The Toyota rad pressure cap opens at 0.9 Bar = 13.0534 Psi. You probably have a cap set to a very high pressure which resulted in ballooning of the rad tubes. Surely this is the first time I have seen something like this.
My experience with transverse (side ways) tubing Rad has never been so good. When you look at the rad from front you will notice that the cap is lower than the tubes, meaning that the top 7 - 8 rows can never be filled with water, an ideal place for steam to be accumulated, steam is far hotter than the water it'self and the pressure in those tubes must be way higher acting on the water which is blocking the rad cap.
Electric fans that are almost touching the rad core would only pass air in a round band leaving the center, and sides without air, in short a very small area is actually transferring the heat from the core, This is why a suction shroud with suitable distance between the fan and the core ensures even flow through the entire rad surface with better results.
