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Shopping for 2003-Audi-A4
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Thermostat

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Thermostat Housing Assembly
A-Premium®
Thermostat Housing Assembly for Audi A4 A4 Quattro 2002-2006
$52.99
Quantity Less than 5
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2-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
MaterialPlastic
ColorBlack
Part interchange
06B121111K, 06B121111H, 06B121111G, 06B121111B, 06B121111D, V15991905, 902814
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Engine Coolant Thermostat Housing Assembly
A-Premium®
Engine Coolant Thermostat Housing Assembly for Audi A4 Quattro A6 Quattro
$22.99
Quantity Less than 4
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2-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
MaterialAluminum
Part interchange
902-5167, 914198, 86207, V15992033, 06C121111C, 06C121111D, 06C121111E
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Beck/Arnley 143-0849 Engine Coolant Thermostat
Beck/Arnley
Beck/Arnley 143-0849 Engine Coolant Thermostat
$29.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
QuantityOne Set
Part interchange
143-0849
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Beck/Arnley 143-0709 Engine Coolant Thermostat
Beck/Arnley
Beck/Arnley 143-0709 Engine Coolant Thermostat
$32.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
143-0709
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Beck/Arnley 143-0816 Engine Coolant Thermostat
Beck/Arnley
Beck/Arnley 143-0816 Engine Coolant Thermostat
$30.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
QuantityOne Set
Part interchange
143-0816
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Beck/Arnley 143-0149 Engine Coolant Thermostat
Beck/Arnley
Beck/Arnley 143-0149 Engine Coolant Thermostat
$19.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
QuantityOne Set
Part interchange
143-0149
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Beck/Arnley 143-0873 Engine Coolant Thermostat Housing Assembly
Beck/Arnley
Beck/Arnley 143-0873 Engine Coolant Thermostat Housing Assembly
$104.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
143-0873
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Beck/Arnley 143-0910 Engine Coolant Thermostat Housing Assembly
Beck/Arnley
Beck/Arnley 143-0910 Engine Coolant Thermostat Housing Assembly
$44.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
143-0910
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Engine Coolant Thermostat - Mahle TI 205 92D
Mahle
Engine Coolant Thermostat - Mahle TI 205 92D
$54.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
TI 205 92D, 4814.92D, 15288, TI20592D, 914-198, 06C 121 111 E
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Engine Coolant Thermostat - Mahle TM 3 100
Mahle
Engine Coolant Thermostat - Mahle TM 3 100
$94.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
TM 3 100, 34047, 48732, 601-212, 06B 121 111 K, TM3100, 1.774.03
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Engine Coolant Thermostat - Mahle TX 14 87D
Mahle
Engine Coolant Thermostat - Mahle TX 14 87D
$22.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
TX 14 87D, 3141.87D, 34762, 14419, 050 121 113 C, TX1487D, 200-192, 1.180.87.302
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Engine Coolant Thermostat - Mahle TX 30 71D
Mahle
Engine Coolant Thermostat - Mahle TX 30 71D
$32.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
TX 30 71D, 4235.71D, TX3071D, 2.145.71.312
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Engine Coolant Thermostat - Mahle TX 30 87D
Mahle
Engine Coolant Thermostat - Mahle TX 30 87D
$28.99
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3-year warranty
90 days free return
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
TX 30 87D, 4236.88D, 33975, 48049, TX3087D, 304-192, 078 121 113 F, 2.145.87.312
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Engine Coolant Thermostat - Mahle TX 30 92D
Mahle
Engine Coolant Thermostat - Mahle TX 30 92D
$27.99
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3-year warranty
90 days free return
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
TX 30 92D, TH6533.92J, 4274.92D, 34779, 13649, 304-198, TX3092D, 078 121 113 G, 
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Vaico V10-8198 Engine Coolant Thermostat Housing
Vaico
Vaico V10-8198 Engine Coolant Thermostat Housing
$16.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
MaterialPlastic
Part interchange
V10-8198, 85134, 18244, 50069, 6B121121L, 6B121121, 06B121121L, 06B121121, 
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Vemo V15-99-2003 Engine Coolant Thermostat
Vemo
Vemo V15-99-2003 Engine Coolant Thermostat
$19.99
Edit ZIP code
3-year warranty
90 days free return
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2003, TX3092D, 214592312, 214592, 65497T, 78401S, 78401, 30492, 
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Vemo V15-99-2002-1 Engine Coolant Thermostat
Vemo
Vemo V15-99-2002-1 Engine Coolant Thermostat
$27.99
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3-year warranty
90 days free return
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Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2002-1, 78268S, TX1487D, 5205287, 4154313, 20087, 03G121113, 050121113B, 
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Vemo V15-99-1990 Engine Coolant Thermostat
Vemo
Vemo V15-99-1990 Engine Coolant Thermostat
$32.99
Quantity Less than 4
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3-year warranty
90 days free return
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
V15-99-1990, TX3087D, 78410S, 5305987, 30487, 067121113, 078121113D, 25121113F, 
...View more
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Vemo V15-99-1905 Engine Coolant Thermostat Kit
Vemo
Vemo V15-99-1905 Engine Coolant Thermostat Kit
$157.99
Quantity Less than 5
Edit ZIP code
3-year warranty
90 days free return
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
V15-99-1905, TM3100, 177403, 5348203, 601100, 06B121111F, 06B121111L, 6B121111F, 
...View more
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ÜRO Parts 06B121121 Engine Coolant Thermostat Housing
ÜRO Parts
ÜRO Parts 06B121121 Engine Coolant Thermostat Housing
$12.99
Edit ZIP code
3-year warranty
90 days free return
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: 2003 Audi A4
Item LocatedUnited States
Quantity1
Part interchange
06B121121, 06B121121L, 06B121121, 147-0043, CH-9991, V10-8198, URO-008057
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Page 1 of 2

