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How to Replace the Thermostat in an 2004 Optra

by Curtis Von Fange

The thermostat controls the operating temperature of an engine. A thermostat that is stuck closed will not let coolant circulate through the radiator and will cause the engine to overheat. A thermostat stuck open will not let the engine reach normal operating temperature. The result is wasted fuel and poor engine performance.

Ensure that the engine and cooling system are cold. Open the drain cock at the bottom of the radiator and let the coolant drain into the pan. Unscrew the radiator cap to release any vacuum on the system. Remove the upper radiator hose at the thermostat housing using a pair of pliers to compress the retaining clamp. Remove the capscrews holding the thermostat housing to the cylinder head. Remove the thermostat and seal from the housing by pressing the mounting flange down and rotating the thermostat clockwise.

Inspect the thermostat housing for small pits and cracks. If present, replace the housing to prevent leakage. Clean the housing, the cylinder head mating surface and the capscrews with a small brush, cleaner and rag. The radiator hose should be clean and pliable without any internal residue, cracking or stiffness. Clean the end inside and out with the rag and some soapy water. The coolant should be clean with no rust, oil or cloudiness. If you intend to reuse coolant, strain it through some clean nylon hose to remove any loose debris or dirt.

Securely install the thermostat in the housing along with a new seal. A light smear of petroleum jelly will lubricate the seal and keep it from accidentally tearing while installing. Put a light coating of thread sealer on the capscrews and torque to 11 foot-pounds. Reconnect the upper radiator hose and seat the clamp. Make sure the drain cock is closed and refill the system with clean coolant. Start the car and bring it up to operating temperature with the heater on full. Check for leaks.

Tips

  • A small hose connected to the drain cock will help control draining the coolant.
  • Releasing the radiator cap after opening the drain cock will also help reduce spillage.
  • Don't use a powerful solvent like brake cleaner on the radiator hose; it dissolves rubber.
  • Cleaning all parts thoroughly will reduce the risk of leaks.

Warnings

  • Do not remove the radiator cap while the engine and the radiator are hot. The heat causes the system to remain under pressure. Removing the cap may release scalding water and steam.
  • Clean up any spilled coolant. It is highly poisonous to animals.

Items you will need

References

About the Author

Curt Von Fange, an ASE Master Automotive Technician, began writing in 1998. His first article related a memorable experience about panning for gold with his father. It was published by "Gold Prospector Magazine" the following year. An associate degree in heavy equipment repair from Ferris State College helps him write numerous technical articles for trade magazines and webzines like YTtractors.com and Desertusa.com.

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Photo Credits

  • radiator humor image by John Sfondilias from Fotolia.com