12/11/19 06:30 AM
12/11/19 06:30 AM
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Need to figure out why your tank vent isn't venting. My 51 does this as well. It's vented thru the cap, new cap still does it. Gonna have to add another vent to it.

Re: Expanding fuel – spilling out of filler neck [Re: Sniper] #2723165
12/11/19 08:10 AM
12/11/19 08:10 AM
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Tulsa OK
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The tank vent working or not wouldn't keep the fuel from spilling out. My tank vent works well on my car and I have had this happen before. My solution is don't store it with the tank 100% full, leave a few gallons out.


68 Barracuda Formula S 340
Re: Expanding fuel – spilling out of filler neck [Re: Bad340fish] #2723168
12/11/19 08:31 AM
12/11/19 08:31 AM
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What do you think is pushing the gas out?

Pressure

What do you think the vent is suppose to deal with

Pressure.

Seems to me your vent isn't working.

Re: Expanding fuel – spilling out of filler neck [Re: Sniper] #2723171
12/11/19 08:43 AM
12/11/19 08:43 AM
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Clinton, NJ
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In thinking about this overnight, I think the issue is pure fuel expansion and not the vent. The only vent on a 68 is located at the top of the filler neck, thats it. So while it may handle fumes that rise, if the fuel itself rises up, it serves no purpose. The vent was "working" as there was fuel in the frame rail where the line dumps out fumes. It just could not handle liquid.

I just cant imagine fuel expanding that much in ~20 degrees change to rise up the length of the filler neck and also into and out of the vent. In all my years of owning cars (a-body and others), this has never occurred.

Think about gas cans you have that sit in the hot sun. You open them, get the purge of fumes and maybe some liquid that burps out and thats it. Never overflows out like a waterfall.

Baffled on how much this fuel expanded. Given that I can still see fuel in the neck, guess I will be running that down or siphoning out.

Re: Expanding fuel – spilling out of filler neck [Re: njmopar] #2723172
12/11/19 09:01 AM
12/11/19 09:01 AM
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Tulsa OK
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Mine happened on a super hot day, I filled up, drove a couple of miles and when I got home the cap was whistling, opened it up and it barfed a good amount of fuel. It was 105* out.

The orifice in the vent line is very small, I don't think that is the problem here but I cut the end off of mine because I wanted to ensure it flowed enough air.

It may also be possible that when the tank is totally full the filler neck is submerged in fuel, any expansion that happens pushes the fuel up the neck. In that case you have the fuel expansion to deal with, and the trapped air above the fuel(above the filler neck) the factory vent location can't do any good there.

Last edited by Bad340fish; 12/11/19 09:07 AM.

68 Barracuda Formula S 340
Re: Expanding fuel – spilling out of filler neck [Re: njmopar] #2723188
12/11/19 09:47 AM
12/11/19 09:47 AM
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Clinton, NJ
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So some searching for a calculation for gasoline expansion. The formula is ΔV = V0βΔT
where is β the volumetric thermal expansion coefficient. For gasoline (does not say ethanol content) is 0.00095 1/degree C or 0.00053 1/degree F.
So for an 18 gallon tank and a 20F temp increase, the volume change is:
ΔV = 18 * 0.00053 * 20
ΔV = 0.1908 Gal

More than I would have expected and wondering if ethanol changes this as well. Need to measure the filler neck to see the volume of that cylinder.

Doesn't fix my problem, but if I can put some reasoning behind this, makes me feel better.

Re: Expanding fuel – spilling out of filler neck [Re: njmopar] #2723200
12/11/19 10:43 AM
12/11/19 10:43 AM
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St. Charles, MO
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Had this issue with my road runner, which was made worse by the low location of the filler behind the rear licence plate.

I just had to change my driving habits and stop filling up the tank to the top at the end of a cruise right before I put it in the garage.

Sorry about your trouble.

