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Gasket sealer on turbo to cat connection?

1045 Views 6 Replies 5 Participants Last post by  northcountryguy1
My "OEM Grade" MagnaFlow cat broke at one of the welds (cat/pipe joint nearest turbo) after 5 years so I'm replacing it. (BTW, my original cat lasted ~11 years so you be the judge.) Just got the old unit out. Last shop apparently used some copper based gasket sealer on the turbo to cat flange joint. Do I need to use this on the new gasket?

Also, the flange on the downpipe appears to have some remnants of the prior gasket literally welded to the face, see the image below. (Turbo flange is perfectly clean/smooth.) I tried to scrape it off but no success. Is this going to be a problem for making a good seal? Or use the sealent here, too?

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take something flat, piece of steel or file...and 80 -120 sandpaper and randomly sand it , each time you pass over it you will incur a low spot (minute) but over time these low and high spots will "cancel" each other out and give you a pretty good flat surface, as to using exhaust sealer (brownish tan stuff) don't think it would hurt at that connection aft and not pre cat. ,however properly and sequentially torqued gasket will do it's job, that is why there are only three bolts rather than a greater number.
Gasket sealer is up to you. Copper RTV is a trick a lot of racers use for headers that keep blowing out gaskets. Seals better than about anything actually
I'd seen you shouldn't use silicon based sealant prior to the cat since it can foul it permanently so I was surprised to see it used there. I'd prefer to just use the gasket and didn't think a sealer should be necessary. I'll clean up the flange on the downpipe. This will be the last cat I put in this thing so just has to last a year or two at this point.
the other thing is get a good re-enforced gasket with the metal material "rolled over" on inside I.D. of it, no migration of gases eating a path
I've R&R'd my cat/downpipe twice over the last year. Just used new gaskets and all is leak free. My recommendation is not to use anything additional. Just get that surface clean/smoother with some emory cloth or something.
I understand that RTV sealer can damage the O2 sensors, and manufacturers recommend not using it to install their sensors.
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