I'm trying to get some advice as to how to properly vent my gas tank on my '53. It is a rear mounted baffled stainless tank that has the filler mounted in the bed of my truck. The gas cap is non-vented, it is the smooth cap/filler from mid-fifty. I have it vented from the filler neck, but I'm not too impressed with the setup. Anybody have any advice?

 

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I put a couple of loops in the vent hose and terminate it as high I can. I always point the end of the hose towards the front of the truck to help keep the gas in the tank on hard take offs. A one way valve would eliminate all that, but not sure where to get one.

 

per "no limit" my tank has an in-line fuel filter in the vent line to keep out dirt and moisture. It comes off a fitting on top front corner of tank.

 

While on the subject of gas tanks, I,ve got a Hagan fuel door mounted in fender. It has the type of cap that you don't remove, you just push the nozzle through the center of the cap.

I,m not real happy with this set-up because the pump keeps kicking off when I'm trying to fill it.

Does anyone have any suggestions?

 

You and I think alike. That is the current setup that I have and I am also looking for a one way valve too

 

Sounds to me that your filler hose is too small or has a sharp bend in it.....fuel isn't flowing into the tank as fast as it is being pumped. I'm having to rework my whole filling setup as I am having this exact problem as well....and since I am wanting to rework it I thought I might see if I could vent it a little differently as well. But, it doesn't seem that there are too many options

 

A pcv valve is a simple one way valve that can be found in a number of sizes and configurations some of which fit rubber hoses. are you trying to vent it for filling or for pulling air in as the tank empties?

 

I need it vented for when it empties...while the engine is running. That PCV is a good idea, I hadn't thought about that

 

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If this is happening and your vent is in the filler neck, wouldn't there be air trapped in the tank? Could this be your problem when filling the tank? The poly tank in my truck has the vent coming out of the sending unit, and it fills fine. Does that make sense? That would give the air somewhere to go when the neck is completely full of gas.

 

New vehicles use a charcoal cannister with a purge valve and use a non vented cap. These caps are marked Pressure/Vacuum and have a release valve at 15" of vacuum and about 4 psi. This release valve built into the cap is to protect the tank, which when made from light sheet metal or plastic, can distort and bend the tank walls. These tanks would be considered non vented. The cannister, with a purge valve which is hooked to the vacuum system at the intake manifold handles the venting. This type of system isn't that bad as it doesn't require a vent. When filling a tank with a smog system, the bellows on the nozzle handles the venting. The hoses on these type of gas pumps are two chambers, one for venting, the other for gas. They also fill slower than an open nozzle.

Vented tanks, (no longer allowed on new vehicles) to avoid fuel spillage when the tank is filled to the top, have to run the vent line to a higher place than the tank. If the filler is high enough at the cap (4-5" minimum over the top of the tank), and the tank is baffled, this should suffice. Frame mounted tanks on big trucks, just use a tight fitting screw on cap with a pressure vent. For a pickup, it is really easy to run a line from the tank forward to the front of the pickup bed between the cab and the bed in a loop with the end coming from the loop going down to a spot that can dump gas directly on the ground without running on an exhaust pipe or something. This allows constant venting of the tank which avoids any pressure or vacuum buildup from temperature changes. This is also important when running a carburetor, that pressure does not build up in the tank.

The other problem mentioned, that the pump shuts off when filling probably means when filling with a smog pump. An open vent will help, as will a larger fill pipe. "Slipping" the bellows up above the tank filler will also work. However, the quantity of air displaced by the fuel pouring into the tank is far more than a 5/16 vent line can handle. So the vent makes very little difference with the shutoff on the smog pump. Some vehicles with very low fillers like early Ford Falcons/Mustangs, had the gas tank as the trunk floor with a short 90 degree filler. It is almost impossible to fill these with smog pumps without a very long fill time and they leak on the paint while fillling. One fix for this is to put a straight filler on the tank and open the trunk to fill it. The straight filler reduces the gas vortex created due to the 90 degree bend which interferes with venting the air. The very short nozzle used with a smog pump causes the vortex whilch would not occur with a longer filler nozzle. When using a frame mounted gas tank with a pickup bed, the best solution is with a relatively straight filler pipe. I would prefer a filler pipe hidden in the rear fender area rather than in the pickup bed. The pickup bed is the last place I would want fuel spillage. With my flatbed truck, I removed the cab mounted fuel tank, and used two 20 gallon round tanks mounted on the frame. They each have 4" high filler pipes with screw-on caps which have a pressure vent in the cap, and the vent hoses on the tanks go to the frame of the flatbed behind the cab. This makes the vent hoses about 14" above the tank, and about a 3' run. They have never leaked fuel, and I never fill the tanks completely, leaving about an 1"-2" of air space. This allows the fuel to expand on a hot day. The gas you buy is cool, having been stored in underground tanks, and it can really expand on a plus 90 degree day.

 

Old post and it did not quite answer my question.
My off topic vehicles (33 chevy,54 ford) sit in my enclosed garage for periods of time and my garage has the aroma of gas in it. I am thinking this is from the vent line off the tank. I have heard that you should run the vent line 4-5 inches higher than tank and thru a charcoal filled canister to help eliminate the smell. Any more ideas on this. Somewhere I have seen these cannisters but can't seem to find them now.

 

nevermind.

 

sorry double post

 

Charcoal canister on the vent line will help, but then there is the issue of purging the tank. I run canisters on my fuel injection retrofitted cars but the PCM controls the purging of the canister and I run fully sealed systems. I have one I am doing now that the PCM does not match the EVAP hardware and am going to have to purge it another way, possibly off a temperature controlled vacuum switch. I guess you could run the purge line to the air, but then once the tank pressure got high enough the vapors would just burp out to the garage anyway.
You can grab a canister off just about anything in the boneyard, I have a supply of 93-95 Z28 and caprice canisters so I use those.

I see this thread was from 2006 but the info is stil relevant.