What Causes the Significant Temperature Difference Between the Upper and Lower Hoses of the Tiguan?
2 Answers
It is likely due to the thermostat not opening, causing the temperature difference between the upper and lower hoses. Below is more information about the thermostat: 1. Introduction: The thermostat automatically adjusts the amount of water entering the radiator based on the coolant temperature, altering the water circulation range to regulate the cooling system's heat dissipation capacity, ensuring the engine operates within the appropriate temperature range. 2. Working Principle: Typically, automotive thermostats are wax-type thermostats. When the coolant temperature is below the specified value, the refined paraffin inside the thermostat's temperature-sensing body remains solid, and the thermostat valve closes the channel between the engine and the radiator under the action of a spring. The coolant returns to the engine via the water pump, performing a small circulation within the engine.
Recently, my Tiguan also encountered the issue of a significant temperature difference between the upper and lower radiator hoses. The upper hose feels scalding hot, while the lower one remains ice cold, which really worries me. After researching and discussing with other experienced owners, I found that the most common cause is a faulty thermostat. The thermostat acts like a gatekeeper for the cooling system—normally, it opens to allow coolant flow and balance temperatures. If it gets stuck and fails to open, the coolant won’t circulate, resulting in a hot upper section and a cold lower one. A malfunctioning water pump could also be a culprit, as improper operation prevents proper coolant circulation. Low coolant levels or air bubbles trapped in the system can cause this temperature discrepancy too. Prolonged operation under these conditions may lead to engine overheating and even damage the cylinder head gasket, increasing repair costs. I recommend regularly checking the coolant level and color, and avoiding mixing different brands of antifreeze. If you notice a large temperature difference, don’t push your luck—head to a 4S shop or a trusted repair facility immediately for diagnosis. Over years of driving gasoline cars, learning these small tips has been a lifesaver, especially on highways where a sudden coolant temperature spike poses serious risks.
