Question about gas caps...

[trapin]

What determines if you'll need a vented or a non-vented cap?

My drivetrain is LS1 with fuel injection and I'll have a Walpro pump mounted inside the stock gas tank. The filter will be Corvette and have a return to the tank.

Thanks.

[mdprovee]

I think it depends on if your tank has a vent line or openning for a line, or not.

Not sure.

[parsonsj]

Yes. You need venting to allow fuel to flow to the engine without the tank drawing a vacuum.

It is useful to have venting to aid in filling the tank, but that's not required.

If your tank is vented, use a non-vented cap. If your tank is not vented, you must use a vented cap.

jp

[trapin]

I just found out that it is not vented...so the cap will need to be.

Thanks guys. Just doing some investigating right now.

[2yellow69]

Vented caps are VERY important if your tank is not vented!! Our gas cap was stolen off our 69 Camaro at a car show of all places. I went to Checker's for a new one and put it on. Over the next few weeks of driving the car every day, my neighbor and I were running outside once every night because it sounded like someone was throwing a baseball at the car. I also thought my fuel gauge was going bad because I would run out of gas at about 1/3rd of a tank. It turns out that my new non-vented cap on my old non-vented tank was causing the top of the tank to suck itself down about 3 inches and bend the fuel pickup. When it cooled down at night the sound we were hearing was the tank popping somewhat back into shape! Just shows how strong a standard fuel pump feeding a V-8 2bbl really is. Moral of the story is that I had to replace the tank, straps, fuel sender and of course the cap!!
Matt

[dsapper]

how can you tell if the cap is vented or not? I bought a replacement from checkers a few days ago that looks very close to the one that was already on my 69 camaro, the S shaped one.

I'm replacing a fuel tank/sending unit tomorrow and dont want to go through what you did 2yellow69.

And its funny because I was replacing all this because the bottom of the gas tank was caved in and bent the sending unit. I just thought some jackass before me jacked up the car with the tank or something but I'm wondering now if this is the cause? The gas gauge didnt work btw.

[2yellow69]

I don't know how you would test it. I went to NAPA and told them what I needed. Haven't had a problem yet(it's been 3 years).
Matt

[dsapper]

I would hope I was given the right cap but at these new parts stores its amazing you get anything right. You ask for fuel lines or a thermostat for a sb chevy and they ask you what year the car is and make/model lol.

[Midnight68]

Don't most newer fuel injected cars have non vented caps and are vented elsewere. I am switching to an LS2 so is a vented cap ok or should I add a vent from the tank itself and use a non-vented cap?

[2yellow69]

I once had a guy ask if I had power locks when I asked for a starter for a 69 Camaro. Was that even an option back then?
Hey Midnight68; It's your favorite guy with a yellow 69(and a mil-spec .45). And when are you gonna get that 4l80e out of my garage?
Matt