Genuine Audi TT Thermostat

Audi TT Thermostat Parts and Q&A

• Thermostat
  050-121-113-C
  Q: How to remove and install the Thermostat in an engine on Audi TT?

  A:

  With the engine fully cold, remove the cap from the coolant expansion tank, disconnect the battery ground strap from the negative terminal, and remove the upper and lower engine sound insulation panels. Drain the coolant, then turn fasteners to remove the sound insulation panels from the left side of the engine compartment. Disconnect the air hose at the throttle valve control module, the harness connector from the mass air flow sensor, and the air cleaner mounting bolts to remove the air cleaner assembly. Release the retaining tabs and pivot the fuse box upward while keeping the electrical wires connected, then disconnect the fuse box from the carrier at the rear hinge and position it out of the way using a tie wrap. Remove the mounting bolts and the fuse box carrier, then disconnect the vacuum hose from the intake manifold change-over valve and remove the mounting bolts and the intake manifold change-over assembly. Working at the front left side of the engine, disconnect the engine coolant temperature sensor harness connector, then disconnect the secondary air hose and move it out of the way. Disconnect the coolant hoses at the indicated connections, remove the mounting bolts and the bracket for the secondary air hoses, and the mounting bolt on the bracket for the wiring harness. Remove the thermostat housing, pushing the coolant pipe toward the coolant pump to prevent it from being removed, then remove the O-ring and thermostat from the housing. Install in reverse order of removal, noting the installation position of the thermostat and replacing the O-ring and gaskets.
• Thermostat
  050-121-113-B
  Q: What happens when a thermostat is stuck open or closed, and how can the thermostat be accurately tested on Audi TT?

  A:

  An open thermostat will cause the engine to warm up slowly and generally run below normal operating temperature at highway speed. A closed thermostat will restrict coolant flow to the Radiator and cause overheating. The thermostat to be tested must first be removed and after that placed in a container of hot water (temperature is noted by an accurate thermometer) to monitor the temperature at which it first starts to open and the temperature at which it is fully open. To see if the thermostat opens and whether coolant is circulating through the radiator, you can let a cold engine run at idle (while warming up). As the coolant temperature rises, feel the heater and expansion tank hoses. They will get hot. The radiator hoses - especially the lower hose - should remain cool to touch. The radiator hoses should warm quickly when the thermostat opens, with the radiator fan cycling on soon afterwards. If the radiator hoses are not hot, the thermostat either has not opened or the radiator is clogged. If the radiator hoses are hot but the fan did not come on, check the radiator fans with the wiring diagrams.