Subaru 2003 Impreza - Manual (Page 341)

IMPREZA(NA) A1850BE-A (ENGLISH)
Maintenance and service
11-18
WARNING
Never attempt to remove the radiator cap until
the engine has been shut off and has cooled
down completely. Since the coolant is under
pressure, you may suffer serious burns from a
spray of boiling hot coolant when the cap is
removed.
4. Install the under cover.
Non-turbo models
1) Filler neck
2) Fill up to this level
Turbo models
1) Filler neck
2) Fill up to this level
5. Slowly pour the coolant and fill to the radiator fill-
er neck. Do not pour the coolant too quickly, as this
may lead to insufficient air bleeding and trapped air
in the system.