Similar to human beings, the engine needs to warm up first before starting its work. And the device that is very important during this process is called thermostat. It is essential in controlling the warming up period of the engine. It works in maintaining the level of temperature that is desired by the engine. Thermostat is actually found between the radiator and the engine and stays close when the engine is still in warming up condition. Here, the coolant is prevented to get out of the engine until the desired temperature is achieved. Likewise, the engine is warmed quickly. As the engine reaches 180°F or 195°F, the thermostat then will open in order to allow the fluid inside to flow through the radiator and be cooled. Thermostat actually works by means of the powertrain control module found in some cars while some operates using the off coolant temperature. The thermostat is really important especially in your vehicle’s cooling system. In fact, this is considered as the engine’s temperature controlling device. Considering its functions, its condition actually becomes critical which also causes some symptoms and troubles with the cooling system. While this thermostat is opened, the heater creates a low output which might lead to overheating and poor fuel economy. Similarly, thermostats that cannot open widely may also result to knocking and pinging during accelerating conditions. Faulty or damaged thermostat must be replaced soon. Of course, you must always consider the quality of the product. And that characteristic fits to the Wahler thermostat kit w/two seals that can be used for your 1987 Volkswagen Jetta. Visit or browse our catalog now and get the G4001-13789 Jetta Wahler Thermostat Kit w/Two Seals.