1990 Ford Mustang 2.3 L Install Thermostat

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If your temperature gauge begins to malfunction, such as reading normal when the engine is obviously overheating or not reading a temperature at all, then you must replace the thermostat in your car's engine. The thermostat controls the amount of coolant that flows around the engine by opening and closing according to the engine temperature. It is essential that you have a working thermostat, or your Mustang could overheat and damage the engine. You can install a thermostat on a 1990 Ford Mustang 2.3-liter car in under an hour.

Tools Used[edit]

Wrench and socket set
Thermostat housing gasket

Install Thermostat[edit]


  • Park the Mustang on a level surface. Turn the engine off and engage the parking brake. Open the engine hood and disconnect the negative cable from the battery.
  • Remove the radiator fill cap by hand, and set it to the side.
  • Slide a bucket under the radiator drain cock (on the driver's-side edge of the radiator). Reach down and open the drain cock by turning it counterclockwise with a wrench and socket. Drain the coolant until you can see the top of the radiator fins when you look inside the radiator. Close the drain cock.
  • Follow the hose that comes off the top of the radiator (on the driver's side) to where it connects to the metal thermostat housing, which is mounted on the water pump.
  • Remove the two bolts holding the housing onto the water pump, using a wrench and socket. Pull the thermostat housing away from the water pump.
  • Pinch the raised center of the thermostat that is inside the housing and turn it counterclockwise until it unlocks. Pull the old thermostat out of the housing. Remove the gasket underneath.


  • Lay the new gasket inside the thermostat housing (exactly where the old one was).
  • Install the thermostat into the housing, making sure that the side with the spring coil is going into the housing.
  • Turn the thermostat clockwise until you feel it lock into place.
  • Set the housing back into position on the water pump, and replace the two mounting bolts. Tighten the bolts with a socket wrench one turn past being hand-tight.
  • Top off your radiator with fresh coolant, and replace the fill cap. Reconnect the battery and close the hood.

Tips & Warnings[edit]

  • There are more options for a thermostat for a 2.3-liter 1990 Ford Mustang than just an OEM replacement. Thermostats come in a variety of temperature ranges, so pick the one that best suits the amount of driving you do and the climate you are in.
  • Never remove or Install thermostat on a vehicle that has been recently driven. The coolant can reach boiling temperature quickly and cause severe burns.