Vented fuel cap..

Glatt

Daily Driver
Nov 13, 2008
47
0
0
Lethbridge, Alberta, Canada
When I modified my tank and lines to create the return fuel system needed for my engine I didn't have a way to vent the tank properly. Does anyone know of an aftermarket fuel cap that vents at a certain pressure? I have to leave the cap a little loose as it sits or the pressure in the tank gets huge..

Any direction would be great...

Arthur
 

brrymnvette

Frequent Racer
Oct 18, 2004
316
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St Louis, MO
We've just drilled a very small hole in the cap before. Just had to do it about a month ago to my buddies twin turbo viper. We did a 3/16" bit and it worked perfectly.
 

Deuce4935

Frequent Racer
Nov 19, 2007
341
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Chicago, Il
Whats th epurpose of the vented cap, and how do you know if you need one? Sorry for the threadjack.
 

Glatt

Daily Driver
Thread starter
Nov 13, 2008
47
0
0
Lethbridge, Alberta, Canada
I will try that out.. Thanks
brrymnvette said:
We've just drilled a very small hole in the cap before. Just had to do it about a month ago to my buddies twin turbo viper. We did a 3/16" bit and it worked perfectly.
 

Glatt

Daily Driver
Thread starter
Nov 13, 2008
47
0
0
Lethbridge, Alberta, Canada
The vented cap will bleed off any pressure caused by the fuel being pulled and recirculated back into the tank, or let air into the tank if a vacuum is created. Some engines will pull enough fuel to create a vacuum in the tank at WOT. I am having an issue with over pressurizing I think because of the return fuel system I have

When I unscrew the cap to fuel up, I can hear a huge amount of air being sucked into the tank.. A little bit of pressure is alright but I have WAY too much.

Deuce4935 said:
Whats th epurpose of the vented cap, and how do you know if you need one? Sorry for the threadjack.
 

Deuce4935

Frequent Racer
Nov 19, 2007
341
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0
Chicago, Il
Could that be the reason why sometimes when im fueling up, the fuel will spit out the filler tube and the tank isnt full yet?
 

Glatt

Daily Driver
Thread starter
Nov 13, 2008
47
0
0
Lethbridge, Alberta, Canada
Deuce4935 said:
Could that be the reason why sometimes when im fueling up, the fuel will spit out the filler tube and the tank isnt full yet?

That could be part of it for sure..

I pulled my cap apart last night ( separated the screw plastic from the top grip plastic) and drilled through the middle of the screw in part with a 1/4" drill bit. There are a bunch of springs and guts inside I chucked in the garbage bin and the car vents perfectly now.. You can't tell I didn't anything to it either, that's the way I like it. ;)
 

LS6 Tommy

MalibuRacing Junkie
May 15, 2004
15,847
1
38
North Jersey
brrymnvette said:
We've just drilled a very small hole in the cap before. Just had to do it about a month ago to my buddies twin turbo viper. We did a 3/16" bit and it worked perfectly.
Glatt said:
I will try that out.. Thanks

You'll dump gas every time you get on it hard. The Viper doesn't have an issue with that as the fill cap is up above the tank & not parallel to the ground on the back of the car.

Glatt said:
I am having an issue with over pressurizing I think because of the return fuel system I have

When I unscrew the cap to fuel up, I can hear a huge amount of air being sucked into the tank.. A little bit of pressure is alright but I have WAY too much.


Air being sucked into the tank indicates a vacuum condition, not a pressure condition.

Tommy
 

1980PontiacWagon

Frequent Racer
Feb 5, 2011
686
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16
Northern Virginia
I'm having the same problem. Glatt was your cap stock or locking? I have a locking cap....don't need anyone messing around with my gas...since its $4.00 a gallon for 93.
 

Randy W

Frequent Racer
My '67 Impala SS with the LT1/4L60E swap had the problem and the cap was too low to just drill and there wasn't a direct fit vented cap for it that I could find. So I drilled the middle 1/4", reamed the hole until 1/4" tubing would go in with a lot of persuasion. I then bent a loop on the tank side of the tubing so gas couldn't just run through it then on the outside I bent it gently up until it was flush with the lid. My cam was metal so I soldered the tubing in place as a precaution. Never got a drop of gas and cured my suction problem.
 

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