can you tell me the: senser that is bad and the loction on the engine.the car doesn t over heat or loose fluid.still provides heat.year 1995 4 door.
The sender is most likely in the area where the upper radiator hose is attached to the engine.
Look for a single wire with a rubber boot & simply pull it off of the sender.
If the gauge now reads full cold replace the sender.
To simulate a hot engine shove a nail in the rubber boot & ground it to the engine. The gauge should now read full hot
Please tell us the year of your Mercury.
Is it a Marquis, or a “Grand” Marquis?