The Stovebolt Site Forums The Shop Area General Truck Talk Gas Tank Venting

I hope this is in the correct forum ; sort of interiors, sort of engine… I don’t know.

I am noticing fuel vapor smell in my cab after the truck is parked for a spell.
‘54 3100 , modified, 283 w/4bbl , replacement fuel tank in original location behind the seat. I’ve checked closely at the top connections all seems clean.

I’m wondering about venting. My gas cap had a paper-like gasket; the cap to fill neck connection was loose and wobbly. I replaced that flimsy washer with a substantial rubber one , now the cap is quite snug when it is seated. I recently filled the tank and the vapor seems worse. I’m wondering if the close fitting washer is preventing ventilation of the fuel tank.? Or do I need a different cap?

Id put the paper like one back on and check vapor if it goes back the way it was.

what type of gasket are you using at top of the tank for sender.
I noticed if I overfilled the tank or filled it then parked it in the sun and the gas expanded enough to fill the tank. The gasket would weep just enough to smell. One drop of gas goes a very long way for smell.

I noticed my vented gas cap to a lot of pressure to vent. Most likely your paper was venting more than the one with the better seal.

I solved my problems by splicing a T in the vent line behind the seat. Put a loop behind inside metal up and back down so it was above the gas cap then put a vapor canister under the truck bed.
No issues with pressure or venting smell of any kind since it all goes thru the vent.

also it looks like your gas cap may not be vented. put it on a tube that cover the rubber and blow in and suck out and see if it goes both ways
If its not vented then the paper was releasing the pressure enough but the rubber is not.

Most vented ones have a hole in the center to vent. I don't see that with yours.

If its not vented then the pressure is building up enough in the tank to find just a spot to get out inside the cap.
Normally windows up and it venting by the cap you should not have a smell inside the cab

My sending unit has a thin rubber gasket that I supplemented with a gasket seal product. I wiped the surfaces around that unit with a clean paper towel today and it came up clean.
I suppose it’s possible that vapor is passing that seal while liquid fuel is not. Perhaps the snug fit of the rubber washer is sealing well enough that venting is occurring elsewhere? There are a number of connections.

My gas cap is probably not stock. I might just drill a small vent hole in it. What do I have to lose?

If you manage to seal the tank well enough to prevent any vapor from escaping, a good fuel pump will collapse the tank, or the engine will stall from fuel starvation. There must be some way for air to enter the tank as the fuel is consumed. I'd suggest fabricating a proper vent system that lets the gas vapors escape to the outside of the cab.
Jerry

What do you think of the mid-70s evap systems that vent the tank into a charcoal canister with a hookup to the carb to draw the vapor back off and burn it?

My truck has a vented gas cap like the one in the photo Guitplayer posted above. I also have a new sending unit gasket on the new tank. No fuel smell in cab. Definitely get a new gas cap. Cheap from Rock Auto or wherever

Are you sure the fuel smell isn't coming from under the hood through the firewall or whatever?

Modern gasoline evaporates at low temps and makes your carburetted car smell like gas whenever it's parked.

Just offering a different perspective. Have you checked the hoses and hose clamps used to connect the external filler/vent pipes to the fuel tank filler neck and vent tube???

Those hoses do occasionally go bad and the hose clamps can loosen up allowing fumes to enter the cab. Just worth investigating IMHO.

A U-shaped tube teed into the filler neck that rises above the level of the fill cap and then finds its way to the outside of the vehicle would be the simplest way to achieve a good vent. The charcoal canister and purge system is just lipstick on a pig- - - -something the tree huggers insisted on in the 1970's that had no real purpose other than self righteous virtue signaling.
Jerry

When I stick my head under the hood there is no significant gas smell- but then the engine compartment is very well ventilated.
I left the gas cap off for the night. Tomorrow I’ll see if that deliberate venting made any difference. All of the filler neck and vent tube connections look clean and new (they are actually new) , and all were dry today. There is no drip evidence under the truck.

