Signs That Your Car Thermostat Is Broken
A car's thermostat allows coolant to enter the engine when the engine reaches normal operating temperature. The thermostat also allows warm coolant to enter the heater core, which allows the car's heater to blow warm air. If your thermostat is not working properly, you could experience significant engine damage or no heat in your car on cold mornings.
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Cold Heat
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If the thermostat is not opening properly, warm coolant is unable to enter the heater core, and the heater will blow only cold or moderately warm air. If the car's interior does not get very warm if the heater is on the highest setting, the thermostat is probably stuck closed, or there is a blockage close to the heater core. If the thermostat fails only partially, you could have warm heat when driving in the city; but when on the highway, the temperature could fall, resulting in less heat.
Temperature Gauge Variance
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A broken thermostat can fail in several positions. Most thermostats fail in a position somewhere between open and closed, meaning that coolant gets to the engine at all times, even when the engine is not yet at its normal operating temperature. If the thermostat fails in an open position or partially open, you will find the temperature gauge is below where it normally falls. A thermostat can also fail in the closed position, which prevents all coolant from entering the engine. This will result in the engine exceeding its operating temperature as evidenced by the temperature gauge rising quickly. If this happens, pull the car to the side of the road and wait for a tow truck.
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Lower Gas Mileage
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If you notice a sharp decline in your car's gas mileage, the engine may be running too cold as happens when the thermostat is stuck open. By preventing the vehicle from operating at its normal temperature, the engine may run rich, which uses more fuel.
Steam from the Engine
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If the thermostat fails in a closed or semi-closed position, it will keep coolant from entering the engine, causing the engine to overheat. This could cause steam, so stop the vehicle quickly if you see steam rising from the engine.
Fluctuation in Temperature
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Once your vehicle is at normal operating temperature, check to see if the gauge position varies based on driving conditions. If the temperature goes down when you are accelerating or at normal speed but goes up when you are in traffic, the thermostat is probably faulty. If the temperature fluctuates, the thermostat is probably stuck partially open.
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References
- Photo Credit yellow car, a honda japanese sport car model image by alma_sacra from Fotolia.com