Re: Expanding fuel – spilling out of filler neck [Re: njmopar] #2723219
12/11/19 12:34 PM
12/11/19 12:34 PM
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East Aurora (Buffalo) NY
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Originally Posted by njmopar
So some searching for a calculation for gasoline expansion. The formula is ΔV = V0βΔT
where is β the volumetric thermal expansion coefficient. For gasoline (does not say ethanol content) is 0.00095 1/degree C or 0.00053 1/degree F.
So for an 18 gallon tank and a 20F temp increase, the volume change is:
ΔV = 18 * 0.00053 * 20
ΔV = 0.1908 Gal

More than I would have expected and wondering if ethanol changes this as well. Need to measure the filler neck to see the volume of that cylinder.

Doesn't fix my problem, but if I can put some reasoning behind this, makes me feel better.


I don't know a-bodies a whole lot, so guessing on dimensions of filler tube. But this could be possible. Assuming 2" tube about 2' long, I get a volume of about .32 gal. So if expansion is 0.19 gallon, then the tube only needs to be about two thirds full before expansion pushes it out. If tube is shorter then, even less holdup in tube is available.

Now, the issue is that when topping off, we all have a habit of clicking the handle a few times. If one just stops when the first automatic stop hits, then you shouldn't be over filling tank. The hose mechanism has a pretty low delta P drop sensor that clicks off the flow. So once fuel starts holding up in tube due tank level being high, it should click. At first click, there should be enough residual room in the tank to allow tube to drain down. Then you have plenty of buffer for expansion.

I know what you are thinking; "I always stop on one click". Well, have someone watch you. You'd be surprised how much people do this subconsciously. I had to teach this to myself to stop this practice when getting gas. Plus I always get gas before I head out, not when coming home. Then I am sure to use some. At 9-10 miles to the gallon, it doesn't take a long ride to make some room in the tank. drive


68 Road Runner (383/4speed, post car w/decor pkg)
69 Road Runner w/472 Hemi & 4 speed.
70 Challenger R/T SE EF8 w/ V9J, U - A32 - Major Project
Re: Expanding fuel – spilling out of filler neck [Re: RoadRunner] #2723223
12/11/19 12:45 PM
12/11/19 12:45 PM
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Hamtramck, PA
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This is a common problem.

Fuel is stored underground where it can be much cooler than outside temps or temperatures inside heated garages.

If you have ever filled a 100 gallon diesel tank in the middle of winter right before parking in a warm shop for the night...... well, it makes a big mess.

The closest non-ethanol place to me is about 9 miles away, so I never, ever 'top up' & the drive home lowers the tank volume enough that thermal expansion is not an issue for me.

Re: Expanding fuel – spilling out of filler neck [Re: Alaskan_TA] #2723227
12/11/19 01:06 PM
12/11/19 01:06 PM
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Back in the day, it was common to see A-bodies with fuel stains below their filler nicks, sometimes pretty big stains.
On mine, I was always worried about that and never filled them up; ran them maybe 7/8 full max.

I've also seen hundreds of 68-70 B-bodies with fuel stains on the rear bumpers/license brackets, but at least that doesn't affect paint.

Re: Expanding fuel – spilling out of filler neck [Re: njmopar] #2723230
12/11/19 01:19 PM
12/11/19 01:19 PM
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central il.
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Sorry for your misfortune.

Anyone who's every had a motor cycle when they were young probably found this out the hard way I sure did. I had just filled up my KZ 900 with gas on a hot day and as I was driving the heat got to the fuel that was so much cooler from being in a storage tank and it started blowing out the gas cap all over me & the bike. Nothing like having gas blown in your face on a hot day. Heck I've even had this happen on a lawnmower.

The one that surprised me most was I had a friend who had a paint shop and he had the garage door open and the sun came in and shinned on the gas fill on a nova he just painted and the vapors melted the fresh paint. He said he also had it happen with a can of gas sitting too close to the car in hot weather.

Re: Expanding fuel – spilling out of filler neck [Re: njmopar] #2723231
12/11/19 01:19 PM
12/11/19 01:19 PM
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Originally Posted by njmopar
So some searching for a calculation for gasoline expansion. The formula is ΔV = V0βΔT
where is β the volumetric thermal expansion coefficient. For gasoline (does not say ethanol content) is 0.00095 1/degree C or 0.00053 1/degree F.
So for an 18 gallon tank and a 20F temp increase, the volume change is:
ΔV = 18 * 0.00053 * 20
ΔV = 0.1908 Gal

More than I would have expected and wondering if ethanol changes this as well. Need to measure the filler neck to see the volume of that cylinder.

