M54 3.0i Exhaust Gasket Replacement at Catalytic Converter
 

Hey everyone, looking for some tips here. Our 2005 3.0i began leaking from a blown out exhaust gasket where the catalytic converters bolt to the center muffler (diagram attached). This seems like an odd spot for an exhaust leak, and is the first exhaust leak I've experienced on a modern BMW in over 10 years.

The removal of the four nuts looks treacherous, so I'm bringing this one to a local shop so they can use a torch if (when) needed. I'll be providing the shop:

Two new gaskets, BMW part number: 18107502346 (number 3 in the diagram)
Four copper nuts, BMW part number: 18301737774 (number 2 in the diagram)

Gasket being replaced is #3 in the attached diagram image.

My question is, how often do the studs strip out during this job? Is it possible this turns into a difficult job where the studs need to be drilled out from the cat pipes and replaced with bolts?

Thanks!

They will likely strip or have to be cur out so new ones are not unusual replacement.
But if you're taking it to the muffler shop, this is standard stuff that they're ready for and do it daily so why worry?

You should be fine. I have done a head gasket on an '05 X5 3.0 and removed the exhaust nuts you are referring to...my X5 w/ 125k miles has spent its entire life on the salty roads of NH & MA..

Unlike other BMW series (E39 & E46) the E53 X5 uses nuts AND BOLTS at the downpipe connection. The E39 and E46 uses pressed-in studs that rot away, and if they snap (likely) they have to be pounded or drilled out, which is very difficult when underneath the car.

Its a little awkward getting a wrench on both the nut and bolt at the downpipe connection on the E53 but not that difficult. If they do snap, they simply pop out with a tap.

It's unlikely that all four will snap, but if you want to be thorough, add 4 new M10 x40mm exhaust bolts, part #11621427586. They are a little pricey

I had no problems with those parts on my 2001 3.0i with 186k miles at the time when I did the engine work. I actually reused nuts and bolts (and I'm not even sure if I replaced the gaskets) with no problems. California car, so that does make this a little less surprising and maybe relevant.

The fact that you had a failure in the first place suggests you might not find things easy to work on in there.

Had to replace the same gasket on clients e92. He broke a bolt when he hit a big pothole.

I had to get new gasket but I replaced both bolts with some m8 10.9 bolts. Nuts were "fun" to hold on the back side I think I cut some flange out of my way.

Thanks for all of the replies. This is exactly what I was looking for. I didn't realize it had bolts, I assumed studs like the rest of the M54's came with! Cool.

The bolts are on the catalytic converter diagram under engine, but don't show on the exhaust diagram for some reason. You're right, a set of four bolts is $67... yikes. Hopefully the originals don't snap or strip lol.

As to the comment for "why worry"... well you can't always trust a shop to take things to the finish line. My contingency plan is to have nuts, bolts, gaskets ready so they don't have to be ordered and have the car tied up for 2-3 days at some shop. Sometimes hand holding is required haha.

Good thinking.
What do you do for a living by the way are you a project manager?

Means and Methods are usually left up to the contractor. I was a PM for 15 years and I would never tell a contractor how to perform a task. I will just call them out if they fail to follow the contract documents.

I am not a PM. I have a few select places I bring my cars, 90% of work is DIY but some things I have to bring to the following places:

1. The Dealer $$$
2. The Skilled BMW Indie $$$
3. The Local General Repair Shop $

My exhaust gasket is going to number 3, where they will charge one hour labor for this repair. The Indie place will happily charge 3 hours for this simple job.

Now that I know there are bolts present, not studs, I may even attempt it myself this weekend after all. Sprayed it up with PB blast to help get it started!

Easy to do with a good 1/2 inch drive battery impact gun and sockets. On the tougher-to-access bolt heads, use a range of longer handles open end wrenches to hold. The long-handled offset metric box wrenches at harbor freight are a big help in this job.

3/8 impact gun probably wouldn't get it done.