vauxhall astra 1.8 auto dumping coolant

[ellisvernon1]

my grandfather bought a car from a local garage about 4 years ago , it keeps dumping all of its coolant , its had a 2nd hand engine about 2 years ago as the car overheated and seized , since then the car keeps dumping all of its coolant and overheating the garage has replaced a coolant pipe and the coolant cap on sepperate occasions but it has just dumped its coolant again , im wondering if anybody else has ever had this problem before and can you point me in the right direction