cache-control IIS8 always set to private

I tried changing the common headers to Expire webcontent immediately. Cache-control still shows up as a private in fiddler.

I tried setting a custom header of name:Cache-Control and value: no-cache at which point fiddler shows Cache-Control:private,no-cache

I've ruled out any code setting the header because i tried this on two sites on the same server, one of which is pretty much all static content with no code. Definitely no code touching any http headers. And it still wont let me set cache-control:no-cache

Any suggestions?