Thermostat stuck closed

The thermostat, when closed, keeps the coolant in the engine until it reaches a certain temperature. If the thermostat is stuck closed, the coolant will remain in the engine rather than circulate to the radiator where it cools. This can lead to overheating as the heat from the engine will not dissipate.

Table of Contents

• 1. Symptoms
  • 1.1 Heater Blows Cold Air Always
  • 1.2 Engine Overheats
  • 1.3 Temperature Gauge Always High or Rises Steadily

Symptoms

Heater Blows Cold Air Always

If the heater is always blowing cool air, the thermostat may be stuck closed. If the coolant cannot circulate out of the engine, it cannot reach the heater core. This will prevent the air from being heated prior to entering the passenger compartment.

Note: This can only occur if the thermostat is between the heater core and engine. Most vehicles have the heater core between the thermostat and engine to provide warm air to passengers as quickly as possible.

Engine Overheats

If the engine routinely overheats, the thermostat may be stuck closed. The coolant will remain in the engine and will continue to heat without being cooled.

Temperature Gauge Always High or Rises Steadily

The temperature gauge measures the coolant temperature. If the coolant is trapped in the engine, its heat will not dissipate and the temperature gauge will continue to rise and remain high.