How to Change the Thermostat on GMC Sierra

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If your GMC Sierra is running hot, whether it is over-heating or just running at a higher temperature, then it might be time to replace your thermostat. A thermostat is small but plays a big role in your car’s temperature. When your engine is running and generating heat, your thermostat is hard at work. It opens and closes according to the temperature of your coolant in your engine, in order to regulate the temperature of your vehicle. When one goes bad, it is usually stuck shut or won’t open enough, which traps the hot coolant in the engine, causing it to overheat.

Things You'll Need

  • sockets
  • torque wrench
  • new thermostat and gasket
  • gasket scrapper
  • antifreeze
  • screwdriver

Changing the Thermostat

  • Remove the thermostat from the engine by following the upper radiator hose to where it meets the thermostat housing. The thermostat housing is where the opposite end of the upper radiator hose mounts to the engine.

  • Drain enough coolant from radiator until it is below thermostat. Failure to do this will result in your antifreeze leaking out onto the ground.

  • Loosen clamp and remove radiator hose from thermostat housing. Some antifreeze will leak out: have some rags available. If your engine is a 4.8L, 5.3L, or 6.0L, remove the air inlet duct first.

  • Remove the bolts holding the thermostat housing on and pull the housing from the engine. The gasket might make it a little difficult, so do not be afraid to pull hard, but do not strike it with any tools as you can crack it.

  • Remove old thermostat and note its alignment.

  • Place a rag in the thermostat’s mounting hole so no gasket material can enter the engine and then scrape the gasket from the housing and the engine. Install the new thermostat in same position as old one.

  • Apply a sealant to the thermostat housing, the part you removed, and then the gasket as well.

  • Reinstall the housing and tighten down bolts snugly. Torque them with your torque wrench. If your engine is one of the following then toque them to 21 ft lbs: 4.3L, 5.0L, or 5.7L. If your engine is a 7.4L then torque the bolts to 27ft lbs. If your engine is a 4.8L, 5.3L, or 6.0L then torque the bolts to 11 ft lbs. Make sure you do not over tighten them.

  • Reinstall the radiator hose to thermostat housing and tighten the clamp.

  • Refill the radiator with coolant and start the engine, allowing it to reach normal operating temperature.

  • Check for any leaks at hose connection and thermostat housing. You can tighten them as necessary to stop any leaks.

  • Stop the engine and allow it to cool down completely then check the coolant level. Add coolant as required.

Tips & Warnings

  • Always be careful when working around a hot engine.
  • Never open the radiator or any related components while the engine is hot.
  • Never allow anyone or anything to drink antifreeze, it is poisonous.
  • Never pour antifreeze down a drain, it is against EPA regulations.

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