16/10/2026
Automotive thermostat
AAC AUTOMOTIVE
03 93599343
A car thermostat is a small valve that regulates engine temperature by controlling the flow of coolant between the engine and the radiator.
How It Works
• Cold Engine: The thermostat stays closed so coolant circulates only inside the engine, helping it warm up fast.
• Warm Engine: Once the engine reaches operating temperature (usually around 82°C to 91°C), a wax pellet inside the thermostat melts and expands, pushing the valve open.
• Radiator Flow: Coolant flows into the radiator to release heat before returning to the engine.
Common Signs of a Bad Thermostat
• Stuck Open: The engine runs too cold, and the cabin heater takes a long time to warm up.
• Stuck Closed: The engine overheats rapidly, or the dashboard temperature gauge spikes.
• Erratic Readings: The temperature gauge jumps up and down unexpectedly.
what happens when car thermostat fails
When a car thermostat fails, it either gets stuck closed or stuck open, disrupting how coolant flows between the engine and the radiator.
Thermostat Stuck Closed
When the thermostat cannot open, coolant cannot reach the radiator to shed heat.
• Rapid overheating: The temperature gauge quickly spikes into the red zone.
• Steam and pressure: You may see steam under the hood, bubbling in the coolant reservoir, or sweet-smelling coolant odors.
• Severe engine damage: Continuing to drive an overheating engine can warp cylinder heads, crack the engine block, or blow the head gasket.
Thermostat Stuck Open
When the thermostat stays stuck open, coolant flows through the radiator constantly. The engine struggles to reach its proper operating temperature (typically 180°F to 220°F).
• Overcooling: The temperature gauge stays low or takes a very long time to rise.
• Poor cabin heat: The heater blows cold or lukewarm air because the coolant never gets hot enough to warm the interior.
• Bad fuel economy: The engine computer senses a cold engine and keeps the fuel mixture "rich," burning extra fuel and increasing emissions.
• Carbon buildup: Incomplete fuel combustion over time leads to carbon deposits and increased engine wear.
Common Signs and Warning Lights
• Erratic temperature readings: The gauge jumps up and down unpredictably as the valve catches or fails intermittently.
• Check engine light: Your car's computer may trigger diagnostic trouble codes like P0128 (coolant thermostat below regulating temperature).
• Coolant leaks: Pressure buildup from overheating can force coolant past seals or hoses around the thermostat housing.
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03 9359 9343
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