msu_johnny ... 99 grand marquis
Overheating + cooling system pressure build-up sometimes
indicate a head gasket problem. *Though a pressure and/or combustion-gas test should be done on the cooling system
Do you have oil in the coolant ?
Do you have anti-freeze in the oil ?
Alternative ... Air pocket in the cooling system.
Regarding the no-heat ... Plugged heater core and/or air pocket in the cooling system | blend-door issue (?).