Cool photos!

In answer to the original question, most of the time the vent on the radiator cap is bad causing the hose to collapse because there is supposed to be a check valve vent that allows atmospheric pressure in when needed.

You didn't mention the brand/type of cap you bought, but make sure you get the right one, from the dealer if necessary, they are relatively cheap.

Try another brand new good quality cap and see if that does the trick. You may have just gotten a bad one, that has been known to happen.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz