# Gas Tank Vacuum



## schatman (Jun 29, 2007)

Hey,

I've noticed that I've been building up a large vacuum in my gas tank while I'm driving. There's a huge intake of air when I remove my gas cap for filling. From the diagrams of my gas tank (from courtesy parts) show a ventilation valve from the tank ending near the gas cap, and a second ventilation tube with a valve. What's the chances that its the valve that doesn't work anymore? Anyone know how often these valves fail? And is driving with a slightly cracked gas cap okay until I get a new valve?

Thanks,
Shawn


----------



## schatman (Jun 29, 2007)

Or could it be the gas cap?


----------



## greenbean699 (Jan 18, 2004)

i would first change the gas cap. then look into it more if need be.


----------



## sunnysentra (Jul 24, 2002)

172 Fuel Tank :: Fuel & Engine Control :: Genuine Nissan Parts :: Sentra / NX (B13) 1991-1994 :: CourtesyParts.com

Look at the parts site here. There are check valves and breathers. I just bought the 17370 check valve. then the breather. I did this when I replaced the Fuel filler, hoses and such. I thought that after this many years, these could need replaced. 

The gust of vapors when you pull the cap may be just having the tank warm in the sun or something like that. But, those valves should release that pressure. 

Chris 92 classic


----------



## Dan9 (Sep 18, 2004)

I have the same problem, it never goes away. I have changed out not only the charcoal canister in the engine bay, the solenoid switch for the EVAP system, and the little canister under the tank, but I have changed the gas cap 3 TIMES. When I did the charcoal canister the old one was clogged with fuel??! The first new one I bought was defective, I returned it to Nissan and they tested it and gave me my money back. Then I was using some old cap, now another new one, same darn problem.

I do not understand how after 30 seconds of running a vacuum can be building up inside the gas tank, unless something is not letting air get sucked INTO the tank. I know a little vac is normal, but this is a LOT.

The only solution I found is to crack the gas cap. But that lets stinky vapors out that somehow get sucked in the drivers open window and that sucks.


----------



## schatman (Jun 29, 2007)

That's what I've been doing lately as well, to let air in! I've heard of fuel pumps working overhard to fight the vacuum. So I've tried another non-new gas cap, but it still holds vacuum.


----------