I’ll report back after tomorrow’s inspection.

Today I think I sense a decrease in fumes , possibly associated with a reduction from full to 3/4 tank, but the difference is not profound. Could be wishful thinking.
I left the gas cap off overnight and drilled a vent hole in my generic cap this morning, so there is no problem with venting pressure.

I am pretty much stumped. I guess I could pull the seats and gas tank this winter, inspect the bottom of the shiny new tank… not a job I relish.

Oh, the tank is brand new? You just put it in?
Could be a seam

Tank is about 3-4 years old, but the truck has only been active since October of last year.
The gas vapor issue has developed gradually over the last month or so. Seemed to increase with full tank about a week ago. Tank now 3/4.

Yes, it sounds like a leak developed somewhere. What about the fuel filler neck attaching points?

I carefully ran my fingers over all those connections today , in good light. Hands came up clean and odor free.

One of the ways I find some "random", "small", "a drip ever once in a while" leaks of all kinds is the paper towel method.
lay some clean white paper towels flat under the tank especially around seams.
wrap / tape them around the sender and joints. make sure its flat on the seam/seal of the sender.
Same with filler neck.
Let them sit for a while and then check them in a few days. carefully slide out the ones under so you can line up the drip with the tank if its there.
If there is a drip it should stain the towel even if it evaporates.
Cardboard under the tank will work for this too.

This works best with a full tank to the top. so its pushing out liquid.

since you thought it may be a pressure issue originally with the change of paper/rubber seal of the cap.
I would start with the cap that may be holding pressure or not venting. Put truck in sun in let it build up pressure this will help make the leak happen. "SLOWLY" open the cap after some time.
You could clamp the hose going to pump under the truck. you can also manually put a SMALL amount of pressure in the tank with a air pump. I used a power steering / radiator vacuum rubber seal kit and pumped in.
Since the smell is inside the cab it should not be a cap issue unless the cap is not releasing pressure which this test will tell you.

Thank you for that detailed advice.
To clarify:
- I drilled a hole in my generic gas cap yesterday; venting at that point is no longer in question.

- The access to the bottom of the tank in a behind the seat installation is extremely limited.
I might be able to shove some absorbent material under the tank from the side; I’d have to be careful to avoid a situation in which I can’t retrieve it.

Old trucks are fun.
Right?

with the seat folded and forward you should have access. card board pieces long push in from under front of seat in sections. as well works for under.

My trucks need a 3/8 ID vent , tank to the filler neck.
But mine is an under bed.

A smart guy , who bears a vague resemblance to me , installed bucket seats. Non-tilting bucket seats , in fact.

my '63 sending unit gasket was bad and when I replaced it i used the aviation permatex on the gasket as well as on the screw threads. also the rubber connection on the filler tube needs to be looked at and clamps tightened. if you have dry rot, replace. vapor may not be wet,but sure can stink.

I reset my sending unit using Permatex a year ago.
I think I’ll back the screws out one at a time and dress the threads with that sealant.
It’s a bit of a shot in the dark, but given the fact that the issue seems to vary with fuel level it can’t hurt.

I got your non tilting reference. Yea imaging that is not making this easy

???

Edit/addendum:
Non- tilting bucket seats–-
Got it , and it only took me a couple of days.

I have resigned myself to the fact that I need to pull my gas tank this winter. (Fortunately my truck lives in a heated building in the off season.)
My fuel level is down to 1/4, truck sat still for 2 days, (no sloshing of fuel up to the sending unit connection) , still had gas smell this morning. I’ll inspect the lower seam , get it tested if necessary. Otherwise I’ll probably be chasing that annoying issue next season too.
I guess that will give me a good opportunity to add insulation to the back wall of the cab , the only area that is untreated.

