wyovino

I bought a set of used mufflers years ago and sent them to Fister for modification. They have been great and I still have my original ones that had about 37k miles on them stored in my garage. One of my modified mufflers started sounding much louder today and when I looked at it it seems to be corroded at the seam (nothing to do with Fister). When I start the car it sounds very loud but after a few miles it goes back to normal.

1. Is there a physical reason why it would go back to normal after a while - like expansion?
2. Can the seam be repaired/welded or should I replace the one muffler? The price of the Fister mod as gone up and shipping it across country isn't cheap.

zbomb

1. What does heat do to metal? The expansion (or contraction) of any material is due to the kinetic energy of its atoms. When a material is heated, the increase in energy causes the atoms and molecules to move more and to take up more space— that is, to expand. This is true of even a solid such as a metal.

2. A muffler shop can likely repair.

168Sierra

You can repair the seams by welding. Fister did that to a pair of my mufflers when doing their mod several years ago.

996C438

Any competent welder will be able to weld up the seams that are split or rusted . Hopefully the insides are in better shape than the outside .

wyovino

I'm aware of that but have not witnessed a muffler "fix itself" from a hole before. The difference is dramatic, especially given that it only takes a couple of miles. Something new every day.

pdxmotorhead

I've had severs unrelated exhaust systems over the years that did the same thing, loose clamp, tightens when it gets hot, cracked weld , loose manifold bolts same..
As noted prior in thread its a function of thermal expansion.

If it were me and since I've had my system off a couple times I'd pull the mufflers, and use a stripper wheel on them to get them clean if I didn't find any other issues and use a shop vac to pressurize the muffler and spray down with soapy water the cracks will bubble... The long seams if cleaned, can be welded or brazed if the seam fold is starting to give up.. POR has a exhaust paint that has worked well for me thats a nice silver..

wyovino

Update. It wasn't the muffler. It was the connection between the exhaust manifold and catalytic converter. The bolts had rotted out. All good now.

168Sierra

Nicest kind of problem to have, easy and cheap to fix.

Mike Murphy

Explains why it got quieter when hot. Metal expansion of a long tube will make it noticeably longer than a short tube expanding due to the same heat.