Near Disaster

[andygere]

After a 104 mile round trip tour with my son in my buggy, we stopped at a neighborhood gas station to fill the tank so I could calculate my fuel economy. The station is less than a mile from my house, and we went directly home, parking the buggy in the garage as usual. About an hour later, my family and I smelled gasoline in the house, and I ran downstairs to find the buggy sitting in a large puddle of gasoline. I quickly rolled it outside, and absorbed the fuel covering a 70-80 square foot area of the floor with kitty litter. My furnace and water heater are both in the garage, and I shudder to think what might have happened if I didn't go down and quickly discover the problem.

After I got the mess cleaned up, I went looking for the source. I couldn't find any leaks in any of the soft or hard lines, and it was bone dry inside the tunnel. The area under the fuel tank was dry as well, and the fuel filter feeding the carb was intact and full of fuel. The vent hose, which exits under the driver's side front fender, was wet with gas. The fuel gage shows that tank to be nearly full, and a dip of the tank indicates that's the case.

Could simple thermal expansion of the gasoline have caused it to come out the vent? It was about 50 degrees or less for our 52 mile ride home, and I imagine the fuel in the underground tank at the filling station was at least that cold. My garage was about 70 degrees in side, perhaps warmed a bit more from the heat of the buggy engine. I closed the overhead door almost immediately after pulling in.

Gasoline expands by 0.000950 gallons/ºF therefore:

∆V=(9.2 gallons)(0.000950)(20º)=0.18 gallons, or about 25 ounces.

It sure looked like a lot more gas than that, but I guess two full beer cans of gas on the floor could spread out pretty quickly.

The buggy sits on a 1972 pan, so it's a good guess that it's a 72 or 72 style tank, but I'm not certain of that. I've never seen the tank with the hood off, so I don't know exactly what the vent looks like. Any thoughts or ideas on this would be greatly appreciated. I definitely don't want it to happen again.

[LeeVW]

Yes, thermal expansion is your most likely suspect. My buggy has done this since the very beginning, back in 2002 when I first filled the tank. I now have to plan my trips to where I fill the tank, then begin driving immediately. If I let it sit too long, even in the shade, fuel will POUR out of the vent line.

The vent line makes three loops, but this doesn't help. The angle of the tank ensures there's a large pocket of air behind the filler neck. The vent line is in the filler neck, which is lower than the pocket of air, so the gas pours out.

I have chocked it up as just another annoying thing about my buggy.

Lee

[woodoctr]

I've seen this on at least 1/2 dozen kit cars over the years with various tank configurations. Only did it once on my current car. I just make sure that I only fill to the first click off on the pump and I've never had it happen again. That must allow enough "room" for that expansion.

[Dale M.]

Yes it was probably thermal expansion.... Got to remember what temperature gas is in tank underground (earth constant is about 55°f)...... So when ambient (air) temperatures warmer, it will warm fuel and it will expand....

Used to be when "racers" were doing coast to coast runs (Gum Ball Ralley) they would always fuel at night to get more volume (condensed fuel) when it was cool...

Dale
_________________
“Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.

"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

[Q-Dog]

Thermal expansion sounds plausible, but, fuel will only get pushed out of the tank if the vent is submerged in the gasoline in the tank. The vent line opening in the tank should not be below the level of the fuel in the tank.
_________________
Brian

'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle

[joescoolcustoms]

I always plug the vent and use a vented cap. If the vent is low enough off of the tank, even though it is routed higher then drops low, with a little pressue, it will start to flow, then continue to siphon.
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[VOLKSWAGNUT]

I've had this happen on a both my lowered Beetles and my Buggy,
Fill em up, park in the hot sun...fuel expands up the neck and out the vent tube.
Learned not to fill them up to the bottom of the neck if I was to park them soon after.

Good catch before the big bang.

.

..
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[andygere]

Thanks for the info guys. My vent hose hangs down a few inches below the fender, and I think some siphoning occurred as a result once the thermal expansion got things going. Both times I fueled it yesterday I filled only until the auto shutoff clicked, which was visually just to the bottom of the filler neck. I'm not certain if the vent hose is connected at the neck or somewhere else on the tank, as I didn't install it and have not had the hood off yet. For all I know I might have been dripping gas out the vent while we roared down Highway 1 at the start of the trip. I'm going to see what I ca. Do in the short term to raise the vent hose above the top of the tank so it won't siphon again. For sure I won't be filling up on the way home anymore, what a mess and a really dangerous situation.

