I did a bit of research and couldn't find the answer so I'm hoping the experts on this site have either experienced this before or could lend some helpful advice.

We had a pretty hot day here, around 92 degrees..after it's been around the mid 70's for about a week or so. I filled my gas tank on Saturday, and drove around for a bit...so far so good. I go out in my garage tonight and smell gas, so I look under my car and there is a puddle of gas under the gas tank ...earlier when I got home from work there was not even a slight gas smell.

I checked the tank thoroughly, no leaks on the tank itself or in any of the fuel lines. I removed the filler cap and saw that the gas was actually backing up out of the fill nozzle and dripping out onto the floor. I was able to stick a rag in there and soak up a lot of the excess fuel that had collected in the fill nozzle but have a feeling this will keep happening (we have a few more consecutive days of hot weather coming).

What could be the cause of this? Should I be overly concerned? I know with heat comes pressure, and could just be causing the fuel to back up, but isn't there supposed to be a safety in the fill nozzle to prevent this from happening? Added note, we have had quite a few REALLY hot days this summer and I've never had this problem, so I am very confused as to the cause.

Sorry for the long story, but I'm pretty nervous to even start the car to get the fuel level down some more. Any help is greatly appreciated.

Jeff

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition

There's an air space above the gas in the tank.

The bottom of the air space is where the bottom of the fill tube is.

Once gas hits this level, it goes up the tube.


I suppose it's possible that you filled the tank up when it was cold, and heat caused the gasoline to expand until it had nowhere to go but up the tube.

Usually this doesn't happen because there's not much of a temperature difference for gas expansion, and driving around lowers the gas level making it impossible

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Thanks for the reply, I figured it was something odd that shouldn't really have happened, especially at night when the temp cooled down a bit.

I'll have to check it again today when I get home and hopefully it'll have gone down a bit. May also be the gas cap has a weak seal on it and can't hold the gas back from over-flowing.

Like I said, it's odd that we had weeks of hot weather around here and this never happened....maybe my gas tank just wasn't as full as it is now.

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition

Gasoline expands quit a bit when heated. Remember the ground temperature in NY this time of the year, where the storage tanks are buried, is probably around 50 degrees, bump the cold gas up to 90+ degrees, and it will fill the fill tube quiet easily.

When it is hot in the North East during the summer, it is a good idea not to fill 100%, if the car is going to be parked within a mile or two of that fill up. If you are going to drive 20 miles after a fill up, the level will be lowered by a gallon or more, so there is room for expansion.

A few more days and this won’t be a problem for another ten months around here. LOL

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

haha, too true...and sad at the same time, not looking forward to winter at all. I got home yesterday and noticed an even bigger puddle under my car so I took the initiative to siphon gas all the way out of the fill tube, drove it around for about 30-40 minutes and pulled into my garage forward...I typically back in, but my garage has a slight slant to the back. Even after siphoning the gas out the gauge still read FULL...so it's possible the shutoff on my tank isn't working properly and allowed me to over fill the tank in the first place.

I know that gas expands when it's heated but isn't there supposed to be a vent somewhere to prevent it from over-flowing? Without venting, I see it causing a "p-trap" effect where the volume is moved by increased pressure.

Hoping this worked but we shall see when I get home.

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition

My van does the same when it's hot. I don't have a vent tube on mine as it didn't come the factory with one. Check your vent line for obstructions. I can't fill mine over 1/2 full in hot weather, and the way I park the back is higher than the front. It's kind of a PITA to only keep it half full, but ya gotta do what ya gotta do to prevent it. I have a vented cap and it says on the cap to watch for pressure when opening, go fig there?

Yeah make sure it's venting correctly. Im in Sacramento and it gets 100*+ during the day and down to 65* at night and I've never had a leaking problem like that.

After siphoning out some gas and pulling my car into the garage forward I haven't had a leak, it's been 95 degrees the past 2 days and so far so good...I'll just have to remember not to fill it up all the way. The stop on my tank may not be functioning properly either, allowing me to over-fill the tank a tad.

I will double check the venting when it cools down and go from there. I appreciate all the help guys

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1963 Plymouth Fury 4-door, 225 /6, 3-speed manual w/ OD, "super six", Mopar electronic ignition