Why did my exhaust gaskets live <34k miles?

[IamFODI]

Talking about the gaskets between the headers and the cat section. Replaced both at 95k miles and they started leaking again before 129k.

Any thoughts on why? If it's possibly my fault, I'd love to know so I can be more careful this time.

[Tbonem3]

Didn't see this was the e9x section nvm

[IamFODI]

What's the cat section? Cats are in the headers on these cars.

The primary cats are at the very front of the center section:


The gaskets in question are #3 in that pic.

The headers themselves are just tubes.

[Slideways]

As long as you installed them correctly, they should not fail after 35k. What indication is there that they are leaking? TIS says to replace those self-locking nuts and torque to 27NM.

[IamFODI]

As long as you installed them correctly, they should not fail after 35k.

My suspicions exactly.

What indication is there that they are leaking? TIS says to replace those self-locking nuts and torque to 27NM.

Car sounded louder than normal and sometimes ran a slightly rough. Got under it when it was cold, had someone start the engine, stuck my hands near the flanges, and felt a slight breeze around each flange.

When I first replaced these gaskets, I definitely replaced all the hardware and I’m pretty sure I torqued everything to spec. Maybe I did a worse job than I had thought.

[Slideways]

My suspicions exactly.


Car sounded louder than normal and sometimes ran a slightly rough. Got under it when it was cold, had someone start the engine, stuck my hands near the flanges, and felt a slight breeze around each flange.

When I first replaced these gaskets, I definitely replaced all the hardware and I’m pretty sure I torqued everything to spec. Maybe I did a worse job than I had thought.

It does not sound like it. Are both sides leaking and are these factory pipes?

[IamFODI]

It does not sound like it. Are both sides leaking and are these factory pipes?

Yes and yes.

[heinzboehmer]

I’m pretty sure I torqued everything to spec.

First thing I'd do is check the torque. Maybe you forgot to torque them or something.

Another possibility is that the gasket mating surfaces were not completely clean and caused a bad seal.

[tdott]

Have you removed the mid section since you installed the new gaskets? I usually consider them one time use.

Also I like to torque the right side first with the fixed flanged, that would pull the xpipe closer to the headers, then tighten the left side with the movable flange. I've had better luck since I started doing that.

[IamFODI]

Have you removed the mid section since you installed the new gaskets? I usually consider them one time use.

One-time-use is my understanding as well. I have no record or memory of pulling the cat section since installing the gaskets.

I did have to pull the muffler section for something fairly recently. Maybe we didn't quite support the cat section enough and ended up tweaking the flanges at the headers or something? That's all I got.

Also I like to torque the right side first with the fixed flanged, that would pull the xpipe closer to the headers, then tighten the left side with the movable flange. I've had better luck since I started doing that.

Nice. Thanks for the tip.

[bigjae46]

Always replace the hardware with those donut gaskets. At least replace the lock nuts. If you tighten the fasteners improperly, you'll get a hot spot on the gasket and it will blow out a section of the gasket. Then the gasket just comes apart.

[IamFODI]

Always replace the hardware with those donut gaskets. At least replace the lock nuts. If you tighten the fasteners improperly, you'll get a hot spot on the gasket and it will blow out a section of the gasket. Then the gasket just comes apart.

A-ha. There’s a plausible hypothesis.

I did use new fasteners and thought I had torqued them to spec, but I guess it’s worth a second look. Thanks for weighing in.

[IamFODI]

FWIW: turns out my engine mounts were shot and there were holes in the exhaust between the primary and secondary cats. We think the excess engine movement plus year-round-DD-in-the-northeast rust might have accelerated the failures, and I wrongly attributed (most of) the excess exhaust leaks to the donut gaskets.