As covered in earlier threads the catalyst basically only accumulates the soot unit it gets hot enough to burn off. If you do short hop city driving only it's going to get pretty clogged up. Also if it gets loaded with soot and then starts to burn it off the cat can get too hot and melt the substrate. The bottom line is if you have a trap/cat you want to be sure you get out on the highway at speed at least once a week or so (in fact that's not a bad thing for the rest of the engine too). I've had a completely stock trap exhaust system for the last 15 years and never had a problem but I drive in a warm climate and 70/30 city/highway. If I lived in a cold climate with mostly city driving I think I'd consider removing the trap altogether. Given the fact that these cars were really only sold in areas with a relatively warm climate and lots of highways (or freeways as they call them in LA) they were probably not designed to make it through a cold winter of nothing but city driving.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold