Overflow isnt the Header tank I'm talking about
No header Tank then yes you'll need Radiator cap style rad (pictures might help of your engine bay)
but yes Auto is important part of the thing as there's a trans cooling loop built into the Radiator
Usually Turbo cars have a header tank, no turbos dont?
the Header Tank it bottom Centre in that image above (I found in the internet) this setup will have no Radiator cap, the overlflow bottle wis just out of this shot to the right by the Battery location
with the little blue hose going to it ^^ Lower middle of this image
Next is a WRX but still similar setup (another random Image from the internet)
No Rad cap, Header tank on the Driver side and over flow is not quite visible
until