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HOW TO: Replace Exhaust Studs at SCR

16080 Views 4 Replies 5 Participants Last post by  hbilow
Since there are a few documented cases of these bolts shearing off and other cases where dealers are replacing them voluntarily, I decided to change mine out since I am outside my warranty and I had significant laminar corrosion all over the flange. I also have a persistant P11D7 code (may or not be related, guess I'll find out). If you are going to tackle this yourself, I recommend doing it sooner than later while it's still easy to remove the studs. If you can change oil, you can do this repair easily.

Tools needed:
13mm wrench or deep socket
MAPP or propane gas torch
Wire brush/Emery cloth
Safety glasses

Parts needed:
(1) Gasket (2 bolt holes) P/N 13229872 $6 from my local dealer
(2) 1-1/2" long x 5/16" stainless steel bolts
(2) 5/16" stainless flange nuts or regular nut with flat washer
I think OEM is metric (did not check), but imperial was cheaper. Otherwise it would be M8 x 40mm

(2) 5/16" stainless lock washers
(2) 5/16" stainless flat washers
Orange exhaust silicone

1) Jack the front half of the car up and place on jack stands or use a set of ramps. Or if you're lucky, throw it on a lift.

2) Unbolt the two flange nuts from the exhaust just behind the SCR (big muffler looking drum about midway under the car) and disconnect the pipes. Slide the rear exhaust pipe toward the back of the car and to the driver side being conscious of the two downstream sensor wires (should get about 3" gap to work with). Remove old gasket.

3) With MAPP torch, heat the stud/flange until the stud glows red hot, will take a minute or two. You can use propane but it will take a bit longer. Try not to cook the underside of the car and point the flame parallel to the ground. Firmly hit the stud with the hammer, it shouldn't take too much to get it out. Be careful when the stud comes out it doesn't hit you in the face or fall on something flammable as it will be stupid hot. Same process for the other side.

4) When the flange cools off, clean the inside mating surfaces. I took a damp cloth and cleaned the sanding debris from inside the pipes before connecting. I also applied a thin bit of high temperature silicone to both sides of the gasket (more on that later). Insert bolts and sandwich the gasket in.

5) Crack open a cold one and clean up, you are finished.

As noted, the flange had a ton of rust/corrosion, significantly more than you would expect for a 2 year old car. After I took it apart I noticed liquid seeping through which could be DEF fluid and/or water from the combustion process. A member mentioned DEF could be causing this odd corrosion and I think it's possible based on the fluid and lack of corrosion at the flange connection below the dpf. The gasket itself also had rust, so I imagine the seal wasn't the best either which is why I added some silicone (hopefully the silicone won't have adverse effects on the downstream sensors.. use it at your own risk).


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Well done young man.

Thread stickied.
Excellent and super useful writeup, thank you!!
40k on ours, hoping the studs won't be too difficult if I just PB blast the living **** out of them overnight.

Wondering how hot this part of the exhaust gets. If it's not all that high-temp, POR-15 might be a great anti-rust solution for the flange.

Or if the two flanged parts are relatively removable, have them ceramic-coated inside and out, to ensure it does not corrode from the inside.
I recently discovered I had one of these studs broken. Rather than replace with 5/16", I used bigger 3/8" bolts. One side went in as-is, the other side downstream flange had to be opened slightly with a carbide drill (The flange is hard, and will ruin a common drill bit). Also opened gasket bolt holes slightly with a Dremel.
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