Marie Travers was surprised to hear the engine purring in her broken-down car - until she lifted the bonnet and found a cat.
Not only was the brown and ginger animal curled up in a tight spot near the battery but it was so skinny it looked like it had been there for days.
Mrs Travers, of Findon, near Worthing, had been trying to fetch her 11-year-old daughter Samantha from school when her Nissan Sunny conked out.
She called her father, Gerry Stedman, hoping would be able to start the car.
He promptly arrived and opened the bonnet to find the cat in the engine.
Mrs Travers believes the cat could have climbed in during a trip to Brighton on Tuesday because it was not one she recognised from the neighbourhood.
It was not noticed until Thursday.
She said: "When my dad opened the bonnet I saw the cat. I thought it was dead. I couldn't believe it was alive."
Mrs Travers, who has two four-year-old cats of her own called Branston and Pickle, plucked the cat from its hideaway and it purred in her arms.
She said: "It was in a very, very tight space. It couldn't move so when the bonnet was opened it just stayed where it was because it probably thought it still couldn't move."
Mrs Travers fed the small cat, which was ravenous.
She fears it could have taken shelter in the engine while she was taking her 18-month-old son Kieran to the Royal Alexandra Children's Hospital in Brighton for an appointment.
The only other time the car was driven was locally, to her daughter's school in Worthing, then to Broadwater to pick up her father to go shopping.
The cat was collected by the Worthing and District Animal Rescue Service, which took the cat to a vet.
Anyone who may have any information on its owners should call 07771 631949.
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