It never really stops , does it?
I thought I was done dealing with gremlins when I parted company with my 55 year old 34 foot sailboat …

It never stops. Thats how I know I am living.
I cannot imagine whats going on. But I`ll tell you thats one of the
main reasons I moved my tank under bed. I had old trucks(ford) back in 80`s and they had
that same issue. Unless its obvious(seeing wet/gas) ,its a hard problem to correct.
Good Luck!

any rubber non steel hoses should be replaced since your pulling your tank. This will help eliminate any pinholes that could be causing it as well or just a bad seal hose to fitting/filler
all the best.

and my non tilting comment was about your seat you (or someone resembling you ) installed.

I get some little crumb of credit for finally figuring out your “tiling” reference- and I accomplished that before I read your last post.

Hoses are only 1 1/2 year old , but I will certainly go over all connections and details. This issue developed over the past few months, there is a source somewhere, it’s not a very complicated system.

Put truck together , take truck apart.
Put truck together …….

Ski, I see according to a recent reply post in your Cab Mount Access Interiors forum thread that it seems you found the probable source of your fuel odor in the cab to be from a deteriorated main fill hose. Glad you found the source.

You also mentioned that in wrestling out the fuel tank that you had a minor oops that knocked off the "fuel line fitting". Question on that subject - is the tank by chance a "Spectra" replacement and is it less than 3 years since purchase??? It may be that the tank could still be under warranty if that's the case.

See this related "Fuel Tank Outlet Repair" thread as it may relate to your tank issue too.

Interesting. I wonder if there was/is a problem with the attachment method?

Dan-
The tank was one of the few new equipment items in/with the ‘54 red neck hot rod when I bought the FrankenTruck in Iowa in the summer of ‘20. No idea if it’s origin.

Otto - I must say that I was a bit surprised at how little force it took for that fitting to dislodge from the tank. Makes me wonder how sound that solder bond was. I was lifting one end of the tank to try to get a look at the connection and I had a leak on my hands before I realized what was happening. Maybe best that it’s going to be re-set.

Which brings me to –-
I am wondering if there are options other than solder I should consider…. Weld? Drill/tap / Permatex?

I should probably get some pictures and start a new thread for that info.

Does your break look anything like this? Almost no force was applied to it when it broke. I initioally assumed it was weakened because I had no flex connection on the fuel line but I don't think that's true after seeing how it separated.

If Spectra doesn't send me a new tank for whatever reason, I intend to take the tank and flange to a radiator shop and let them repair it.

Otto, looking at your pics, it may have been a cold solder joint. I say that based on the bubbles at the interface where it broke loose. Waveski's issue may be the same. A good solder joint will have a real close fit between parts, which makes the joint stronger than a thicker layer of filler material, actually stronger than the filler material only. Machinists will know about how you can stick gauge blocks together without anything but a tiny amount of oil between them. The best joint will have the two pieces clean and flat to within a few thousandths of an inch and the solder wicked into the joint by capillary action.

Otto , mr Hansen,
I think my failed coupling does resemble the on pictured.
Cold soldering , eh?
I’ll get pictures tomorrow for comparison.

www.youtube.com/watch?v=gbZt_9URtnw

In the past half hour I have learned a great deal about cleaning and purging gas tanks.

The link displays a method I probably will not use.

That guy is lucky the tank didn't split at the seams and hit him in the head. It was a pretty heavy gauge tank. One pressed out of sheet metal would have probably exploded.

I wouldn't recommend doing that.

The procedure involved duct tape ; it has to be bonafide.

A definite "How Not To Be Safe" example! Judging from the condition of his hand when he lit the propane torch, it looks like this unsafe method has already bit him at least once. Looks like he didn't learn his lesson from the first time.

Please keep further conversation on the topic of fuel tank repairs to safe methods only. Stovebolt strives to foster safe work on our trucks so we can all be around to enjoy them. Lets not give anyone the idea that this type of unsafe act is condoned or supported in anyway please and thanks!