When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Unscrew your cap and see what happens. It sounds like the cap isn't letting air in when the system cools and that would reflect in a collapsed hose.
X2 on the cap, especially if it is aftermarket. I had this problem and ended up getting a Ford cap and new bottle from Clay. The old bottle from Dorman would not seal properly with several different caps tried.