Exhaust manifold gasket keeps failing (4 times in 5 months)

[foogan]

I took my 02 P5 to the reputable local muffler shop to have the gasket replaced between the manifold and catalytic converter 4 months ago in November (I've owned the car since August). The replaced gasket has managed to re-fail approximately every month or so (I'd notice the relapse at about 3 weeks, finally take it in at 5 weeks) since then. I had it in twice since November, and it is now March and it has been noisy for a couple of weeks *yet again*.

-Why does this keep failing?
-The same mechanic at the shop did the work all three times. The third time he did it (2nd time RE-doing it), he was perplexed by it, and seemed determined to do everything right. Yet it still resurfaced a few weeks later.
-Upon the 3rd time, the mechanic said something like "I'm not sure why it keeps happening... Maybe the motor mounts? Dunno..."

He "threw" the idea out there that it could be the motor mounts destroying this gasket. I don't really know otherwise.

Has anyone else had this problem?

It cost me $30CDN originally to have it fixed. It's been free every time since. And like I said, this is the most reputable shop around these parts, but of course that doesn't necessarily mean the mechanic isn't slack or lazy, maybe he's not bothering t

 

[Dpwhitehead1]

yeah, motor mounts wont cause it to fail. ..

i'm thinking they're not using MAZDA specific gaskets and they're not as strong. also, there's an actual tightening sequence for them. and lastly, the exhaust studs/bolts could be stretched and thus not actually working.

 

[StealthWyvern]

clogged cat creating excessive back presure maybe? no idea really

 

[CR3 Motorsports]

Is he torquing the manifold down properly? I would check on what kind of gaskets they used to replace. Did he show you the gasket?

Also if he didn't torque it right, The manifold might be warped.

 

[foogan]

Sorry to abandon the thread for so long..

Update: I was mistaken, it's the gasket between the cat and downpipe, not the cat and manifold.

I took it back in Friday, they replaced it again, and also replaced the 3 bolts and 6 nuts as well. And rather than using a gasket sealer on the gasket, he just made sure the metal was bare, smooth, and clean for a tight, dry seal on the gasket. It's now Wednesday, and a few hundred miles later, and so far so good.

Also I'm not sure about a specific "tightening sequence". Since there's only 3 bolts, I'm assuming it's scientifically impossible to do them in the wrong sequence. (stoned)

 

[foogan]

Update: Still good!