Hello Ronald, in order to understand what happens when a thermostat gets stuck open, it is useful to appreciate the role of a thermostat in your car engine.
A thermostat is a thermistor or heat-activated gate valve which regulates the flow of coolant between the engine and radiator. This helps to keep the engine running at an acceptable or normal operating temperature.
When a thermostat is stuck open, engine coolant will flow through the radiator continuously. This will delay engine warm-up and prevent it from reaching the efficient normal operating temperature. The temperature gauge will remain low.
A thermostat stuck open can reduce fuel economy. A constantly cold-running engine will cause the ECU to enrich the fuel mixture, assuming that the engine is cold and needs warming up. This is what causes higher fuel consumption. This situation is similar to when some mechanics decide to remove and eliminate an old or damaged thermostat instead of replacing it with a new one.
There are other engine problems associated with a thermostat stuck-open condition, such as increased emissions, reduced engine performance and premature engine wear when the engine runs below the normal operating temperature.
An engine is less likely to quickly get damaged when the thermostat is stuck open. Damage to the engine happens over time due to the increased emissions and inefficient running.
On the other hand, when the thermostat is stuck closed, the engine is likely to experience instantaneous damage due to severe overheating. Therefore, prolonged driving with the thermostat stuck closed should be avoided.
A visit to a garage to establish if the thermostat is faulty should be your next move, and getting it checked sooner rather than later will help you avoid more costly repairs while restoring your engine’s efficiency and performance.