My 2004 XC70 has a hole in the side of the muffler. The escaping heat has actually blasted/melted a hole in the left-rear wheel well plastic shield! I crawled under to look at it and was dismayed to see that the muffler and converter are apparently all one unit. Is this true? Am I missing something? Why would anyone design it like that?!

 

Yep, it's a common setup on many modern cars where the muffler and catalytic converter are integrated into one unit. It's often done to save space and make the exhaust system more efficient.

 

I've replaced a rear muffler on a few cars and they came as one piece from that cat back so no surprise if you find the rear muffler assembly one tall unit.. With that said, you also have the option of having a muffler shop cut and weld in a new component without replacing the entire pipe. What you can do is check a Volvo dealer parts store to get a diagram of the components and the OEM part numbers to get an idea of what needs to be replaces. Check out https://www.tascaparts.com/v-2004-vo...ust-components and you'll see the 2004 XC70s have a downpipe/converter as a unit, a center muffler/resonator built into the long pipe then a rear muffler. Note on some models, there is a flex pipe between the downpipe and cat that can leak so its costly part to fix a $30 flex pipe (unless you weld in your own). If you have a leaky exhaust behind the cat then its either going to be the long pipe or the rear muffler.