To find the correct thermostat temperature:
1. Check your owner's manual: This is the best place to start. The manual should specify the correct thermostat temperature for your specific engine.
2. Consult a repair manual: A repair manual specific to your 1999 Mercury Grand Marquis (Haynes or Chilton manuals are popular options) will list the specifications, including the thermostat temperature.
3. Look up the thermostat online: You can search online using the year, make, model, and engine size (e.g., "1999 Mercury Grand Marquis 4.6L thermostat temperature"). However, always verify this information with a reputable source like a repair manual or parts store website that cross-references your vehicle's VIN.
Using the wrong thermostat temperature can lead to overheating or poor engine performance. Therefore, it's crucial to use the manufacturer's recommended temperature. Don't guess – find the correct specification using the resources mentioned above.