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What is the best way to seal O2 to downpipe? Gasket, flange, or nothing?

Posted by Rice Over Wheat, Apr 30, 2007

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  1. Rice Over Wheat

    Rice Over Wheat Proven Member

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    Winter Park, Florida
    I've been battling an exhaust leak from my O2 housing to dp seal and I can't fully eliminate it. The fitment is fine, the surfaces appear machined well, and I can fully torque the bolts down, but still some exhaust gas leaks through. I've tried standard metal layer composite gaskets but I blow them as the composite just burns away, leaving the metal layers and a small gap where the composite used to be. RTV can't hold up to the heat. I'm running bare no gasket now like many people do, but that's not getting me a perfect seal.

    I've searched many vendors and I can't find any kind of crush gasket, like preferably a copper one since copper's melting point is 1083*C. I've considering a 5/16" universal steel flange, but I think that will just cause more problems because then I'll have two mating surfaces instead of one to worry about. Welding them together is out of the question...I really don't want to have to drop my O2 housing to get my exhaust off.

    I'm using a Punishment O2 and a Megan dp, 2.5" at the flanges. How are you guys getting a good 100% seal at that joint? I'm open to any ideas because I'm stuck.
     
  2. romeen

    romeen DSM Wiseman

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    Vancouver, Washington
    I am surprised that you are burning through your gaskets, I didn't think it should get that hot at that location. Do you have any idea what your EGT's are? Nonetheless, I had an exhaust leak at the same location but I think that is because I have an EVO 3 O2 housing with a standard (Buschur) DP so the flange angles don't match up correctly. I used some Ultra Copper RTV on both sides of the gasket last summer and it is holding up fine.
     
  3. DROOPY209

    DROOPY209 Proven Member

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    NorCal, California
    Is your DP also bolted down to your engine?
     
    DROOPY209

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    1992 Eagle Talon TSi AWD
    manual · 1G DSM
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  4. DSMunknown

    DSMunknown Proven Member

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    Yeah, I too was going to suggest that earlier, but I assumed Kevin already tried the copper sealant.



    Here Kev, I found this site using Google. ;) Sure, it's primarily a WRX vendor, but I'm sure the gasket won't mind. :p
     
  5. Rice Over Wheat

    Rice Over Wheat Proven Member

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    Winter Park, Florida
    Bolted down to the engine? It's all properly installed and secured with hangars, etc, if that's what you mean.

    My flange angles aren't perfect either but the flex section should account for that variance. No idea about my EGTs...I got rid of that thing. I heard that there is such thing as aircraft grade RTV that can take much hotter temps than automotive grade. If anyone has seen a copper gasket for exhausts, I'd really appreciate the link.

    I blew out the gasket on a really hard manumatic pull I was doing for a log. I'm kind of surprised there's that much pressure from exhaust gas on the way out of the car.
     
  6. jking29

    jking29 Proven Member

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  7. gsxtacy

    gsxtacy Proven Member

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    Clovis, New Mexico
    You guys are pretty funny~

    Here is what I use:
    DSC04706.jpg
    Straight off the shelf at the local Advanced Auto parts.
    I had to dig around in the back (with a rep of course) to find exactly what I needed.

    And it all boils down to a Ceramic Impregnated Felpro donut gasket for a....:rolleyes: I cannot remember, either a 77 F250 460 Ford Truck or 77 Dodge D150 with a 7.2L

    Anyhow, it works great, seals up great, costs $2.43 to replace and they have tons in stock.
     

    705  0

    1998 Mitsubishi Eclipse GSX
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  8. Boosted98gsx

    Boosted98gsx Proven Member

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    Goop some high temp orange silicone on that thing and you're golden.
     

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    1998 Mitsubishi Eclipse GSX
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  9. Rice Over Wheat

    Rice Over Wheat Proven Member

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    Hey thanks everyone, those last several options sound great and I'm definately going to try them. Very much appreciated!
     
  10. Dream On

    Dream On Proven Member

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    Athens/Oxford, Ohio
    Copper RTV can definitely hold up to the heat. It's sitting between my turbo and manifold with no leaks, without any real gasket.
     
