Hi guys.

My 69 Camaro builds up pressure in the gas tank after running or on hot days. I get a pretty good rush of fumes when I open the gas cap. I have a new tank with single 3/8" line and new GM sending unit. All new lines. No gas smell in the garage so the fuel system is tight. The car seems to be running fine. I have tried a couple of new GM "Vented" (stant) anti-surge gas caps just to see if it made a difference and it did not. My understanding is that vented caps prevent vacuum buildup in tank and fuel starvation but do not allow pressure release. Is the pressure buildup in the gas tank normal?

Thanks for your help.

 

I had the same problem on my 69 when I replaced the old cap with a shiny new "vented" one I bought from the parts store. Pressure built up so high that it was making gas leak out past the sending unit gasket. Because of standards to prevent fumes from venting into the air, the newer "vented" caps are designed to vent in and not out. So my old (truly vented) gas cap went back on, problem solved.

 

Thanks for the info. I didn't think it was normal. Is your vented gas cap an "anti-surge" also? I assume that's to keep liquid fuel in the tank on acceleration. Do you think I could order a "vented" cap for an older or other GM product and get the venting both ways? I might try that and see how it does.