Thread: fuel tank vent??

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I have a '39 Ford two door sedan on an '86 S10 Blazer frame, 355 SBC. The previous owner had installed a '68 Volkswagen fuel tank filler in the left rear 1/4 over the rear fender. The fuel neck is a non-vented type so I'm not running a vent. Is this okay? I haven't had any problems so far. There is a third line coming off the S10 sender which I plugged. Maybe I'm second-guessing myself. Thanks in advance, Rod

Are you running an electric fuel pump, or a mechanical? Since you mention "...a third line coming off the S10 sender..." it sounds like it's the stock S10 tank, the stock in-tank electric pump, and a supply & return line to/from the engine? My guess is that the third line was the one to the charcoal canister, which is the tank vent to deal with tank pressure, mainly from changes in temperature. If you open your fuel cap on a nice hot summer day do you hear a "woosh" of pressure relieving?

Hi, and thanks for the comment. Yes, it is the stock S10 tank and I'm running a Holley blue pump. I really haven't heard the "whoosh" but I just got it running in September. I'm just a little nervous that maybe I should provide for a vent, but maybe not. there were lots of cars without them. I just want to be safe.

Originally Posted by raj4851

Hi, and thanks for the comment. Yes, it is the stock S10 tank and I'm running a Holley blue pump. I really haven't heard the "whoosh" but I just got it running in September. I'm just a little nervous that maybe I should provide for a vent, but maybe not. there were lots of cars without them. I just want to be safe.

If it were mine I'd take the plug out of the third line and extend it up to a convenient high point with a loop, leaving it open to atmosphere to vent the tank. The down side is that you might get some minor fuel fumes in a closed garage, but it shouldn't be bad. If that's wrong someone else will jump in and offer their alternative. Since it's a S10 Chassis swap another approach would be to put the evaporator (charcoal) canister back on, wire up all of the solenoids, and have it back OEM.

Hi again Roger, and thanks for the update. I had thought of running a hose from the vent line upwards with a vent for a differential in the end of the hose. Just a thought. Thanks again, Rod

Could do the easy thing, run a vented cap.....

Originally Posted by Dave Severson

Could do the easy thing, run a vented cap.....

i dont remember why but that`s all i did on my V6 pinto .. i just drilled a hole thru the gas cap ..

A vented cap only vents one way, air goes in and doesn't come out.
drilling a hole in the cap will let fumes out of the hole into where ever the cap is.

A few options buy a vented cap or tap the filler neck ( at the top near the cap) and screw in a small 90 degree fitting and plumb to the underside of the car, fumes will come out down there.

Gas expands when hot and will build up some pressure which isn't a big deal, sucking the gas out of the tank and collapsing the tank is a big deal and you will have running issues.

I ran into this on my 53 with a new unvented tank, my car would stumble on the top end because it was starving for fuel, a changed the cap and the stumble went away. I bought a vented 55 Chevy cap
the stock s-10 cap should be vented one way inward. Having a slight woosh ( outward )sound on a hot day is common with a factory modern car ( s-10 ), having a inward woosh is bad.

Godspeed
MrC.

If your sender has 3 ports and you have the vent plugged then I assume you still have the supply & a return ? If that's the case then your fine, as a closed loop system won't need the vent to operate properly. That being said I would keep an eye on it parked in the sun on a hot day and make sure it's not ballooning the tank from the pressure build up.

Originally Posted by MrC.

A vented cap only vents one way, air goes in and doesn't come out.
drilling a hole in the cap will let fumes out of the hole into where ever the cap is.

A few options buy a vented cap or tap the filler neck ( at the top near the cap) and screw in a small 90 degree fitting and plumb to the underside of the car, fumes will come out down there.

Gas expands when hot and will build up some pressure which isn't a big deal, sucking the gas out of the tank and collapsing the tank is a big deal and you will have running issues.

I ran into this on my 53 with a new unvented tank, my car would stumble on the top end because it was starving for fuel, a changed the cap and the stumble went away. I bought a vented 55 Chevy cap
the stock s-10 cap should be vented one way inward. Having a slight woosh ( outward )sound on a hot day is common with a factory modern car ( s-10 ), having a inward woosh is bad.

Godspeed
MrC.

Also a decent fuel pump can suck the sides of the tank in fairly easily

If it is adequately vented the tank can't be sucked in.

Godspeed
MrC.

Hi MrC, and thanks for the input. I actually have a VW gas door and filler, which the former owner installed into the 1/4 panel. I decided to get a rear axle vent and run it up the filler tube from the S10 vent hose on my sender. I think that should work. Again, thanks for the info, Rod

Just a thought--
The 82-92 Camaro / Firebird / Trans Am has 4 lines.
1) feed
2) return
3) charcoal can
4) vent.
The vent is small UFO / cone looking thing.
It hangs off a piece of hose about 4 inches long IIRC.
However, GM has not reproduced it.
There is a revisited thread in another forum. If you are interested, tomorrow after work I can
send you the link.

Hi t-top, and thanks for the info. I just had three lines on the S10 sender so I think I'll be alright. Interesting about those F-bodies, though. Thanks again, Rod

I am not sure where you are in your build, but if expensive interior or long term garage parking is its future ...you might consider the full fuel system vent system.......the smell will get old and seep into the inside from any small holes, after so long it will saturate into the interior materials.

Not mandatory, but certainly will not hurt.......used vapor recovery canisters are a dime a dozen.