Thermostat Inspection

WARNING: This page is about a different car, the 2011 Suzuki SX4. However, it is still accessible from the selected car via links, so may be relevant.

Reference: THERMOSTAT REMOVAL AND INSTALLATION

Make sure that air bleed valve (1) of thermostat is clean.
Check to make sure that valve seat (2) is free from foreign matters which would prevent valve from seating tight.
Check thermostat gasket (3) for breakage, deterioration or any other damage.

Fig 1: Identifying Thermostat Gasket And Air Bleed Valve
Courtesy of SUZUKI OF AMERICA CORP.
Check thermostatic movement of wax pellet as follows:
1. Immerse thermostat (1) in water, and heat water gradually.
2. Check that valve starts to open at specific temperature.
  Temperature at which valve begins to open
  
  80 - 84 °C (176 - 183 °F)
  
  Temperature at which valve become fully open
  
  95 - 97 °C (203 - 206 °F)
  
  Valve lift
  
  More than 8 mm (0.31 in.) at 95 °C (203 °F)

If valve starts to open at a temperature substantially below or above specific temperature, thermostat unit should be replaced with a new one. Such a unit, if reused, will bring about overcooling or overheating tendency.

Fig 2: Checking Thermostatic Movement

Courtesy of SUZUKI OF AMERICA CORP.