JPP Posted October 15, 2017 Report Share Posted October 15, 2017 I have recently got my truck going and so have had the pleasure of filling up at the gas station. I have noticed that when I open the cap, a vacuum is released, is this normal, or should I vent the cap? Thanks Quote Link to comment Share on other sites More sharing options...
John Rogers Posted October 15, 2017 Report Share Posted October 15, 2017 There should not be any vacuum or pressure built up in the tank. They are supposed to have vented gas caps. John Quote Link to comment Share on other sites More sharing options...
The Oil Soup Posted October 15, 2017 Report Share Posted October 15, 2017 The vented cap should only allow air flow into the tank and not out so it will build pressure inside and not let fumes out. Generally when you open the cap it is releasing that pressure. Quote Link to comment Share on other sites More sharing options...
TodFitch Posted October 15, 2017 Report Share Posted October 15, 2017 12 minutes ago, The Oil Soup said: The vented cap should only allow air flow into the tank and not out so it will build pressure inside and not let fumes out. Generally when you open the cap it is releasing that pressure. There is no one way or check valve in the vented gas cap on my old Plymouth. I'd be really surprised if there was a one way flow mechanism built into any car's gas cap until the advent of fairly strict smog controls. Strike that: I believe there were some early cars that used a pressure pump on the gas tank to feed gas to the carburetor. But by the 1920s or especially 1930s when mechanical fuel pumps were introduced I think my above statement is correct. Quote Link to comment Share on other sites More sharing options...
The Oil Soup Posted October 15, 2017 Report Share Posted October 15, 2017 The cap I have was purchased this year at Oreillys. Quote Link to comment Share on other sites More sharing options...
NiftyFifty Posted October 15, 2017 Report Share Posted October 15, 2017 59 minutes ago, The Oil Soup said: The cap I have was purchased this year at Oreillys. Throw it out...I bought one of those "vented" caps for mine...had bucking and vapour locking issues whenever it got hot out...finally drilled a hole right through the top and solved those issues, but Id prefer to find the right cap if I could. Quote Link to comment Share on other sites More sharing options...
Branded Posted October 15, 2017 Report Share Posted October 15, 2017 2 hours ago, The Oil Soup said: The cap I have was purchased this year at Oreillys. Us a screw drive or pair of pliers and pull the metal cove off the check valve and remove it. Problem solved Quote Link to comment Share on other sites More sharing options...
NiftyFifty Posted October 16, 2017 Report Share Posted October 16, 2017 Mine was a sealed plastic vent, no way to tamper with it, not sure if yours is the same Soup Quote Link to comment Share on other sites More sharing options...
Branded Posted October 16, 2017 Report Share Posted October 16, 2017 9 hours ago, 4mula-dlx said: Mine was a sealed plastic vent, no way to tamper with it, not sure if yours is the same Soup Why can you remove the plastic vent, can't tell what you have without a picture. Quote Link to comment Share on other sites More sharing options...
Branded Posted October 16, 2017 Report Share Posted October 16, 2017 9 hours ago, 4mula-dlx said: Mine was a sealed plastic vent, no way to tamper with it, not sure if yours is the same Soup If it looks like the just remove the plastic cap and the internals under it. Quote Link to comment Share on other sites More sharing options...
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