Why is my tubing gradually turning into oval shaped?

[RMSwins]

trance, the collapsing of the tubing is a common problem with stronger pumps. If you read the Iwaki manuals you will see that they specifically say you should make sure to avoid this at all costs.

No.... sorry, but just plain no. These watercooling systems are all zero pressure environments, hence the reason why you can bleed the system without having to seal the reservoir. Trance565 is right. The tubing may be collapsing due to a localized blockage. A normal hose without blockage on a strong pump would not collapse due to the uniform suction on the walls of the tubing. The inward force on the tubing walls counteracts each other and prevents collapsing. Blockages usually create microscopic low pressure zones against specific parts of the tubing walls. (edit) This is all assuming you are using the same ID tubing as the stock barbs on the pump and that you are not using extremely thin walled tubing.