while driving with the heater on, strong fumes in car- had to turn off heater and drive with windows open in freezing temps! think i saw a greenish liquid under car on road after I parked.
Sounds like you may have blown the head gasket and it is leaking on the exhaust, thus the green fluid and the bad smell.
here are some shops:
https://repairpal.com/subaru-repair-in-philadelphia-pennsylvania
RepairPal Certified shops can diagnose and repair your 2001 Subaru Impreza. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.