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What can I expect the life expectancy, by time and mileage, to be for the 2004 DTS mufflers?

Well, I’d say anything from maybe 5K miles to - oh, say 500K miles. There’s no way to put a number on it without knowing a lot more about the way the car is kept and driven. A lot of short trips, for example, shortens the life of just about everything including the muffler. A desert climate and a coastal climate are worlds different, as are northern & southern regions… You can’t, for example, compare anything about a car driven a couple miles at a time in the state of Maine, with a car driven 20 miles or more at a time in Arizona.

Depends on where you live and how you drive.

Lots of short trips don’t let the water condensation in the exhaust dry out. This can allow the muffler to corrode from the inside out.

If you live in climate where there is salt and deicer on the road, corrosion can happen as well.

If you drive with the throttle wide open all the time, that can wear the packing in the mufflers as well.

If you live in climate where there is salt and deicer on the road, corrosion can happen as well.

I’ve NEVER seen a muffler corrode because of road salt. They all corrode from the inside-out…Not from the outside-in. In order for Salt to have any effect…it needs WATER to pool…And that’s very difficult to do on a muffler who’s temperatures exceed 200 degrees.

The OP has omitted very vital details, including the current odometer mileage of the car, its geographic location, and the type of driving to which the car is subjected.

If this car is used for mostly short-trip driving, then I would say that the OP is lucky to have gotten ~7 years out of the mufflers. On the other hand, if it is used for mostly longer-duration highway use, then it is very premature for the mufflers to have rotted out already.

Even though I do not do as much highway driving as I used to, I have not had to replace a muffler on any of my recent cars, and that includes cars as old as 12 years with 170k miles on the odometer.

The only car on which I ever had to replace a muffler was my '74 Volvo. But, when you consider that virtually every part of that car was due for repair or replacement by 6 years/70k miles, the muffler was the least of my worries.

The reason I’m asking is that I noticed some black drip spots the size of a softball on the garage floor, in Birmingham, AL, under the front end of the mufflers this past week. The car has over 116,000 miles now; but, runs and sounds fine still. The black spots got my attention though. Don’t know what caused them as it’d been about 2-3 days since a run through a car wash, and had been driven dry a couple of hundred miles on an 85 degree day.

From that you can surmise the car has been mostly on long trips.

I have.

Mufflers have weep holes to allow condensation to drip out. After several short trips in cool damp weather condensation will wash black carbon out of the muffler.

I’ve seen mufflers rust on the outside, both in cold weather and in warm weather climates near the beach.

Today, most cars have stainless steel exhaust systems that last the life of the car. A back-fire can peel any muffler open however…

Have you had a muffler failure?

No muffler failure(s). They did both weep; but, sound fine. Life of the car is open-ended too. I bought the car new in 2004, and am familiar with its history of maintenance. Have kept it up with services and tune-up and replaced failed steering column donut. Did major tune at 100k. Recently ran through a treatment of fuel injector cleaner; but, that was a couple of tank-fulls ago. It may have contributed to the mufflers finally weeping though.

Most mufflers have drain holes so condensation can exit…

I guess you take a REAL SHORT trip on salted roads…

I remember reading about the exhaust system on a delivery car lasting 30 years because it was used day and night and almost never cooled off.

Well, they don’t actually use salt on the roads. It’s magnesium chloride or something, and some kind of liquid de-icer, or maybe it’s the same stuff in different form. Anyway, it’s not just salt, but it does seem to be corrosive.

I also regularly see mufflers where the outer shell is peeling away, kind of like an onion.

It’s the chloride part of salt that’s corrosive to metal, not the sodium, so yes, MgCl2 would be corrosive.

Also, they do use salt around here.

If you do a lot of short hop driving, expect another 5-10 years out of those mufflers. If you do a lot of highway driving, they should last another 10-15 years or more. Factory installed stainless steel mufflers usually last about 10-15 years on average.

It doesn’t have to be real short. The car will drip for hours after you drive it through slush, especially if the slush froze and then slowly melts off. Plenty of time for the muffler to cool down. Then even with the muffler being hot, that just evaporates the water and leaves a good portion of the salt behind, so the next time the muffler gets moist it starts to rust. Plus unless it’s very cold there’s salt and moisture in the air itself when the roads are salted, and so the muffler can rust just sitting outside.

My van is a’96 and has never needed a new muffler YET! I live in Misouri in a city that has snow, ice, cold, heat, and ice melting liquid.

The muffler started leaking on my 2000 Blazer back in January at 114k miles. The leak developed at the weld where the muffler is bolted to the main pipe. Evidently the weld is prone to corrosion because the rest of the stainless steel exhaust was in great shape. On the other hand, my 1993 Caprice still has the original stainless steel exhaust.