Clean Tailpipes: Cat Efficiency?

[CitroJim]

My Activa is the very first car I have ever owned to be fitted with a catalytic convertor. I notice it always runs a totally clean tailpipe. So clean in fact that the tailpipe is actually rusty up inside

I note that quite a few other cars run equally clean tailpipes and yet may others don't and are quite black and sooty. Next doors 02 plate Astra is squeaky clean although, by contrast, I know of another 53 plate Astra and an older R plate Omega 2.0 petrol that run exhausts that resemble old factory chimneys

Does this clean tailpipe effect show the cat is working really well whereas a black and sooty pipe shows it is not or is there some other reason?

My non-cat 205GTI runs a dark grey but otherwise clean tailpipe. Does running both vehicles on Shell V-Power have any bearing on this?

[Kowalski]

The black soot is unburnt fuel, on a petrol car it means that at some point the engine is running too rich. Unburnt fuel can kill a cat if it gets enough of it over a long enough period so a petrols with a cat has to be inherently clean otherwise the cat won't live very long.

Generally on a cat equipped car (especially a newer one), soot in the tailpipe is a sign that something hasn't been or isn't working properly, maybe its just a sign that the car does lots of short journeys from cold...

[AndersDK]

I have no idea on the V-power effect.

But I do know that my cat'ed (231Kkm/144Kmiles) BX19TRI is an oil swamp and a smoker. Not unheard of with this engine. Exhaust is sooty like a chimney, but it still passed its MOT 4 months ago. I know the cat is in danger because of the high oil consumption
My other cat'ed (167Kkm/104Kmiles) BX16RI is exactly to your description : rusty but otherwise fairly clean exhaust pipe. This engine is a non-drinker & non-smoker.
Both are '90 vintage and born with cats. Believe the cats are 'second generation' though.

Both cars are used for daily commuting. 19TRI is running 66km/41miles round trip daily. 16RI running 56km/35miles round trip daily.

Note that even new cars - or low milers - may have sooty exhaust by the fact they are doing too short daily round trips to make the cat work efficient.