About a month ago i replaced the rubber hose part of the fuel lines that comes off of the tank. When i did i noticed that the atmospheric vapor line that comes out of the tank and runs to the vapor canister the plastic nipple had broken off...

I ended up putting some RTV sealant over the nipple to seal it from allowing dust into the tank and plugging the emissions line running to the vapor canister. When i did this i didn't realize that it would cause a tank pressure/vacuum problem and when i went to put gas in the truck and tried to remove the gas cap a lot of pressure from the vapors had built up and i knew that wasn't good so instead of drilling small holes in the gas cap to relieve the pressure i cut a small piece out of the rubber gas cap seal to allow the vapors to release into the atmosphere...

I bought a locking/venting gas cap today from oreilly's

http://www.oreillyauto.com/site/c/detai ... &ppt=C0333

thinking this would relieve the pressure and help keep from losing gas from evaporation...but it seems like there is still a lot of pressure building up maybe not as much as it was before i cut the seal on the other cap but enuff for me to be concerned about the tank over pressurizing and creating a vacuum and causing the tank to collapse itself...

Autozone sells a venting gas cap

http://www.autozone.com/autozone/parts/ ... 3397_5269_

and it says "Specifically designed pressure and vacuum relief valves to prevent evaporation of fuel. A leaking fuel cap can allow up to 30 gallons of gasoline to evaporate over the period of a year."

I figure that the oreilly's venting gas cap does the same thing but there are not features & benefits description about the one i bought from them

I guess my question is will this type of venting gas cap be enuff to prevent my tank from collapsing because of over pressurizing because i now have no atmospheric vent from the tank?

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1984' Dodge D150 Utiline Bed
Slant 6 225, Holley 1920 Carb
A833 4 Speed O/D Transmission

Those both have the same picture for that product...and someone is just better at adding more words to one catalog entry than the other (look like they come from the same distributor of parts from a quick website search).

Either way you need to clear up the venting issue, cap or hose from the tank to the charcoal canister, with a good port. Two things will happen: 1) long duration diving will eventually create a vacuum in the tank which won't collapse it, but it will make it harder to pump fuel out of it unless relieved...2) if the gas is evaporating it will cause the tank to expand and pucker until something gives (seal, cap, tank seam, etc).


-D.Idiot

D.I.

I guess the venting gas cap isn't going to do what i need it to do...it seems like it's not going to vent the vapors enough to keep down the pressure build especially when driving. I guess they are not designed for that and more just to help keep from vapor leaks instead of maintaining a certain tank pressure.

How much pressure should the tank have on it? After cutting the seal on the old cap i'm sure it didn't have any pressure...but i feel like the tank should have some pressure to help maintain the fuel line pressure

The piece that is broken i'm sure is not available i would probably have to buy another tank. The tank has a (return to the tank line) i wonder if it really needs it and if it doesn't then maybe i could use it for the atmospheric vapor line to the canister?

I'm going to keep a check on it over the next couple of days and see how it does and how much pressure builds...

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1984' Dodge D150 Utiline Bed
Slant 6 225, Holley 1920 Carb
A833 4 Speed O/D Transmission

The tank doesn't need any pressure, the fuel pump does a great job of sucking up gas then pushing up the tube to the carb...If it has enough pressure, the fuel will overcome the pump mechanism and push the fuel into the carb after overcoming the needle and causing your engine to flood while parked.

If you aren't using the return line, I would plumb it to the canister or a fuel filter open to the air to catch the vapors (worst case scenario).


-D.Idiot