I had same if you remember in my sedan and I got radiator rodded and a new cap. The coolant loss was minimal but I also noticed staining on my starter motor.
Went through efforts of Bonnet vent (which did reduce under bonnet temps) and shrouding radiator from the front to force air through rad only)
Ended.up being heater core had leak that ended up filling,my foot well.

Small things are amazing how big an impact they can have