What is an engine thermostat?

 While all engines can become too hot, if your thermostat isn't working correctly, your engine's well-being is at serious risk. The engine thermostat, often simply referred to as a thermostat, regulates the engine's operating temperature within an optimal range (typically around 195 to 220 degrees Fahrenheit).

How does a car thermostat work?

As a temperature-sensitive valve within the cooling system, a car thermostat responds to changes in coolant temperature. Understanding how it works by the following breakdown steps:

  • Closed position (cold start)

Initially closed to help the engine warm up quickly.

  • Heating up

The engine generates heat during operation.

  • Opening the thermostat

A temperature-sensitive element (usually wax) causes the thermostat to open gradually.

  • Coolant flow

When open, coolant flows from the engine to the radiator.

  • Maintaining optimal temperature

Adjusts coolant flow to maintain the ideal engine temperature.

  • Temperature regulation

Continuously adjusts to prevent overheating and ensure efficient operation.

Signs of a bad thermostat

  1. Overheating: The engine becomes excessively hot due to a stuck-closed thermostat.
  2. Low or fluctuating temperature: A thermostat stuck open results in a cooler engine, affecting fuel efficiency and heating.
  3. Temperature warning light: Illuminates to indicate engine overheating due to a faulty thermostat.
  4. Poor fuel efficiency: Stuck-open thermostat reduces fuel efficiency as the engine operates less efficiently at lower temperatures.
  5. Inadequate cabin heating: Insufficient cabin heating in cold weather with a thermostat that's stuck open.
  6. Coolant leaks: Gasket or sealing issues can lead to coolant leaks.
  7. Rapid temperature fluctuations: The gauge shows rapid swings between hot and cold.
  8. Engine running hot at idle: Higher engine temperature during idle or in traffic due to restricted coolant flow.
  9. Slow or inconsistent warm-up: Longer-than-normal warm-up times, even in moderate weather.
  10. Inconsistent heater operation: This affects the performance of the vehicle's heater, causing inconsistent or inadequate heating in cold weather.