The Stovebolt Site Forums The Shop Area The HiPo Shop Fuel tank vent hose is leaking gasoline and vapours

Hi, guys:

My rear-mounted fuel tank has a vent hose attached to a nipple on the top driver's-side corner of the tank. The rubber hose is about 2 feet long and is looped three times into a coil and zip-tied to the frame to keep it away from the exhaust.

I don't fill the tank more than 3/4 and it is still pressurizing while parked in the garage and it also vents both air (the garage always smells of gas) and also gasoline liquid.

A friend suggested adding an in-line rollover check valve to prevent the liquid gas from coming out. It would just be added to the vent hose.

Does that sound reasonable? Is there anything I can do about the smell of the vapours?

Thanks for your input.

John

Yes, sounds reasonable if you put the roll over valve on the tank, then add your vent hose.

The roll over valve will prevent gas from sloshing into the vent hose. Once it does get into the tube the tank can build pressure until it pushes the gas out of the vent line.

The vent valve will need to be mounted vertically to work properly.

As for the gas vapors.. if the tank is a vented system you will smell gas fumes unless you add a charcoal filter or some other such device on the vent tube.

Thanks John for the great advice.

By the way, I love your 65 C 10, especially the paint patina and your Camaro ice cube trays. A unique look. Way to go.

Here's a link to my' 53 rest on my:

https://www.dropbox.com/sh/nt9f4a9pyq6jn8g/AAD6RCdLPvfnHv5SeEiyovAwa

Cheers, John

Holy Frejoles.... your truck is gorgeous. Is that black a mile deep or just 3/4 of a mile.

Thanks for the kind words, John. Actually the black is 1.6 kilometres deep. I'm a Canadian, eh? lol

do you have a vent hose running to the fuel filler neck? or is that the vent hose that is leakin?
vent to filler neck

It's the vent hose that's leaking. It's about a 2-foot section of rubber tubing and has been coiled into 3 loops that sit higher than the tank.

I'll be in to town tomorrow and will stop by an auto parts place to see about the roll-over check valves.

All the best,

John

Get a rollover valve and shorten that hose. Having it coiled up defeats the purpose.

Thanks, Colin. I thought it was coiled that way on purpose to kind of stem the flow of any gasoline… Kind of like adding well casing higher and higher to stop the flow from an artesian water well.

I will add the check valve and shorten the hose. Cheers.

Love the look of your '46, by the way. Awesome patina…

A little gas smell is semi normal on a carb engine in a garage. Liquid gas coming out is not. That would be a vented system problem. Wrong/bad gas cap or plugged vent. A roll over valve will probably not change anything. (I believe they operate by gravity not pressure) After you eliminate the pressure in tank, it will not leak liquid and the smell will be almost gone. Some systems need relief from pressure and vacuum, some just vacuum relief. Some caps allow suction when gas level goes down and pressure relief for filling tank and expansion. You may have mixed up system types with whatever you have as a tank/fuel delivery/carb or injection, in-tank pump or engine mounted pump, etc. As said, no coiling of hose/kinking/mounted too low/ID too small. Try leaving gas cap loose to see if it fixes problem.

I should have clarified, I think what they did is exactly what you say. Instead of putting a valve in they just put a length of hose to put some backpressure against fluid flowing out. You're best off to have a check valve and a small length of hose going no lower than the top of the rollover valve.

Bartamos is right though, you could have another issue that's making it pressure up. Is it only doing it while sitting, or does the tank hold pressure after you go for a drive?

It seems unusual that fluid would come out of the rollover valve if you don't fill the tank above 3/4. Are you sure it's the rollover valve fitting? As Bartamos was saying, some tanks are set up for EFI. I'm wondering if the hole you're feeding into actually has a pickup tube in the fuel in the tank?

I've had the same issue happen before but not with the vehicle sitting and it has to build a considerable amount of pressure to flow out of the vent if the vent tube isn't in the fuel. It looks like a car tank of some sort with the rear fill? It might have had a vented cap at one point.


Thanks for the comments, I love it too! Your truck looks great, I love the interior, you did a great job!

In Johns original post he states the vent hose is coiled 3 times. I am betting that was done to keep water and other road debris from getting into the tank via the vent line. Good intent, but with bad results.

When he drives the truck the fuel sloshes around in the gas tank and some of the liquid gas ends up in the vent line. The liquid gas becomes trapped in the 3 coils (that's the problem). The liquid gas in the vent line now creates a liquid seal and thus the vent line no longer performs its required function of venting gas fumes at atmospheric pressure. (Same principal as a P-trap on your kitchen sink and toilet, the liquid seal is why you don't smell sewer gas).

With a non-vented cap on the gas tank, if the fuel in the gas tank warms up the tank will build pressure due to the trapped liquid gas in the vent line coils. That pressure pushes the liquid gas in the coiled vent line out and thus it pukes the trapped vent line liquid gas out after it has been parked, again because of the coiled vent hose. (Kind of like flushing a cherry bomb down a toilet results in the water in the line to puke out of the toilet and sinks.)

The roll over valve will fix the gas puking problem. It won't however stop the smell of gasoline vapors, if the vent line is working it properly it will vent some gas fumes when the liquid gas warms up and expands. Newer cars have charcoal canisters on the vent line of the gas tanks that scrubs the vapors and prevent the gas smell.

Wow, thanks for all of the great input, guys. As they say in Latin America, es muy complicado.
I'll let you know how it all works out when I try the shorter hose and the rollover valve.
Much appreciated.
(By the way, my gas cap is a non-vented marine one, if that makes any difference…)

I installed a under bed tank on a 66 C10 and mounted a charcoal canister to the rear as far above the tank as was possible.
I picked one up at the wrecking yard but I think they are available new.
It worked fine but still had to leave a couple of inches below the top of the tank for expansion. It should eliminate the fuel smell in the garage.
Fred

Mission accomplished! I delayed reporting until using up two tanks of fuel to be sure the fix was permanent.
As recommended, I straightened out the hose and eliminated the coils. I also added another couple of feet and routed it up high over the tank and then even higher.
I drilled up from underneath the back left corner of the box and routed the hose up through the hollow corner support of the bed sidewall. I secured it just under the flared top flange of the bed, just below where the tonneau cover makes contact. There is a small drilled hole in the side of that corner support and any vapours seem to vent out there OK without filling the covered rear bed with the smell of gasoline.
I decided against routing the hose up into the wheel well, fearing that dirt and water could find their way back into the fuel tank.
The burping fuel problem has been eliminated and although there's a slight smell of gas at times in the garage, I guess it's to be expected with a carburetor and my dual exhaust when backing in.
Thanks again for the great advice!

Thanks for the update!