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Elderly cats - Richard Hall
The emissions figures for my 12 year old, 140,000 mile Audi were CO 0.09%, HC 78ppm. Minimum even for a post 1992 vehicle is 0.3% / 200 ppm, although my car gets tested on the older standards (3.5% / 1200ppm). So presumably the catalytic converter is working just fine. Judging by its external condition it has been on the vehicle for a very long time, and could even be the original. Do 'cats' usually deteriorate gradually, or fail suddenly without warning? At this rate, it seems that mine is more likely to rust through than fail internally.
Elderly cats - David W
Richard,

Despite the scare stories I haven't had to replace a cat yet because of MOT failure. And bear in mind many of my vehicles are from the mid-early days of cats and showing mileages up to 150K.

Just the one changed on Fiests XR2i 1800 where it broke up, rattled and blew most of the bits into the rear silencer.

What do you expect when the cat was the first thing to hit the ground as the "girlie" landed the thing after Fen yumps.

David
Re: Elderly cats - J Bonington Jagworth
I'd like to know how cats on 4WD's react to being immersed in water when hot. I know most 4WD owners don't go near big puddles, let alone streams, but presumably they should be able to...
Re: Elderly cats - Cliff Pope
Mine's done 255,000 miles, Volvo Torslanda, 1993. No problem at the last MOT.
I've been told, I think in an earlier thread, that CATs are stainless steel so don't rust, but either a) become poisoned because of a worn engine, or b) become physically damaged inside through impact or shock of being suddenly cooled in deep water.

I have also heard that there are ordinary ceramic-based CATs, which are vulnerable to sudden cooling, and tougher ones that can stand total immersion.