I have 540i/6 (swapped from automatic, brand new motor) two new radiators in the row pop around the neck area after 1~ hour of 'hard' driving. (near red line pulls, etc).

There is no overheating when driving 'spiritually'/daily nor is there any overheating when pushing it but every time I push it to extended period of time radiator pops.

Fan clutch,water,thermostat are brand new.

Any ideas guys? I don't think it should fail even when driven hard.

P.S 50/50 BMW coolant mix with distilled water + 4 shots of red line water wetter.