The Stovebolt Site Forums The Shop Area General Truck Talk Gas tank overflowing

I've had my '53 3100 for over two years & have never had this problem. I filled the tank a couple of days ago. Tonight I noticed gas leaking from the fuel cap. I removed the cap and the tank "burped" and the fuel receded. I left the cap off, checked it later and the fuel level was back at the level of the cap. I started it up & the fuel level dropped again. What's going on?

I've had mine expand and overflow if it was filled all the way to the top and it was a really warm day. Most of the time I don't put that much in it so it's not a problem. I'd suggest not filling it quite so full next time.

It sounds like expansion due to warm temps and over filling. I suggest next fillup, when the nozzle shuts off the first time, don't add more. Or fill until the guage reads full or just under and stop.

I've done the same. If you're going to fill it up to the tip top you need to drive 5-15 miles before parking for the day. Also or try to park with the filler on high side if possible.

An additional thought. If your tank "burped" when you removed the cap, the cap vent may be plugged.

Depending on the cap.
Most new caps allow air to enter but build a little pressure if the fuel expands, they're not freely vented like the old/original caps were.

Grigg makes a good point.
Many of the off the shelf "vented" caps comply with the EPA standards to reduce gasoline vapor. They have a one way valve that lets air in as the gas level goes down but don't let anything out. I've seen huge pressure buildups in some tanks.
I remove the spring from the valve if I can't find an old style cap.
And yes, don't fill the tank above the bottom of the filler neck unless you are going to burn off a couple gallons before stopping.

I listen to the filler neck when I'm filling. As soon as I hear a unique gurgling sound that I've gotten use to which to me is when the tank get's close to full, but before the gas starts hiking up the filler neck. That's when I stop.

Interesting. I wasn't aware that the new caps had a one way vent. I guess today wasn't a total waste.

Thanks for the comments, everyone. I think it's the gas cap as the weather here in Ohio was in the 50's all day so it probably wasn't due to heat expansion. It burped again when I opened the cap so I'll look into that issue.

That sounds like an annoying issue. I never fill my truck more than about 3/4 of a tank because of similar issues. Luckily for me she is a toy and not a daily driver. That being said, if I am going to go cruising I can fill her up all the way because I know that she will burn off the top part of the tank anyhow.

Kyle

The new cap I recently purchased had a one-way plastic valve in it, and I drilled a 1/4" hole through the plastic. No more rediculous tank pressure.
This excess pressure can't be good on the float needle/seat in the carburetor.