Drill 2 holes in gas cap to vent it?

[Paul Franssen]

Hi!
I (had to remove) the charcoal cannister in the starboard rear wheelwell some time ago, and I plugged the two rubber hoses with custom made plugs.

Now, each time I take off the gas cap, air rushes into the gas tank, because that tank is no longer vented, as my gas cap is not of the vented variety.

As a solution, I wonder if I might drill a very small hole in the center of the bottom of the cap, and a small hole in the top of it. It would be vented, then, right? Maybe I should offset the two holes so they would not exactly line up, to avoid spillage of gas?

Does any one think there is a drawback to doing that? I wouldn't believe it would spill any gas, would it?

Would vented gas caps for Porsche 911's be readily available (I don't really want to order one from the USA!)

Thanks for your advice in case any one thinks this is a clear "no no" !

[RoninLB]

sounds like a good idea to me.. why not just open the plugged canister lines?

[Paul Franssen]

Thanks your reassuring comment, Ronin.
I would prefer to keep the old canister lines well plugged because they are located in the wheelwell and, conceivably, they might collect muck and water, which might flow down into the insides and stagnate there...whatever.
I think I'll go the vented cap way, either by drilling little holes or if I can find a "professional" vented cap that fits (but I doubt that I can find one quickly).

[RoninLB]

when I removed the gas expansion black plastic tank under the LF fender I took a vent line off and circled it a few times and then tie wrapped it, and hung in high under the fender. I have to try real hard with a very full tank and tight turns to get any leaking.

I like the gas cap holes 'cause it's a little higher and less hose.. please up-date this thread if you drill the cap.... I like your idea.

[jevvy]

will drilling holes not just make yr fuel evaporate over time - this must be a bad thing?

I guess although it "vents" to the canister it is still a sort of sealed unit

I only make this comment as I had a jar of fuel on a shelf and the cap must have been loose, when I went to use some of the fuel a short while later half of it had gone and the rest looked like hangover wee(very yellow)

[k9handler]

Paul,
I would think it would work and the holes could be very small and still be effective, maybe even place them on the side so if any fuel did manage to come out it would flow down the side and through the over spill area.

[Paul Franssen]

Ronin, of course your solution of making a loop with the rubber hose is simple and therefore brilliant. But I can't do that, because I used my Swiss army knife to cut it nice and short...
And I see you are trying to use me as a test case on the drilled cap program

I tend to agree with our K9handling buddy that (the smallest possible) holes should be quite sufficient to vent the tank, however I cannot drill in the side of the gas cap because, when you look at a Porsche screw-in type cap, any hole on the side of it (w)(c)ould, I reckon, be physically blocked-off sideways by the very tube it is screwed into (wow, what language ). My plan right now is to make one (smallest metal drill I have) hole near the center of the bottom, and another one try more off-center in the top (of the screw-cap), and I'd be really surprised if any full-tank sloshing around would spill much over just a few drops (with such small holes not exactly lined-up on both extremes of a hollow body), and any spillage would -any case- end up inside the plastic filling receptible (the square boxlike thing which is built into the wing) to be jettisoned ...

As to evaporation, well, of course that would appear to be a factor, but then, how are purpose-built vented gas-caps any different in preventing evaporation???

Again, thanks guys! Once I've done the drilling (next weekend) and run the car a few times, I'll update on the outcome.

[RoninLB]

Originally posted by Paul Franssen

Once I've done the drilling (next weekend) and run the car a few times, I'll update on the outcome.

after a little more thinking... the cap is sitting at an angle.. so wouldn't 1 interior/gas side small hole drilled at the lower area allow gas to return to the tank without pooling inside the cap ?

[Rot 911]

You will need to vent the gas tank because that whoosh is telling you a vacuum is building up in the gas tank which will lead to fuel starvation. You really don't need a very large hole. Your smallest drill bit will get the job done nicely.

[RickM]

If you're in an emmision controlled state where they check your gas cap you'd fail. Here in NJ they check the cap for sealing integrity. If it leaks you fail. Evaporation may create a less than desirable fume build up plus it's apparently not good for the environment.

There are smaller aftermarket charcoal canisters on the maket that you may be able to fit. Ron's loop idea is pretty cool too.

[jevvy]

...if your not bothered about evaporation then what about Incy Wincy spinder and his mates heading in for a petrol sniffing session - bet you havent considered that

[klaucke]

I have a dirt bike with a custom (read: home) made cap that I vented with a simple hole, and even with gas real close to the cap and rough off road riding, I never found gas seepage to be a problem. Its been a while, but I actually can't remember any gas ever coming out the hole, which was through aluminum that was about 1/2 inch thick.

[RoninLB]

Originally posted by jevvy

what about Incy Wincy spinder and his mates heading in for a petrol sniffing session

that would have to be a real horror show mutated spider to get loaded on gasoline vapors.

fwiw all boats have open venting tanks.. there's even an overfill drain that dumps into the water. Special precautions when up-gassing are in Coast Guard text.

[Paul Franssen]

OK - no need to wait for the weekend to drill 2 holes!
I did it yesterday, 3 mm metal drill, one hole at the very center of the top (straight thru the red plastic cover of the tank cap), and one hole on the bottom surface, off very near the edge.
I'll be driving my car over the weekend and see if the tank vents, and report back.

[Chuck Moreland]

Holes work for venting, but they are a rollover hazard.

Use a check valve to provide one-way air flow. Here is what I did:
Need to vent, my gas tank

[rw7810]

This is exactly what I did. Instead of top, put hole on side where it's not as noticible.

[widebody911]

I had to do something like this on my VW bus. The repro caps are not made the same way as originals, and as such wouldn't vent. I could only get a few miles before the negative pressure in the tank was > what the fuel pump could overcome, and I'd 'run out' of gas. I used the tiniest bit I could find, and that was sufficient.

[Mark sP]

FWIW early 80's VW golfs had a vented cap with the same threaded design. Try a VW dealer

[Formerly Steve Wilkinson]

Friend of mine had an airplane--same kind of airplane as mine at the time, a Falco--and his tank vent line got plugged or collapsed, can't remember which. Granted it was an aluminum tank, not steel, but the fuel pump collapsed the tank totally. Not a good thing to leave them unvented...

Stephan

[Paul Franssen]

Update report:
Well, I drove some (if only 70 or so miles) and took off the gas cap with the two small drilled holes.
It vents, all right, and no spillage...it seems to be adequate.


I do admit that some solutions offered by others are more elegant, and - more importantly so- safer in case of overturning the car (Chuck Moreland)...