Wrong reading on analog temperature gauge.cold start reads imediate 50 %gain on temp gauge

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?