You probably have a bad head gasket on your engine.
Location of coolant temperature sensor on a 2003 Mercury Grand Marquis?Read more: Location_of_coolant_temperature_sensor_on_a_2003_Mercury_Grand_Marquis
how to changing engine coolant on a 1993 mercury grand marquis gs.
According to the 2004 Mercury Grand Marquis Owner Guide : The engine cooling system capacity is ( 18 liters / 19 U.S. quarts ) It came from the factory with a 50 / 50 mix of antifreeze and distilled water
For a 1987 Mercury Grand Marquis : For the 5.0 liter / 302 cubic inch V8 engine ( 7.5 quarts of antifreeze with 7.5 quarts of preferably distilled water should give you a 50 / 50 mix of engine coolant ) --------------------------------------------------------------------------- For the 5.8 liter / 351 cubic inch ( 8.0 quarts of antifreeze )
A 1999 Mercury Grand Marquis came from the factory with a 50 / 50 mix of distilled water and ( GREEN color antifreeze , meeting Ford specification ESE-M97B44-A )
The thread on cap on the engine coolant reservoir is the " radiator cap " on a 1995 Mercury Grand Marquis
According to the 2003 Mercury Grand Marquis Owner Guide : It originally came from the factory with a 50 / 50 mix of distilled water and Motorcraft Premium Gold Engine Coolant ( that's YELLOW color , meeting Ford specification WSS-M97B51-A1 )
On a 1997 Mercury Grand Marquis : The thread on cap on the engine coolant reservoir is the 16 PSI pressure cap / radiator cap
A 1992 Mercury Grand Marquis would have come from the factory with a 50 / 50 mix of distilled water and GREEN color antifreeze ( meeting Ford specification ESE-M97B44-A )
According to the 1998 Mercury Grand Marquis Owner Guide : The engine cooling system capacity is ( 13.3 litres / 14.1 U.S. quarts ) So a 50 / 50 mix of distilled water and antifreeze would require : ( 6.65 litres / 7.05 U.S. quarts of distilled water and the same amount for the antifreeze )
Heater core leaking.
Mercury Grand Marquis was created in 1983.