Used car 2002 nissan Sentra (red)?

my little brother bought a car nissan sentra 2002 the car was 7,000. he put 3,000 and finance the rest. he bigot the car 6months ago. the car is giving him problems since he bought it every week he have to a bottle of oil, it cuts off he has taken the car back to the dealer several TIMES. the car smells to me like some type of water damage.he has to keep new car sent in it.he's 20yrs old at the time of the purchases is 19 just got licensees to fast a