Quote:
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 (?).

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-click the Vic-