2nd Gen Non-Engine/Transmission Fuel tank pressure or vacuum

[Paul Somers]

Just returned from a trip and noticed at every fuel stop there was either a pressure or vacuum in fuel tank. Couldn't tell if it was blowing or sucking when removing fuel cap. Have owned this truck since new and never noticed this before. Has anyone else noticed this and is this normal and I've just never noticed?

 

[GKinney]

tank

You are hearing vacuum releasing when you take off your cap. No it is not normal, you have a plugged/clogged roll over valve on top of your tank. Mine was the same way, I just took an air hose and blew back into the plastic nipple on the valve, didn't take much to clear it. If you leave it that way, you run chances of not only starving your lift pump for fuel supply, I have heard it can even suck in the side of the fuel tank, hard to believe since it is a 1/4" thick!! Hope this helps you out. P. S. always nice to see fellow hams on here!!!!

 

[GW01]

i have a 99 3500 with the same problem. i posted the problem here several months ago. its possible that the factory left a cap on the vent valve . do a serch on vacum and you will find info on the vent. i think i will follow g. kennys advice and use air in hopes that it is clogged

 

[GKinney]

forgot

Yes gw you are right. I forgot that there was some of them that the rubber cap was left on the vent. Easy to check though,, if it doesn't have the cap on, probably the thing is full of dirt. I found taking my wheel/tire off makes it easier to get under the fender to blow it out. Sure beats dropping the tank like I did last Fall!!! Good luck.

 

[ralbert]

Hello, I read this post while camping in Fla this winter. I have had this problem for some time and I have been running with a loose fill cap so vacum would not build up and also would keep my lift pump from going south. i have had three of them. My question is can I apply a low air pressure charge to the tank thru the filller neck ? I would think that would unset the ball or stopper in the valve. I have a pit in my garage so I can get under it very easy but someone stated to go thru the left rear wheelwelll. Maybe that would be easier. Thanks Rob