Doesn't fix my problem, but if I can put some reasoning behind this, makes me feel better.


ethanol is .00061
10 percent ethanol if I follow your math would be 1.8 gallons of the stuff.
16.2 gallons of gas
total expansion following the same formulas would then be. .19366 vs .1908
so ethanol free still wouldn't save you. though I am surprised how much that little ethanol changes it.

Re: Expanding fuel – spilling out of filler neck [Re: Andrewh] #2723242
12/11/19 01:40 PM
12/11/19 01:40 PM
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State of Jefferson
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I'm also surprised by how much the volume can change. shock

In my truck (tank in the cab), just going around a corner or coming to a stop is enough to lose a little when it's full eyes

Good thing I only need to fill it half a dozen times a year laugh2


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Re: Expanding fuel – spilling out of filler neck [Re: njmopar] #2723256
12/11/19 03:09 PM
12/11/19 03:09 PM
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Rio Linda, CA
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That's why a thermal expansion tank was added to the system starting around '70.


I'm supposed to respect my elders, but its getting harder and harder for me to find one now.
Re: Expanding fuel – spilling out of filler neck [Re: njmopar] #2723260
12/11/19 03:28 PM
12/11/19 03:28 PM
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Clinton, NJ
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Performance Car Graphics is doing me a solid and selling me just the 1/4 stripe, so I dont have to get an entire kit again.
Hopefully the LAST time I have to install a stripe on this car.

Re: Expanding fuel – spilling out of filler neck [Re: njmopar] #2723280
12/11/19 04:48 PM
12/11/19 04:48 PM
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St. Louis, Mo
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Originally Posted by njmopar
I don’t get it. I filled up my ‘68 GTS about 3 weeks ago. The usual, filled at the same station as always, stopped at the first hint of a click. Drove about 2 miles home, added stabilizer in ratio for new fuel added, car idled a while and I moved the car around the driveway and parked.

Today the outdoor temp jumped to near 60F in NJ. Has been in the 30-40F range for a while and was around 45F when I filled it up. I went in the garage the car is stored in, which is a single car, uninsulated garage and smelt gas odor. Figured out it was coming from my GTS and opened the gas cap (correct NOS chrome cap). Gas came pouring out and down the quarter. I freaked out and got some water and cloths to clean and I could see the side stripe getting melted. Could also see gas was behind the stripe so I peeled it off pretty far. Cleaned with water and some 3M adhesive remover to get any residue off.

The paint is damaged a little, it deformed around the stripe. Luckily it did not peel. Looked under the car at the neck to see if the donut was leaking and it was not. I did see that the frame rail was wet with fuel coming out of a hole in the metal, which means the gas was pushed down the neck vent and into the frame rail where it dumps.

I looked down the filler neck and can see gas at the level of the baffle inside. Honestly never looked in the neck before to see where it is when the gas pump clicks off. Gas can expand that much to rise up the neck and push out the cap with such volume? It was my usual 93 octane E10 junk they force us to buy in NJ. I cant get ethanol free. Does the ethanol expand more than regular gasoline?
Has to be one of the lowest points for me. Just finished this car in the spring after so many, too many, years on this project.


I had the same thing happen about 4 years ago on my 73 Challenger. It was Thanksgiving night. I walked into my garage and smelled gas. It had run down my quarter panel and turned my shiny red paint to jelly. All I can figure is that I didn't have the gas cap tightly sealed.

Re: Expanding fuel – spilling out of filler neck [Re: 318 Stroker] #2724247
12/15/19 05:53 PM
12/15/19 05:53 PM
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Central Michigan
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Slightly off topic, but related: Early 1990's Ford pickups with dual tanks and fuel injection used pressure from the electric fuel pump to push a valve to direct the return fuel to the correct tank. Of course the valve would seize up (there was a recall to replace them). If a driver filled both tanks and selected the tank that would NOT get return fuel, they'd be driving down the road and pumping gas out the filler neck of the other tank. As a service writer, the first time a customer came in and said his truck was making gasoline was QUITE strange...

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