Mostly as above though the old idea of 'sold as seen,' is no longer valid. Sale of goods regulations apply and you can not avoid legal responsibility in the eyes of the law. If the engine fault could reasonably have been either known or foreseen, or was in actual fact known at the time of sale then your friend would have some liability. If that was true then proving that would be difficult in any case. If the car is less than around 6 years old and the fault was either a known design fault or weakness then there would be some comeback against the manufacturer irrespective of warranty periods.
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