heater blows cold air
What you describe in your 4 words I can deduce there is no water/coolant getting in to your heater core, either because of linkage to valve in heater hose or valve its self
I have had 2 Gran Marquis in my life and both blow barely warm air. My experience: After many years of just barely enough warm air in the Jersey winters, I was in Midas for an oil change and they recommended -in an attempt to get any kind of repair- a cooling system flush. I did it and that was the answer....blows deliciously warm now. Good luck......
Looking for a Used Grand Marquis in your area?
CarGurus has 1,729 nationwide Grand Marquis listings starting at $1,700.
Search Mercury Grand Marquis Questions
Mercury Grand Marquis Experts
Related Models For Sale
Used Cars For Sale