Heater Hose Clamp Problem

Those clamps should fit the hose just snug. Slips on about like a wedding band. Todays hoses probbly do have a smaller OD. :(
The clamp is positioned to sit just below the bung on the fitting.
If you push the clamp far down the fitting it could leak.
Those type clamps were the original quick connect or quick assembly atleast.
They applied a small amout of adhesive to the inside of the hose to first lubricate then seal after they shoved the hose with clamp into place. That adhesive was is the same stuff we used to glue patches on inner tubes.
To scuff the shine off of the inside hose wall will help too.