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Old 09-25-2017, 11:10 AM   #1
6768chevylover
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gas tank pressure

I just got back from a long 211 mile journey to a car show in this nice hot weather were having on the east coast. Found out my speedo is off and that apparently I get major pressure in the gas tank. I drove down to a show on thursday and the temp was around the late 70s early 80s, had no issue.. Went back home yesterday and the temp was almost 90, issue.. I stopped at a gas station to get gas. I had about 1/4 tank left. I open the cap and gas and pressure spit out. It was all highway speeds for both trips. Its a 71 blazer, replacement tank, no return lines, vented to rear tank canister, and tank filler line is kinked a little. I've never had an issue but then I never took it on a long journey like that in the hot sun at constant 70 mph. Any ideas or corrections?
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Old 09-25-2017, 04:32 PM   #2
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Re: gas tank pressure

Sounds like your vent pipe or canister is clogged. Just use a vented cap from a 70 or older model.
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Old 09-26-2017, 11:42 AM   #3
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Re: gas tank pressure

does anyone have a manual picture of the vent lines? only because the PO I got the blazer from had a 50 gal tank in it but it leaked and I replaced it with a 21 gal repro tank.
also on the filler neck, there is 2 lines of course the big line is the gas filler line but then another which is the filler vent line. Where does that attach to? I'm sure to tank next to filler spout.
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Old 09-27-2017, 01:50 PM   #4
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Re: gas tank pressure

mine does that because the PO replaced the tank and didn't have the old neck put on the new tank. It has a hose that collapses. I have to drop the tank and have the old neck put on
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Old 09-28-2017, 11:09 AM   #5
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Re: gas tank pressure

Is there an issue with blowing some air into the canister to mix things around?
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Old 09-28-2017, 11:40 AM   #6
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Re: gas tank pressure

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Originally Posted by 6768chevylover View Post
Is there an issue with blowing some air into the canister to mix things around?
It's charcoal, so nothing to move around. The canister is over 45 years old assuming it's never been replaced, so chances are it's lost it's ability to soak up fuel vapors. Just put a vented cap on and be done with it. Doing this will basically bypass all the EVAP system that most likely doesn't work anymore.
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Old 09-28-2017, 12:25 PM   #7
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Re: gas tank pressure

Hemi, Should I use an earlier cap w/o eec?
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Old 09-28-2017, 12:59 PM   #8
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Re: gas tank pressure

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Hemi, Should I use an earlier cap w/o eec?
Yup, like I mentioned in my first post, use a 1970 or older gas cap.
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Old 09-28-2017, 02:35 PM   #9
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Re: gas tank pressure

Thanks..
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Old 09-29-2017, 12:02 PM   #10
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Re: gas tank pressure

wow, I actually had a vented gas cap on my truck all this time. What could I do to fix this problem?
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Old 09-29-2017, 12:43 PM   #11
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Re: gas tank pressure

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wow, I actually had a vented gas cap on my truck all this time. What could I do to fix this problem?
If your tank "spit out" pressure, and you have a vented cap, then the cap is faulty. Clear the obstruction in the vent hole or buy another cap. It ain't rocket science !!
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Old 09-29-2017, 02:46 PM   #12
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Re: gas tank pressure

LOL.. Understood. 3 times the charm Hemi..
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