Slant Six Forum :: Gas Stench

Remember also that there's a sound deadener mat between the top of the tank and the underside of the trunk floor, which does a great job of absorbing water and, over the years, rusting the top of the tank. You may wind up pulling the tank to inspect it all over for leaks.

Be sure to check the fuel gauge sender gasket; they can get to seeping or weeping over the years...

WHAT?! I CAN'T HEAR YOU! I'VE GOT ZZTOP PLAYING ON MY iPOD!

An iPod is the Apple MP3 player I wish I had but don't feel like buying, having just bought a new computer late last month.

And yeah, of course it's playing "Manic Mechanic". What other tune contains the Chrysler gear-reduction starter sound? (Well, OK, I can think of at least one other...can you?)

"No Parking on the Dance Floor", by Midnight Star. Right at the very beginning of the track.

Author:	Dennis Weaver [ Fri Jan 21, 2005 2:57 pm ]
Post subject:	Gas Stench
This dilemma pertains specifically to my '69 Newport convertible but the logic and possible solutions would apply to slant six cars as well... Being a '69, the fuel system is pretty simple. One very large gas tank, rear fill, two vents coming out of the upper left forward part of the tank, one runs up into the shock crossmember and turns down, the other goes up into the trunk, weaves around then turns down into the frame rail. A two-piece fuel line runs the length of the car down the passenger side with a short rubber hose connecting them under the pass door. A standard mechanical fuel pump supplies fuel to a Carter AVS four-barrel. Here's the problem, I'm hoping one or more of the big brains here can help solve this one: In the last couple months when I'm out on warm days cruising around, I smell a lot of gasoline vapors around the rear of the car when I shut it off. This is particulary bad when I pull the car in the garage under my house, I have to wait awhile for the fumes to dissipate before I can close things up. I have checked and replaced all of the rubber hoses at the tank and elsewhere. The only thing that even looked a little suspicious were the hoses at the tank vents, and now they are replaced. All of the metal lines have been inspected and re-inspected. A few years ago, the forward main body line developed a leak when it rusted thru from the outside. I replaced it and have double checked it - checks OK. There don't appear to be any leaks at the tank or the sending unit. I have tried vented and non-vented caps (non-vented is standard for this year). A couple things... I freshened and hopped up the motor a little about 4 months ago (yep, just did a hone job and put rings and rod bearings, cam, lifters and timing set in it, even put the same heads back on that had been done some time before I got the car - a sleazy "build" with the motor in the car SUE ME! ) At that time I replaced the fuel pump with a NORS unit I purchased for cheep. It was supposed to be a Carter, but all I kept getting from this guy was reboxed stuff, so it's an Airtex, not my favorite, but as good as what Idiot Auto Partz sells. I noticed the other day when I pulled it in it sounded like the vent was gurgling. It stopped when I loosened the cap, but there was no "whoosh" of air. Today, when I got out to manually open the garage door (I don't need no stinkin' opener!) There was a very small puddle of gas left in the driveway, about where the front of the tank had been situated, but I could find no evidence of gas anywhere on the car when I crawled up under. The only thing I can imagine is that the pump is bleeding pressure back to the tank, and it's spitting out the vent(s). I have several other NORS pumps I can try. Any suggestions before I needlessly swap fuel pumps? Stumped, D/W

Author:	SlantSixDan [ Fri Jan 21, 2005 3:31 pm ]
Post subject:
I think you'll find your trouble is with the tank or the vents, not with anything closer to the front of the car. The fuel pump can't really "bleed pressure back to the tank"—if the pump has a less-than-perfect valve seal, the gasoline can drain back to the tank, but just by gravity. No pressure reaches the tank via the pump. The symptom of that is extended crank time after sitting. Don't recollect where you're located, but if you fill the tank when it's cool out (morning, evening) then the car warms up (e.g. in the sun), the gasoline will expand and if the tank's full, it'll drain right out of the vents and onto the driveway. Remember also that there's a sound deadener mat between the top of the tank and the underside of the trunk floor, which does a great job of absorbing water and, over the years, rusting the top of the tank. You may wind up pulling the tank to inspect it all over for leaks.

Author:	Dennis Weaver [ Fri Jan 21, 2005 3:39 pm ]
Post subject:
Quote: Remember also that there's a sound deadener mat between the top of the tank and the underside of the trunk floor, which does a great job of absorbing water and, over the years, rusting the top of the tank. You may wind up pulling the tank to inspect it all over for leaks. You're right, I had thought of that. Thing is, it doesn't stay out in the weather at all in the 3 years that I've had it, and the problem just developed. Still, there is a lot of rust in the trunk, so that's a very real possibility. No bad gas smell in the trunk, though, and there's plenty of "ventilation" for it to get in if the tank had a hole in the top. Only one way to find out for sure, huh? I had dual exhaust run about the time I sealed up the motor, one pipe is fairly close to the tank (by a couple inches, meaning). Suppose that could be warming up the gas in the tank enough to cause pressure in it? D/W

Author:	SlantSixDan [ Fri Jan 21, 2005 3:43 pm ]
Post subject:
Full tank plus nearby exhaust pipes? Definitely! The factory put in heat shielding in such instances. Make sure the tank vents themselves are free and clear, too.

