All petrol engined cars sold in the UK since 1993 are fitted with catalytic converters - "cats" - yet many owners don't clearly understand what the "cat" does and what you shouldn't do with it.

Put simply, the "cat" is a high tech exhaust gas ''scrubber'' which filters out most of the toxic gases produced in an internal combustion engine. While cats are proven and safe there a few simple rules which should be followed to ensure their safe use in emergency situations.

ONLY use unleaded petrol in a cat, leaded petrol will soon clog and destroy the cat. If you accidentally use leaded fuel in a cat equipped car and realise your error you have no choice but to drain out the leaded fuel and re-fill with unleaded.

NEVER push or tow start a cat equipped car, as this can flood the cat with petrol which could ignite. NEVER press the accelerator pedal before switching off the ignition. While this was commonly done with older cars fitted with mechanical fuel pumps, if you do this with a cat it loads it with fuel which can subsequently ignite.

AVOID parking a cat equipped car on long grass or leaves, such as when visiting a Summer outdoor event, they reach very high operating temperatures and could ignite first grass, then car, then the rest of the car park. Allow the car to cool before parking it.

When checking your prospective car's exhaust pay particular attention to the cat's physical condition. The cat is usually located about halfway along the exhaust system under the car and it can be damaged by excessive speed over road humps or running over debris.

If it shows signs of damage being bashed or flattened in any way it may no longer be operating correctly. If so check the exhaust gases at idle and if they look dirty have doubts about it's efficiency, it could well fail it's next MOT where cat testing is rigorous and may cost up to £1, 000 to replace.    

Article © Graham Benge 2007

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