What are the symptoms of a faulty Audi thermostat?
2 Answers
Automobile thermostat failure symptoms include excessively high or low temperature gauge readings and the thermostat failing to open. Detailed explanation of high/low temperature gauge readings: The most obvious symptom appears on the coolant temperature gauge. If the thermostat's main valve opens too late, it causes engine overheating; if it opens too early, it prolongs engine warm-up time, resulting in excessively low engine temperature that affects performance. Abnormal temperature gauge readings (either too high or too low) may indicate thermostat malfunction. Thermostat failing to open: The temperature gauge shows high temperature readings with elevated engine temperature, but the radiator coolant remains cool to touch, with no noticeable heat from the radiator. Methods to diagnose thermostat failure: After starting the engine, check the coolant reservoir filler opening for coolant flow. Absence of flow indicates either thermostat damage or foreign objects obstructing the main valve. Temperature comparison between upper and lower radiator hoses can also help diagnosis - after 3 minutes of engine operation, properly functioning thermostats will show temperature differences (typically warm upper hose and cool lower hose).
That day when I drove my Audi A4 out, I immediately noticed something wrong with the coolant temperature gauge. Even after driving cold for twenty minutes, the needle was still hovering in the low-temperature zone. The heater couldn't blow out warm air either, leaving my feet freezing. Later on the highway, it got even worse—suddenly the temperature shot up to the red line, and white steam was pouring out from the engine bay. After inspection, it turned out the thermostat was stuck in the open position, causing the coolant to circulate in a full loop the entire time, making it impossible for the engine to warm up. What's even more annoying is that when this part fails, it drastically increases fuel consumption. Since the engine can't reach its optimal operating temperature, it burns at least two extra liters per 100 kilometers. I remember seeing a Q5 at the repair shop last time with the same issue—the cooling fan was spinning like crazy, making a noise like a helicopter. In the end, they had to replace the thermostat to fix it.
