How to Replace an Exhaust Flange Gasket

by Jody L. Campbell
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exhaust pipe image by A74.FR Ben Fontaine from

All vehicles have at least one pipe with a flange connection. The front pipe or header pipe bolted to the manifold uses a flange of some type. Many modern vehicles now connect other components, such as catalytic converters, downstream exhaust pipes and even mufflers, with flange connections. With the car on a lift and a mechanic that knows what he is doing, the repair could take a mere few minutes. With a home repair mechanic laying on his back with limited tools, the repair could become complicated.

Step 1

Inspect the pipe with the leaking flange gasket carefully before attempting to disconnect it. Front-pipe-to-manifold flanges often require the rear flange to the converter or pipe be separated in order to access the leaking gasket. Sometimes unhooking an exhaust hanger somewhere down the exhaust stream might allow enough flexibility to forgo the rear flange disconnection.

Step 2

Determine how the flange is connected. All front-pipe-to-manifold flanges are secured by nuts to the studs of the manifold. Downstream flange connections may use studs on one side and nuts on the other or simple nuts and bolts. Downstream studs can be distinguished by round heads which, unlike a hex bolt head, cannot be held with a wrench. Studs have grooved notches in their shafts and do not require a box-end wrench for removing the nut. Nut and bolt connections will require the bolt of the head be held stationary (with the wrench) while a ratchet and socket loosen the nut (or another wrench).

Step 3

Disconnect the flange hardware. If necessary, heat the nuts of the connection with an oxyacetylene torch. Using a portable propane torch may not heat the nut up enough or could take a considerable amount of time. Heat just the edges of the nut and not the bolt. This will expand the nut. Once the nut is cherry red, turn off the torch and remove the nut. For front pipes, a ratchet, long extension and socket are most likely required.

Step 4

Repeat for each nut and stud/bolt connection of the flange until all retaining hardware is removed. The studs will remain intact on their respective exhaust components.

Step 5

Separate the flange connection. This is where the exhaust pipe hanger tool may come in handy. Releasing one or more exhaust hangers near the flange connection may give the exhaust system enough flexibility to access the mating surfaces of each mating flange. As mentioned earlier, it may also require separating the other connection of the exhaust component with the compromised flange gasket.

Step 6

Clean each flange connection's mating surface with emery cloth or medium-grit sandpaper, after allowing the exhaust system to cool down, if a torch was used.

Step 7

Apply a level amount of high-temp Perma-Tex (O2 sensor-safe) compound on both sides of the gasket. Place the gasket between the flanges. On most flange connections, there's a small piece of pipe protruding on the inside of the flange to place the gasket on, depending on the type of application. Some front pipe gaskets are called "donut" gaskets and fit into a ball-flared exhaust pipe.

Step 8

Reconnect the flange connection, after replacing the system on hangers, if applicable, with new hardware (nuts, bolts, washers and lock washers).

Step 9

Start the vehicle and check the flange connection for leaks. If necessary, re-tighten the hardware.

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