The engine cooling system may be disturbed by faulty thermostats. It may result in problems with the engine's overheating or overcooling. When a thermostat malfunctions, it is typically either stuck open or closed. We covered can a Bad Thermostat cause a Blown Head Gasket in great depth in the last post. We'll talk about the stuck open or closed thermostat in this article, along with its symptoms. Stuck open and Stuck closed thermostat: A thermostat that is stuck open means that the main or primary valve is stuck in the open position. As a result, even at lower temperatures, coolant is continuously circulating through the radiator. The following illustration shows what happens to a car's engine cooling system when a thermostat is left open. When the thermostat's main valve is jammed closed, the thermostat is considered to be in a stuck-closed condition. As a result, even above the predetermined temperature, the coolant is not permitted to circulate through the radiator. The coolant flow with a stuck-closed thermostat is seen in the figure below. Symptoms of Stuck Closed Thermostat: 1] The Temperature Gauge Quickly Increases: A stuck-closed thermostat prevents coolant from flowing through the radiator. The coolant never cools as a result. The engine's temperature increases more quickly as a result of it. 2] Engine Overheating: The thermostat is stuck closed, which causes the engine to overheat more quickly. It can result in the engine trouble number P0217 and the 'Check Engine' light turning on. 3] Coolant Leaks: If the thermostat is jammed closed, hot coolant may escape through the thermostat housing, coolant hose, radiator, etc. 4] Unusual Engine Noise: Because the coolant does not flow through the radiator, it heats up to the boiling point. Due to the coolant boiling, it makes an odd noise. 5] One Heated and One Cold Hose: When the engine gets hotter, check the radiator's inlet and output hoses. The thermostat may be jammed closed if one of the hoses is noticeably cooler than the other. It is simple to identify a jammed closed thermostat using this technique. Symptoms of Stuck open thermostat: 1] The 'Check Engine' light illuminates: When the thermostat is jammed open, the coolant is continuously circulated through the radiator. The prolonged cooling makes it difficult to reach the ideal engine temperature. Error code P0128 appears on the "check engine" light as a result. 2] The temperature gauge on the dashboard rises considerably more slowly than usual. Reduced gas mileage: The engine runs below its ideal temperature as a result of the ongoing cooling. The engine burns more fuel as a result of the incomplete combustion of the fuel. As a result, the fuel economy is decreased. 4] Ineffective interior temperature heater operation: The heated engine coolant is used to warm the internal air of the vehicle. Therefore, the heater performs poorly as a result of the lowered coolant temperature. 5] Even at lower temperatures, the coolant beneath the radiator cap swirls: Start the engine after opening the radiator cap when the engine is cold. The thermostat is likely stuck in the open position if the radiator coolant is swirling.