Remove exhaust donut gasket residue?

[Percival P. Cassidy]

I'm trying to replace the donut gasket on our 2008 Pontiac Vibe
(rebadged Toyota Matrix) -- the donut at the connection between the pipe
connected to the resonator and the pipe connected to the muffler.

I've scraped and chipped away a lot of black and grey stuff, but there
are still lumps in places, and in other places something with a regular
cross-hatched appearance that looks as though it might have been the
outermost layer of the original donut.

Do I have to get down to bare shiny metal? If so, is there an an
alternative to just chipping away and wire-brushing or using a
small-enough drum sander?


The muffler and pipe are off the vehicle, so I could even use a propane
torch if it would help.

Perce

[Motors Advisor]

Here is a list of tools and materials that may be needed to replace the exhaust donut gasket on your 2008 Pontiac Vibe:

Tools:

Set of wrenches (such as a Craftsman Evolve Adjustable Wrench)
Set of sockets (such as a Craftsman Evolve 3/8-inch Drive Socket Set)
Exhaust hanger pliers (such as a Lisle 54600 Exhaust Hanger Plier)
Wire brush (such as a Weiler Vortec Pro Knot Wire Wheel)
Safety glasses
Gloves
Rags or shop towels
Optional: Power drill with wire wheel attachment, such as the DeWalt DW4910 3-Inch by 5/8-Inch-11 Knotted Cup Brush
Materials:

Exhaust donut gasket (such as Bosal Exhaust Gasket)
High-temperature RTV silicone (such as Permatex 81160 High-Temperature RTV Silicone Gasket Maker)
Optional: rust remover or degreaser (such as POR-15 45904 Marine Clean)
Please note that the brand and model numbers I've provided are examples and may not be available in your area. There may be different brands or models that work equally well, so feel free to shop around for the best options for you.

Also, make sure you consult your vehicle manual before starting the repair and make sure to follow the recommended torque specifications when tightening the bolts

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For full context, visit https://www.motorsforum.com/pontiac/remove-exhaust-donut-gasket-residue-22707-.htm

[Motors Advisor]

When replacing the exhaust donut gasket, it's important to make sure the surfaces that the gasket will be sitting on are clean and smooth. The residue you're describing could potentially cause issues with proper sealing and could lead to exhaust leaks.

To remove the remaining residue, I would suggest using a wire brush to scrub away as much of it as possible. If that doesn't work, you can try using a chemical rust remover or a degreaser to soften and break down the residue. Be sure to wear gloves and eye protection when using these chemicals.

If you have access to a power tool such as a die grinder, you can use that with a wire wheel or sanding disc to remove the remaining residue. If not, you can use a hand-held wire brush or sandpaper.

It's not necessary to get down to bare shiny metal, but the surfaces should be clean and free of any large bumps or rough spots. Once you've removed as much residue as possible, wipe the surfaces down with a clean rag and make sure they're dry before installing the new donut gasket.

As for using a propane torch, I would advise against it. The heat from the torch can warp the metal and make it difficult for the gasket to seal properly. It can also cause the metal to become brittle and more prone to cracking.

If you have any difficulties with the repair, you can always consult a professional mechanic. They will be able to diagnose the issues and suggest the best way to fix it