The Perils of An Unvented Gas Tank - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 16 (permalink) Old 03-16-2010, 09:47 PM Thread Starter
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The Perils of An Unvented Gas Tank

Four years ago I removed the vapor canister on my 81 280zxt in order to route my intercooler piping. Before removing it, I researched on Zcar and Hybridz the impact of leaving the tank unvented. The research results were 50/50, some saying that leaving the tank unvented would not cause any issues while others suggested adding a vent or tucking a small vapor canister from a different model car in the wheel well (I should have listened Tonyd!!).

I decided I would not initially vent the tank and would monitor the tank when filling, etc for odd behavior. My Z is driven at most 2k miles a year. During that time I only experienced one odd experience when the tank blew a 4 foot stream of gas onto the adjacent gas pump when I cracked open the filler cap. I might add my boost is set at 12 PSI and is fueled by a fuel pump from a Porsche 911 twin turbo.

Last fall, three years after having removed the vapor canister, my Z started experiencing fuel starvation issues. Whenever the gas level dropped below 3/4's the fuel pressure would fall off and it would run lean.

After a very frustrating period of investigation and head scratching, I finally realized what the issue was. When viewed from underneath, it appeared that my gas tank was crushed! Which was even more evident when I dropped it and saw the condition of the top of the tank.

It appears that after an unusually long day of spirited driving to and from Lime Rock Park on our club's annual Bob Sharp Lime Rock day last summer, the vacuum built up in the tank to a point that it permanently deformed the tank, forming an impressive crease in the metal. The heavy fuel pickup tube was bent to the point that the strainer was snorkeling above the fuel level at 3/4 tank. Needless to say, the replacement tank is going in soon and will be vented.






Phil
1981 280zxt
5-speed conversion, 3.9 R200, Eibach springs, Tokico struts, Energy Suspension, K&N CAI, Innovate WB, Cusco Strut Bar, Greddy B Spec II and POV, HKS BOV, 3" mandrel SS exhaust, Magnaflow, Spearco Intercooler, currently 12 psi
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post #2 of 16 (permalink) Old 03-16-2010, 10:25 PM
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Re: The Perils of An Unvented Gas Tank

Wow
I was going to just relocate the carbon canister when I do the intercooler & swap, now I am convinced that is the way to go.
Thanks for posting that & the pictures, very informative!

The capacity of the tank must have dropped but would be hard to notice since you could not run below 3/4 before filling back up.

Orange 77 280z coupe .. Eibachs , Illuminas , Magnaflow Seattle WA
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post #3 of 16 (permalink) Old 03-16-2010, 10:39 PM
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Visual evidence!

Maybe this will finally convince those otherwise that want to "delete all the useless smog stuff." Thanks for the post, and good luck. Hope you get back on the road soon!
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post #4 of 16 (permalink) Old 03-16-2010, 10:42 PM Thread Starter
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Re: The Perils of An Unvented Gas Tank

I initially thought there was a pinhole leak in the fuel pickup tube that would suck air when the fuel level dropped below it. But then I couldn't pull the fuel sender out of the tank and couldn't figure out why!!

Phil
1981 280zxt
5-speed conversion, 3.9 R200, Eibach springs, Tokico struts, Energy Suspension, K&N CAI, Innovate WB, Cusco Strut Bar, Greddy B Spec II and POV, HKS BOV, 3" mandrel SS exhaust, Magnaflow, Spearco Intercooler, currently 12 psi
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post #5 of 16 (permalink) Old 03-16-2010, 10:43 PM
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Re: The Perils of An Unvented Gas Tank

That horror scene will stay in the back of my mind if I ever decide to upgrade to more boost.

Phoenix, Arizona-Going to UTI

1981 280zx turbo-Does not look pretty but runs without a problem.
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post #6 of 16 (permalink) Old 03-16-2010, 10:44 PM
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Re: The Perils of An Unvented Gas Tank

ops and think not venting the gas tank with more boost.

Phoenix, Arizona-Going to UTI

1981 280zx turbo-Does not look pretty but runs without a problem.
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post #7 of 16 (permalink) Old 03-16-2010, 11:25 PM
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Re: The Perils of An Unvented Gas Tank

Phil280zxt Wrote:
-------------------------------------------------------
> I initially thought there was a pinhole leak in
> the fuel pickup tube that would suck air when the
> fuel level dropped below it. But then I couldn't
> pull the fuel sender out of the tank and couldn't
> figure out why!!

Knowing that PRETTY car of yours, it's hard to believe
that something that UGGGLLLY came out of it!!

1969 OLD.Z (#00013 10/69 gold on black) since 8/30/76
1969 ITSA.Z (#00171 11/69 green on black) since 8/24/73 28K mi
1970 ZEE-70 (#06289 6/70 candyapple red on black) original owner
1971 PL-510 2-door (our 160-Z) since 12/31/75
1971 (#19851 1/71 blue
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post #8 of 16 (permalink) Old 03-17-2010, 12:07 AM
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Re: The Perils of An Unvented Gas Tank

My CC and all the smog crap on my car is gone, but I still HAVE a filtered vent line from the line that used to go to the CC from the tank.

Been like that for 7 months or so now.

Porsche Midnight Blue 82 280ZX swapped turbo. SSR LongChamp XR-4s 15x9.5 -33 15x10 -40
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post #9 of 16 (permalink) Old 03-17-2010, 02:11 AM
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Re: The Perils of An Unvented Gas Tank

I have actually seen a gas tank even more crunched up then that from a guy running a non venting cap when his car called for a vented cap. His wife left the cap at the gas station and when she realized what she did she went to the parts store and they sold her the wrong type cap. He didn't know until it was sucked up to less than half its original size. She wasn't allowed to drive his baby anymore.

western Nebraska
1979 280zx coupe parts car
1980 280ZX coupe
1982 280zx,
1971 240z 1st series
2005 pathfinder
1974 & 1977 corvettes
1994 F150 4x4 van works custom pickup,
1998 mustang
2003 350Z
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post #10 of 16 (permalink) Old 03-17-2010, 08:30 AM
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Re: The Perils of An Unvented Gas Tank

Were you running the wrong gas cap, or had it's internal vacuum relief vent frozen closed?

Bob, in San Diego, 83 280ZX Turbo Coupe 5 speed. Visit
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