If you look at the oem o-ring closely you'll see that the edges are sort of squared off. I replaced mine with a generic o-ring from the hardware store which has a more traditional rounded edge. When installed the outer edge of the ring sticks out just a tad further than the stock one. This makes for a very tight seal. You'll notice how tightly it seals when screwing it in. I'm pretty sure the o-ring I used is 1/4" but it's been awhile so I'm not 100% positive.

You can also try wrapping the threads of the screw with teflon tape.

romeen said:

If you look at the oem o-ring closely you'll see that the edges are sort of squared off. I replaced mine with a generic o-ring from the hardware store which has a more traditional rounded edge. When installed the outer edge of the ring sticks out just a tad further than the stock one. This makes for a very tight seal. You'll notice how tightly it seals when screwing it in. I'm pretty sure the o-ring I used is 1/4" but it's been awhile so I'm not 100% positive.

You can also try wrapping the threads of the screw with teflon tape.

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Don't really know what you mean by squared edges, the oring I got ([MD614948]) looked like a simple oring. The teflon doesn't sound like a bad idea though.
Anyone else?

I use the teflon tape on everything that has threads. i.e. blow-off valve,biss,mbc,ect..

Teflon tape is for toilet plumbing. Keep it away from your car. Use an automotive product for those threads.
For the BISS, adjust it, spray in WD-40, dab out any liquid and fill with silicone seal. The WD-40 will make it removable.

romeen said:

If you look at the oem o-ring closely you'll see that the edges are sort of squared off. I replaced mine with a generic o-ring from the hardware store which has a more traditional rounded edge. When installed the outer edge of the ring sticks out just a tad further than the stock one. This makes for a very tight seal. You'll notice how tightly it seals when screwing it in. I'm pretty sure the o-ring I used is 1/4" but it's been awhile so I'm not 100% positive.

You can also try wrapping the threads of the screw with teflon tape.

Click to expand...

+1 for teflon tape. make sure you do a good clean wrap though, dont want any coming off and being sucked into the intake.

Defiant said:

Teflon tape is for toilet plumbing. Keep it away from your car. Use an automotive product for those threads.
For the BISS, adjust it, spray in WD-40, dab out any liquid and fill with silicone seal. The WD-40 will make it removable.

Click to expand...

Thank you very much, all of you... this seems like the best way though.

Defiant said:

Teflon tape is for toilet plumbing. Keep it away from your car. Use an automotive product for those threads.
For the BISS, adjust it, spray in WD-40, dab out any liquid and fill with silicone seal. The WD-40 will make it removable.

Click to expand...

I disagree. Teflon tape has been successfully used in many applications outside of plumbing with good results. There are higher grades which are resistant to gasoline if that's what you mean.

If air is leaking past the BISS then certainly WD-40 will be able to seep past it and into the TB. Once there it can trap particulates and form a sludge-like material that may partially block the air passage that is controlled by the BISS screw.

WD-40 in TB

eboy0 said:

Has anyone ever had the problem of their biss screw just leaking boost no matter what? I replaced the oring and the screw, got it from JNZtuning. Leaked as soon as I got my idle right. Put the cap on, next time I opened the hood cap was gone..... so i thought maybe i need another oring, same thing.
What do you guys do? Maybe I'm not installing the oring properly? Are you supposed to grease it up or something? Also, I really don't want to silicone up the hole, since I may need to adjust the biss in the future, anyone have any tips?

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Get an o-ring that is slightly thicker than the one you have, apply DIELECTIC GREASE, slowly and carfully turn it in. No need for taflon or RTV.

oldman said:

Get an o-ring that is slightly thicker than the one you have, apply DIELECTIC GREASE, slowly and carfully turn it in. No need for taflon or RTV.

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Agreed. That's what I was trying to say in post #2. The 1/4" o-ring will be just a little bigger than the stock one and make a very tight seal. Any hardware store should have them.

romeen said:

I disagree. Teflon tape has been successfully used in many applications outside of plumbing with good results. There are higher grades which are resistant to gasoline if that's what you mean.

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Pulling a thread of that crap out of an oil gallery just one time may forever alter your recommending its use. I don't make recommendations based on advertising.

If air is leaking past the BISS then certainly WD-40 will be able to seep past it and into the TB. Once there it can trap particulates and form a sludge-like material that may partially block the air passage that is controlled by the BISS screw.

WD-40 in TB

Click to expand...

Holy crap, how much do you plan on using? Give it a squirt, daub the liquid out with a Q-tip, fill the hole with silicone seal to make a plug that fits tightly and conforms to the cavity while locking the BISS screw in place. No air's getting past it. The WD-40 is only to prevent the silicone from getting adhesion to the screw and threads.
If there's enough crud around your TB to form a "sludge-like material", there's deeper issues than a vacuum leak.

Defiant said:

Pulling a thread of that crap out of an oil gallery just one time may forever alter your recommending its use. I don't make recommendations based on advertising.Holy crap, how much do you plan on using? Give it a squirt, daub the liquid out with a Q-tip, fill the hole with silicone seal to make a plug that fits tightly and conforms to the cavity while locking the BISS screw in place. No air's getting past it. The WD-40 is only to prevent the silicone from getting adhesion to the screw and threads.
If there's enough crud around your TB to form a "sludge-like material", there's deeper issues than a vacuum leak.

Click to expand...

I never recommended using teflon tape on any screw that is involved with an oil passage. I have however used it successfully on the adjustment screw of my AFPR as recommended so I feel that it does have it's place in automotive applications. There are posts here on the forums from guys having used it on their leaking BISS screws with good results. Personally, I replaced my o-ring with a 1/4" one (as mentioned above) which was just enough larger in diameter to make a very tight seal and this is what I maintain is a cheap, easy fix.

I don't plan on using any WD-40. I think it's a great product. But if air can leak past the screw then the capillary action of the penetrant should allow it to seep past the threads in the opposite direction. In fact, under vacuum it will probably get sucked past. When the lighter components of the penetrant evaporate it leaves a residue which, as many have probably noticed, practically acts like a magnet for small particulates (dust, etc.).

Defiant, I actually think you have a lot of very useful pearls and I respect your input to the forums. In fact, I look forward to reading your posts not only for the helpful content but also for the unique "tone" of the comments. But on this one issue I still disagree and stick with my original suggestion as I think it will be more effective and has no downsides that I can see.

romeen said:

Agreed. That's what I was trying to say in post #2. The 1/4" o-ring will be just a little bigger than the stock one and make a very tight seal. Any hardware store should have them.

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Agreed! We do assembly of high pressure hydrolic tanks where i work. Every o ring has lubricant b4 install. It leaks if installed dry during pressure testing.

Best answer right there

That best answer right there, is almost 9 years old..

Didnt even look at the age.

They make PTFE thread sealant that is basically liquid teflon tape.... and it's what sealed the 25 year old BISS on the 90 TSI AWD I just sold...

It's the same sealant we use on AN to not adapters when mating them to a fuel or hydraulics system.