The thermostat is located on the front of the engine under the elbow at the end of the radiator hose
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left side of dash
Mercury Grand Marquis was created in 1983.
Because the plastic housing is cracked. That is what happened to mine.
Check the engine end of the upper radiator hose
On a 1999 Mercury Grand Marquis : The Original Equipment engine cooling thermostat would have been ( around 192 * Fahrenheit )
firewall 4 - 8 3 - 7 2 - 6 1 - 5 front of 2002 Mercury Grand Marquis
On a 1999 Mercury Grand Marquis , 4.6 liter V8 engine : The Original Equipment engine cooling thermostat would be : ( around 192 * Fahrenheit )
Follow your upper radiator hose back to the thermostat housing(sometimes called a water outlet adapter), which is held on with two bolts. Remove the two bolts and nside the housing is the thermostat and a O-ring seal.
next to the crank pulley
On a 1993 Mercury Grand Marquis ( which is OBD I , EEC IV ) ( there should be an EEC TEST connection in the engine compartrment )