Has anyone used the little motorcycle fuel vent check valves to solve this problem? I assume you just attach it to the end of the vent tube and it lets air in but closes if gasoline tries to bubble out. Can those lead to over pressurization of the fuel system if say you fill the tank on a hot day?

[andygere]

Here's an image of one of those little valves installed on a motorcycle tank.

Do these need to be installed in this orientation to work? It's not clear if it's a spring check or just a simple float.

[joescoolcustoms]

Try to find a vented cap, then plug the vent.

If you put a check valve on the vent, and it is set up to only let air in, it can over-pressure and end up pushing fuel through the fuel pump, over flow the float valves and dump raw fuel down the intake and into your oil. You will not know until the engine locks up.
_________________
Bad News Racing 2018 NORRA 1000 3rd in Class
Best Day Ever Racing 2022 NORRA 1000 2nd in Class and first All Female team to complete the race

Everyone is gifted. Some just do not open the package.

Looks like it was painted with a live chicken,polished with a brick and buffed with a pine cone

[andygere]

Joe, that's what I was worried about. I have a fuel pressure regulator, and my carb has a brand new float and float valve and the motor runs like a Swiss watch. I don't want to screw that up, and I don't know if the regulator would be sufficient to prevent the fuel charging the you describe. I had that problem before I ditched the electric fuel pump and don't want to relive that. Changing to a vented cap will take some doing, but in the long run may be the best solution.

In the water industry, we use something called a combination air-vacuum release valve. It allows air to vent out of the mains as they are being filled or operated, but lets air in as they are drained to prevent collapse. Water is not released in either operation. Is there a device like this for automotive fuel systems?

[joescoolcustoms]

Do you know for sure your current cap is not vented?

I have not seen what you describe, but that does not mean it does not exist.
_________________
Bad News Racing 2018 NORRA 1000 3rd in Class
Best Day Ever Racing 2022 NORRA 1000 2nd in Class and first All Female team to complete the race

Everyone is gifted. Some just do not open the package.

Looks like it was painted with a live chicken,polished with a brick and buffed with a pine cone

[andygere]

My cap is definitely not vented. It's a marine deck fill style cap, designed to keep water out and sealed with an O-ring. It looks like this:

[nightmanx11]

I have used the motorcycle vent on the last buggy I built. It took care of the problem with liquid fuel releasing thru the vent, but there was always a trace of gas fumes in the room. I think it allowed the gas vapor to leak out. That buggy lives in a trailer instead of inside the garage.

Joe

[Dale M.]

Drill 1/32 hole above "O" ring at down angle to intersect with under side of cap...

Dale
_________________
“Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.

"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

[andygere]

I did a little more investigating in the daylight today, and here's what I found.

The bottom of the vent hose hung down to about the level of the bottom of the tank. This certainly helped siphon some fuel out once the thermal expansion got it primed.

The vent itself is plumbed to the driver side of the tank, and there is a loop of hose that goes up to the underside of the hood. I couldn't see this directly, but was able to stick my phone underneath and get a decent photo. You can just see where the hose connects to a fitting on the tank near the center of the picture. The part of the hose in the foreground simply goes through a hole drilled in the fiberglass, and exits under the driver side wheel well.

There is no vent hose connected to the filler neck. You can see in the foreground where the original filler opening and vapor return line were welded up. I used my camera phone again to see what I could not.

Here is my temporary partial fix. I extended the vent hose and used a cushion clamp to route it as high as possible. Tension on the hose holds it under the driver side fender, which by eye is pretty close to the same height as the top of the tank. It won't stop fuel from burping out from thermal expansion, but at least it won't siphon. I'm guessing that most of
what landed on my garage floor was siphoned not simply displaced.

Note: My wife teases me about keeping little bits of hose like this and other seemingly useless parts, but I'm glad it was in my kit. I made the fix with materials on hand.

In terms of drilling a vent hole in the gas cap, what will keep fuel from bubbling out of that and onto may hood instead?

[joescoolcustoms]

You have a late Beetle fuel tank with a side vent.

No matter how high you route the hose, if the fuel level is above this vent in the tank, and heat differential causes the fuel to expand, it will push fuel out this hose. Having the end of the hose above the level of the tank will stop the siphon.

I only run vented caps and no other vent, and do not get fuel splash out the cap unless I park on a incline so steep it forces the air out slowly and then the fuel level is above the cap.
_________________
Bad News Racing 2018 NORRA 1000 3rd in Class
Best Day Ever Racing 2022 NORRA 1000 2nd in Class and first All Female team to complete the race

Everyone is gifted. Some just do not open the package.

Looks like it was painted with a live chicken,polished with a brick and buffed with a pine cone