I looked at motorcraft . com and looked up the 1998 Grand Marquis and it shows :
Coolant Temperature Sensor Connector
Motorcraft part number ( WPT 431 )
Leads : 2 - brown - male
Location of coolant temperature sensor on a 2003 Mercury Grand Marquis?Read more: Location_of_coolant_temperature_sensor_on_a_2003_Mercury_Grand_Marquis
Unplug electric connector. Sensor is in water jacket so you will need to catch coolant after removing sensor. Properly dispose of old coolant. Install new sensor and just make a little snug (with open-end wrench)- do NOT over tighten. Install electric connector and top off coolant.
Disconnect electric connector from sensor. Remove sensor and catch & properly dispose of coolant that leaks out. Install new sensor and use open end wrench to make snug (DO NOT OVERTIGHTEN). Connect electric connector. Top off coolant. Clear DTC and ensure it does not come back (check engine light).
coolant temperature sensor are located where the coolant runs in the block near the thermostat housing normally the connector are on top of the sensor and the sensor itself screws in with a deep socket. The temperature sensor is usaully located where the coolant runs OUT of the engine close to thermostat housing.
The coolant level sensor on a 2.4 L is under front of the coolant reservoir towards the engine. It has a 2-wire connector on it.
If the low coolant message is on and you are certain that the coolant level is up, then you probably have a faulty sensor or sensor connector. The low coolant indicator should turn itself off as soon as the coolant is filled.
The coolant sensor is located approx. 1/2 way down the radiator on the passenger side of the vehicle. Disconnect the electrical connector, Remove the spring clip, pull out the sensor, replace with new sensor, replace the spring clip, connect electrical connector.
To the right of the Coolant temperature sensor. It has 1 wire connector
Follow the upper radiator hose to the thermostat housing. The coolant temperature sensor for the ECU (2-pin connector) is on the driver's side. The temperature sender for the guage (1-pin connector. is on the opposite side.
if it is a 96 like mine it is on the top of the coolant resovoir. it is rounnd and has an electrical connector attached to it
drain a little coolant out,just below sensor.take connector off sensor,unscrew sensor!! be carefull not to bang sensor they are sensitive.when putting on new one, wrap the threads with teflon tape to prevent leaking.
What type of coolant sensor? The below answer is for the coolant LEVEL sensor. The coolant TEMPERATURE sensor on my vehicle is located just next to the thermostat housing. On the front top center area of the engine just behind the radiator. Follow the coolant hoses if you have trouble. On my 1995 Jeep Grand Cherokee the sensor is located on the top of the plastic coolant reservoir tank. Look for a small (2-wire?) electrical connector.