Dave Plowman wrote:

In article ,
Nick Maclaren wrote:

Worse, they work only after
the engine has warmed up (about 5 miles) and the average trip in the
UK is about 3 miles.


This may have been true when they were first introduced, but modern types
work much more quickly. FWIW, a cat doesn't rely on the engine
temperature, but that of the exhaust gasses which are largely independent
of this.



Cat still takes a mile or two to get hot tho.
Engine may take longer.

During that time the engine will be running very rich, and the cat will
allow huge amounts of unburnt fuel to spew out.

When I reverse the car out first thing, the exhaust STINKS of benzene
and other aromatics.