the electric cooling fan stuck ON? the t-stat and new coolant will fix this~
Did you make sure the coolent level is where it should be?
could be low coolant as ronc stated. have seen the blend door actuators fail and fail in between hot and cold causing this issue.
Looking for a Used Grand Marquis in your area?
CarGurus has 2,571 nationwide Grand Marquis listings starting at $1,300.
Search Mercury Grand Marquis Questions
Mercury Grand Marquis Experts