Author:	Dennis Weaver [ Fri Jan 21, 2005 3:46 pm ]
Post subject:
The tank's not full, though... Mebee three quarter tank rite now. I will consult the '69 Parts book and see what shielding is called for, if any, on dual exhaust cars. I don't recall ever seeing it on any of the factory dual cars I've owned, but that doesn't mean it never existed. D/W

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Author:	SlantSixDan [ Fri Jan 21, 2005 4:02 pm ]
Post subject:
Gas smells with a ¼-full tank point to a tank or lines leak.

Author:	Dennis Weaver [ Fri Jan 21, 2005 4:07 pm ]
Post subject:
I said 3/4 tank... Is that still what you think? D/W

Author:	SlantSixDan [ Fri Jan 21, 2005 4:30 pm ]
Post subject:
Quote: I said 3/4 tank WHAT?! I CAN'T HEAR YOU! I'VE GOT ZZTOP PLAYING ON MY iPOD! Yep, what I meant was that fuel stench with less than a full tank tends to point to leak(s) in the tank and/or lines. Be sure to check the fuel gauge sender gasket; they can get to seeping or weeping over the years...

Author:	Dennis Weaver [ Fri Jan 21, 2005 4:44 pm ]
Post subject:
Quote: Be sure to check the fuel gauge sender gasket; they can get to seeping or weeping over the years... Good point, and one of the first things I checked. D/W

Author:	SlantSixDan [ Fri Jan 21, 2005 4:57 pm ]
Post subject:
An iPod is the Apple MP3 player I wish I had but don't feel like buying, having just bought a new computer late last month. And yeah, of course it's playing "Manic Mechanic". What other tune contains the Chrysler gear-reduction starter sound? (Well, OK, I can think of at least one other...can you?)

Author:	Dennis Weaver [ Fri Jan 21, 2005 5:03 pm ]
Post subject:
Quote: An iPod is the Apple MP3 player I wish I had but don't feel like buying, having just bought a new computer late last month. And yeah, of course it's playing "Manic Mechanic". What other tune contains the Chrysler gear-reduction starter sound? (Well, OK, I can think of at least one other...can you?) 3) Jan and Dean/"Drag City"? I dunno, can I use a lifeline, Regis? D/W

Author:	SlantSixDan [ Fri Jan 21, 2005 5:35 pm ]
Post subject:
"No Parking on the Dance Floor", by Midnight Star. Right at the very beginning of the track.

Author:	Dennis Weaver [ Fri Jan 21, 2005 5:37 pm ]
Post subject:
Quote: "No Parking on the Dance Floor", by Midnight Star. Right at the very beginning of the track. I remember that particular tune from my college daze, but not the nyeeeernyeeeeernyeeeeer sound effect! But I believe you D/W

Author:	Dennis Weaver [ Sat Jan 22, 2005 2:55 pm ]
Post subject:	Update
I've pretty much located the source of the fumes and drips to the short vent tube. I removed and blew thru both tubes, then blew back through the tank, and sure enough, when I pressurized the tank (lung pressure), I got that familiar gurgling sound from the other day out of the other vent. From what I have determined looking inside an identical '69 tank that I have out, one vent is for the front of the tank, and the other runs through the tank to vent the rear, I would assume this is to always have an adequate vent when the gas is at an angle and covers up one vent. Anyway, that all seems to be functioning correctly, no evidence of leaks anywhere (but didn't drop the tank - no stains on tank, and since I did have drops of gas in my driveway yesterday, I'm 90% confident there is no gas coming from the top of the tank). So the tank is pressurizing, forcing a small amount of condensated gas out of the vent tube. Question is, why? Well, I did fail to mention that the weather varies wildly here day to day in the winter. The gas usually stays pretty cold in the tank, even if it's warm enough to drive with the top down in the afternoon. Now to the exhaust pipe. Just like everything else here where I live (and I'm sure lots of other places, too), you just about can't find a decent exhaust shop. The one I went to (private business, not a chain) used to have an excellent reputation, but when I took this car, some toothless redneck with a cigarette dangling from his mouth did all the work, and it was a rush job (for him, not for me) - get him in, get him out, get his money... Anyhow, the pipe on the driver's side is a pretty good distance from the tank, except in one place near the forward corner of the tank, here it is one inch away. Well, I'm not screwing with taking it back and dealing with them again to have it rebent, so I have done the next best thing - Where I work, we throw away scraps of this really nice 1/4" adhesive backed, foil faced foam insulation. I grabbed a piece of it and trimmed it to shape, cleaned the tank up real good in that spot and placed some insulation. Time will tell if this helps, if not, I don't have any idea what I will do next. By the way, Dan, after checking the '69 Service manual and parts book, I don't see where any '69 dual exhaust cars had any special heat shielding at the tank. There is a large flap on the driver's side of the tank, extending from the seam where it is welded together, this appears to shield the tank from the pipe as it turns down over the axle past the tank. Dan, I know you pride yourself in being a source of emissions control trivia. I plan to eventually change the tank, since the the one in the car is pretty bent up on the bottom. The tank I have is from a '71 C-body. I know it will interchange, but I was wondering about the inner tank inside the tank. It has its own little plug in the top and a sticker advising to drain the inner tank when removing the tank for service. What is the function of this inner tank? D/W

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