  11. dsm-onster

    dsm-onster DSM Wiseman

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    Are you running a flex pipe or a flex section of some sort som ewhere early in the exhaust?

    It;s possible that your engine is "torquing" and loosening the connection at the o2 housing. . . It's happened w/ me. until I welded up my motor mounts. I didn't know what was happening until I welded the mounts.
     

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  12. Rice Over Wheat

    Rice Over Wheat Proven Member

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    Winter Park, Florida
    I have a megan dp...it has the flex section in the normal spot. I have all brand new mm's, however they are oem, not even polys since I didn't want the really harsh idle on 272s.

    I'll try one of those ceramic gaskets with copper RTV and see how that works.
     
  13. Rice Over Wheat

    Rice Over Wheat Proven Member

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    Winter Park, Florida
    Just wanted to update because I think I fixed it for good. I went to Advanced and got a Felpro gasket for some kind of V8 Ford, made of two metal layers and composite, BUT it was thick and had that steel o-ring insert that keeps the heat from burning the composite layer. Looks just like gsxtacy's pic above. I copper rtv'd both sides and finally eliminated my remaining leak. Thanks for the advice all!
     
  14. gsxtacy

    gsxtacy Proven Member

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    :rolleyes: sweet.

    did I get some rep for all that effort or what?
     

    705  0

    1998 Mitsubishi Eclipse GSX
    13.204 @ 103.722 · 2G DSM
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  15. MrBoxx

    MrBoxx Moderator

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    Yeah, you did. :thumb:

    Out of curiosity, is that a 2.5" or 3" gasket? Reason I ask is that I work at Checker Auto Parts and the largest gasket we have in stock, as well as in stock at the depot store, is a Fel-pro composite gasket that measured around 2.6" inside diameter. I tried finding a 3" gasket for the people who didn't get them included in their Megan Racing downpipes. My MR downpipe, as well as cat-back, were supplied with all the necessary composite gaskets, and they all have that steel ring in the center.

    Tomorrow, I'll try to find out a part number for that gasket using the vehicles you mentioned and see if it matches up to anything we have in stock.
     
  16. gsxtacy

    gsxtacy Proven Member

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    My gasket measured 2.5" roughly...I did not inside caliper it or anything..just used a tape measure..

    :shhh:
     

    705  0

    1998 Mitsubishi Eclipse GSX
    13.204 @ 103.722 · 2G DSM
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  17. Calan

    Calan DSM Wiseman

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    Ummm... I know this is a bit late and after the fact... but if you were burning through the composite layer, there was probably an intermittent fitment problem which was (is) letting hot air past the gasket and allowing the burn.

    If you didn't fix the fitment problem, your mondo gasket fix may be temporary.

    Just mentioning this because of my experiences with an MR DP on a stock O2 housing. Not sure if it applies to your situation or not, but then again I'm drinking at the moment ... ROFL
     

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  18. vaboys2ndgen

    vaboys2ndgen Proven Member

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    Keith Knows The Part Number By Heart Mrboxx Ask Him. Its A 3" Inner Diameter Gasket From A '75 Ford I Think.. I Cant Remember Either Off The Top Of My Head. But I Know Keith(tuners Wiseman) Knows The Pn.
     

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    manual · 1G DSM
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  19. RipperXX

    RipperXX Proven Member

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    Try sanding the surface completely flat. I recomend a piece of sand paper over glass.
     

    Street Build 3K  10  9

    1990 Eagle Talon TSi AWD
    13.476 @ 105.48 · 1G DSM
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  20. DoyoFCT

    DoyoFCT Proven Member

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    I always use the permatex copper spray on exhaust gaskets, and never have an issue.
     

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    1990 Eagle Talon TSi AWD
    · 1G DSM
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  21. ist dwa

    ist dwa Proven Member

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    Centerville, Ohio
    I found a great 4 layer metal gasket that has a crush o-ring surface and is reusable. The bolt spread is perfect no notching needed.

    2.5" ID - designed for a Hyundai Truck cat converter V6- 2.7 DOHC

    Fel-Pro # 61499
    DP gasket.jpg
     

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