03’ e53

Trying to solve coolant issue. Acquired a car with a cracked coolant reservoir, replaced it, cracked another.
Car has new waterpump and coolIng fan clutch, thermostat and radiator and operates in normal temp range. 10 min drive to operating temp causes the cooling hoses to be tight which I assume is normal. On shut off I hear a tiny air leak that appears to be radiator cap.

normal to build up that much pressure in 10 mins?

i will pressure test when it cools down to make sure it’s the cap.

FWIW- does not fail the block exhaust gas test.

Thanks