1988 BMW 323

I in replaced the engine in April the engine gaUAGEs still go read hot an go up to the red. I took it back and the mechanic said I needed a cluch fan so I brought one while my dad was begin to take it of he found that the bolts were lose to the c-fan he tight them still run-hot. My dad replaced the thermostat, the sensor on the engine replaced that fan switch, replaced all the fuses. It still running hot it take about five mins to rise. My question is what would make this car run hot after all been done. Also when an engine has been replaced with another used engine what should the mehanic replaced on that used engine before returning it to the customer.