Cat and O2 sensor Q

[jkarlsso@metabolex.com (Jonas K.)]

On 5/5/02 7:58 AM, "Dan Kraus" <dirtbike@warwick.net> wrote:

> Hey everyone,
> I'll be putting in a "new" Cat in my 16v this week and I wanted to know if I
> had to install a new O2 sensor? I heard that a used O2 sensor will harm a
> new cat.. Is this true?

Not exactly true, but somewhat.

Catalytic converters have a long lifetime. Most premature failures are due
to overheating, and when an oxygen sensor goes bad, it can cause an overly
rich mixture. Excess fuel in the exhaust will undergo catalysis in the cat,
and this generates a tremendous ammount of heat. The average car owner won't
notice the bad O2 sensor, but will notice the clogged/failed/melted cat.

As such, replacing the cat, without replacing the faulty O2 sensor would
lead to shortened cat life.

The proper remidy is to check the O2 sensor, _if_ it is faulty replace it.

OTOH, O2 sensors should be replaced every 60k miles or so. Waiting for
failure is not always the best approach. If a mechanic is installing the
cat, then it's only an extra minute to intstall the sensor, good for another
60k. Would take longer to check the old sensor.

So, to recap;

A good idea, but not a _must_, so long as the old O2 sensor is functioning
properly. 

HTH, 
Jonas