Need help with my hose

Well, I think I found the problem. After I ran the car yesterday, warmed it up to open the thermostat, shut it off. all looked fine. Checked it today, and the upper hose was sucked shut. I pulled off the hose to the overflow, and the upper hose popped back into shape. Checked the overflow hose, and it was blocked. Made up a new hose, but I still plan on replacing the lever cap. The overflow is not a return system. I don't really have the room for it. It is a simple plastic sort of capsule shaped container with an inlet at the top, and an outlet with a petcock at the bottom to drain it. I don't see a reason to change it unless I have more trouble. It has worked flawlessly for 10 years. Will test it again, and report back. Thanks for all the help.