Why does my BMW 318ti over heat so quickly I have replaced the Thermostat water pump radiator and rebuild the cylinder head.?

my 97, 318ti did the same thing, replaced every thing, spent 3 weeks tring to solve problem.

new raditor but used my old cap. my old cap didnt hold the pressure needed.

bought new $15 cap.

so for now the raditor cap was the problem.

now i have to solve the problem with my drivers side window comming off track.