Exhaust Flange Leak

[Kent124]

What does everyone use as a sealant/gasket between 3-bolt flanges in their exhaust systems?

[So Cal Mark]

shouldn't need any sealer there

[Kent124]

Are there some sort of gaskets that can be used? Unless both flange surfaces are completely flat wouldn't leaks occur?

Pretty sure that is what is going on with mine. Making a test pipe with flex exhaust pipe and two 3-bolt flanges off a scrapped catalytic converter.

[manoa matt]

Permatex ultra high temp RTV sensor safe gasket. Its copper in color.

[So Cal Mark]

if the surfaces aren't flat, gaskets or goop will burn out quickly. If your flanges have 4 bolts there are gaskets. If you have the late 6 bolt flange no gasket was ever made

[boogiedude]

I believe IAP sells a gasket for the three bolt pattern, also you could go to Napa or checkers and ask them for gasket materials. Don't know if it'll last in the heat

[digitech]

For the 3 bolt flanges, there are copper gaskets to be used - no sealant necessary.

[azruss]

may be worthwhile to use a flat file on the one face to get it true.

[manoa matt]

I had/have a copper gasket. It must be installed perfectly the first time as it compresses when installed. If not done right, then it will never seal. There are also 3 bolt gaskets constructed similar to a head gasket. Its a fiber gasket reinforced with a metal fire ring around the center hole, they work good.

[Kent124]

Matt, where did you find the fiber gaskets?

[So Cal Mark]

I assumed you were asking about the manifold flange, are you asking about the catalyst flange? Most exhaust gaskets will use a metal ring along with the fiber material to prevent burnout

[Kent124]

Yes, the 3-bolt catalyst flange. Making a test pipe using flanges off an old catalytic converter. Getting exhaust leaks at both ends where the cat flanges are.

[manoa matt]

Kent, I think I found it when disassembling the exhaust system on a parts car. I kept it and have used it over a few times with the RTV on both sides of the gasket. Call all the typical vendors and inquire about the construction of their 3 bolt cat flange gasket. Here are links to the majority of them: http://fiatspider.com/f08/viewtopic.php?f=5&t=12928

If no dice, assemble the system and insert a feeler gauge between the flanges to find the low and high spots, then mark the high spots. Disassemble and grind/sand down the high spots so the mating surfaces match, then apply a thin coat of the RTV, assemble and allow to dry for several hours before starting the car. Silicone is usually good to about 500-600 deg F.

[htchevyii]

Most exhaust shops have a variety of gaskets hanging on the wall for easy match up