Symptoms of a Faulty Thermostat in Jetta?

[LeilaDella]

Jetta thermostat failure symptoms are as follows: 1. Thermostat malfunction with insufficient opening affects the engine's large and small circulation cycles, preventing effective heat dissipation and causing engine coolant temperature to rise; 2. Excessive thermostat opening leads to low engine coolant temperature, slow temperature rise, increased fuel consumption, and abnormal engine noises; 3. Thermostat sticking tends to cause carbon buildup, resulting in unstable engine idle speed and engine vibration. Below is how the thermostat works: 1. The thermostat is a valve controlling coolant flow path. It's an automatic temperature-regulating device typically containing temperature-sensing components that open/close air, gas or liquid flow through thermal expansion/contraction. 2. At normal temperature, the wax remains solid. When water temperature is below 76°C, the main valve closes completely while the bypass valve opens fully, allowing water from the cylinder head to directly enter the water pump via the bypass pipe (called small circulation). As water only flows between pump and water jacket without passing through the radiator and with small flow rate, the cooling intensity is weak.