How often will a CAT need replacing?

In theory, a CAT should last the lifetime of a vehicle. However, due to the extreme thermal and mechanical stresses it is exposed to, it is anticipated that a CAT will need replacing at least once during the lifetime of a car. In practice, CATs on some car models are failing far quicker. This is mainly due to ceramic monoliths breaking up and fracturing in the casing.

Will a catalyst work on short journeys?

CATs have to reach a light-off temperature before they work properly. This can take up to 3 minutes in winter periods. It is for this reason that CATs are placed as close as possible to theexhaust manifold so that they warm up quickly.

Why do CAT emissions sometimes smell of rotten eggs?

This can sometimes happen when trace elements of sulphur in petrol form minute quantities of hydrogen sulphide on the catalyst. This generally only occurs when there is a rapid change of engine speed and load. It is a phenomena of new units and should reduce with age.

What servicing will a CAT require?

CATs are service free items during their lifetime on the car. It is the other elements of the emission control system that may cause damage to the CAT and ultimately lead to its replacement. Motorists should always have their cars serviced at the correct intervals.

Will a CAT affect my car’s performance?

No, since today’s lead-free petrol-engine vehicles are designed to run specifically with CATs fitted.

Does a diesel engine need to be fitted with a CAT?

Some diesel cars are already fitted with catalytic converters, but 1997 legislation will require the majority of diesel cars to have converters.

Can I use fuel or oil additives in my CAT equipped vehicle?

Unless the additive manufacturer clearly states that the product is CAT compatible it is advisable not to.

How do I tell if the car has a CAT?

CATs were progressively introduced onto cars around August 1992 but many were registered in
1993 without CATs. (Remember CATs fitted to vehicles before 1 August 1992 are not subject to the MoT CAT emissions test.) The CAT will be the first box in the exhaust system. CATs are normally distinctive, but can sometimes be confused with small silencers. The presence of a Lambda sensor will mean that the car has a CAT. If in doubt, refer to the VIN number or engine number and check in the handbook. If this is not possible, ask the car manufacturer’s main agent.

Can catalysts set fire to grass?

Since the exhaust systems of all cars run at very high temperatures it is advisable not to park your car, whether fitted with a CAT or not, in long grass. Front end temperatures can rise to as much as 900° C. Due to these high temperatures the majority of CAT assemblies incorporate heatshields.