24/7 Customer service
To make aftermarket auto parts an afterthought.
Add your vehicle
Address
Login
Cart
Item
$0.00
Add your vehicle to ensure fitment/Choose a yearRequired Fields
Select a different vehicle
Make/Model
VIN
Save

Audi Thermostat

211 items

Upgrade your vehicle's thermostat with A-Premium's high-quality options. Choose reliability and durability for a smoother ride.

  • All filters
  • Sort By
  • Year
  • Model
  • Price
  • Placement on Vehicle
  • Brand
  • Material
  • Color
  • Warranty
Vemo V15-99-2081 Engine Coolant ThermostatVemo V15-99-2081 Engine Coolant Thermostat
VemoPart # V15-99-2081
Vemo V15-99-2081 Engine Coolant Thermostat
4.99 Reviews
$102.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2017-2017 Audi Q5, 2017-2017 Audi S5, 2017-2017 Audi S5, 2017-2017 Audi S5, 2017-2017 Audi SQ5, 2016-2017 Audi Q5, 2016-2017 Audi Q5, 2016-2016 Audi S4, 2016-2016 Audi S4, 2016-2016 Audi S4, 2016-2016 Audi S4, 2016-2016 Audi S5, 2016-2016 Audi S5, 2016-2016 Audi SQ5, 2016-2016 Audi SQ5, 2015-2015 Audi A7 Quattro, 2015-2015 Audi A7 Quattro, 2014-2016 Audi S5, 2014-2016 Audi S5, 2014-2016 Audi SQ5
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2081, 06E121111A, 06E121111E, 6E121111A, 6E121111E, TH728185J, 06E121111AD, 06E121111AL, 
...View more
item #1001QNG5
Note
With seal
Show less
Vemo V15-99-2001 Engine Coolant Thermostat
VemoPart # V15-99-2001
Vemo V15-99-2001 Engine Coolant Thermostat
4.99 Reviews
$22.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2009-2009 Audi TT Quattro, 2008-2008 Audi TT Quattro, 2008-2008 Volkswagen R32, 2007-2008 Volkswagen Eos, 2006-2009 Audi A3 Quattro, 2005-2006 Volkswagen Touareg, 2004-2006 Audi TT Quattro, 2004-2006 Porsche Cayenne, 2004-2004 Volkswagen Jetta, 2004-2004 Volkswagen R32, 2004-2004 Volkswagen Touareg, 2003-2003 Volkswagen Jetta, 2002-2002 Volkswagen Jetta, 2001-2003 Volkswagen EuroVan, 2000-2005 Volkswagen Golf, 2000-2000 Volkswagen EuroVan, 2000-2000 Volkswagen EuroVan, 1999-2002 Volkswagen Jetta, 1999-1999 Volkswagen EuroVan, 1999-1999 Volkswagen Golf
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2001, TX3080D, 78544S, 78259S, 5307280, 30480, 55180J, 75121113A, 
...View more
item #1001QRRS
Note
With seal
Show less
Vemo V15-99-2002-1 Engine Coolant Thermostat
VemoPart # V15-99-2002-1
Vemo V15-99-2002-1 Engine Coolant Thermostat
4.99 Reviews
$27.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2015-2015 Volkswagen Jetta, 2013-2013 Volkswagen Jetta, 2013-2013 Volkswagen Jetta, 2012-2013 Volkswagen Jetta, 2011-2015 Volkswagen Jetta, 2011-2013 Volkswagen Jetta, 2011-2011 Volkswagen Jetta, 2011-2011 Volkswagen Jetta, 2011-2011 Volkswagen Jetta, 2011-2011 Volkswagen Jetta, 2007-2010 Volkswagen Golf City, 2007-2009 Volkswagen Jetta City, 2006-2007 Volkswagen GTI, 2006-2006 Volkswagen Golf, 2005-2006 Audi TT, 2004-2005 Volkswagen Jetta, 2004-2005 Volkswagen Passat, 2003-2005 Volkswagen Beetle, 2003-2005 Volkswagen Beetle, 2003-2005 Volkswagen Jetta
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2002-1, 78268S, TX1487D, 5205287, 4154313, 20087, 03G121113, 050121113B, 
...View more
item #1001QS2R
Note
With seal
Show less
Vemo V15-99-1894 Engine Coolant Thermostat
VemoPart # V15-99-1894
Vemo V15-99-1894 Engine Coolant Thermostat
4.99 Reviews
$21.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2005-2005 Volkswagen Passat, 2004-2004 Volkswagen Passat, 2002-2002 Volkswagen Cabrio, 2002-2002 Volkswagen Cabrio, 2002-2002 Volkswagen Cabrio, 2000-2006 Volkswagen Beetle, 2000-2006 Volkswagen Jetta, 2000-2001 Volkswagen Cabrio, 1999-2006 Volkswagen Golf, 1999-1999 Volkswagen Cabrio, 1999-1999 Volkswagen Cabrio, 1999-1999 Volkswagen Jetta, 1999-1999 Volkswagen Jetta, 1998-1999 Volkswagen Beetle, 1998-1998 Volkswagen Jetta, 1998-1998 Volkswagen Jetta, 1998-1998 Volkswagen Jetta, 1997-1998 Volkswagen Cabrio, 1997-1998 Volkswagen Golf, 1997-1998 Volkswagen Jetta
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-1894, TX1387D, 78223S, 5307087, 5301887, 5303587, 23487, 068121113D, 
...View more
item #1001QQD9
Note
With seal
Show less
Vemo V15-99-1990 Engine Coolant Thermostat
VemoPart # V15-99-1990
Vemo V15-99-1990 Engine Coolant Thermostat
4.99 Reviews
$32.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2008-2008 Jaguar S-Type, 2008-2008 Jaguar S-Type, 2007-2009 Jaguar XK, 2007-2009 Jaguar XKR, 2007-2007 Jaguar S-Type, 2006-2009 Jaguar XJR, 2006-2006 Jaguar S-Type, 2006-2006 Jaguar XJ8, 2003-2005 Audi Allroad Quattro, 2001-2002 Audi Allroad Quattro, 2001-2001 Volkswagen Passat, 2001-2001 Volkswagen Passat, 2001-2001 Volkswagen Passat, 2001-2001 Volkswagen Passat, 2000-2004 Audi A6 Quattro, 2000-2002 Audi S4, 1999-1999 Audi A4, 1999-1999 Audi A4 Quattro, 1999-1999 Audi A6, 1999-1999 Audi A6 Quattro
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-1990, TX3087D, 78410S, 5305987, 30487, 067121113, 078121113D, 25121113F, 
...View more
item #1001QPCT
Show less
Vemo V15-99-2069 Engine Coolant Thermostat
VemoPart # V15-99-2069
Vemo V15-99-2069 Engine Coolant Thermostat
4.99 Reviews
$42.99
Low stock: Only 4 left
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2017-2017 Audi A5 Quattro, 2017-2017 Volkswagen Tiguan, 2017-2017 Volkswagen Tiguan, 2016-2016 Volkswagen Eos, 2015-2016 Audi A4, 2015-2016 Audi A4, 2015-2016 Audi A4 Quattro, 2015-2016 Audi A4 Quattro, 2015-2016 Audi A5 Quattro, 2015-2016 Audi A5 Quattro, 2015-2015 Audi A4, 2015-2015 Audi A4 Quattro, 2015-2015 Audi A5 Quattro, 2015-2015 Audi A6, 2015-2015 Volkswagen Eos, 2014-2016 Volkswagen Tiguan, 2013-2016 Audi allroad, 2013-2015 Audi A6 Quattro, 2013-2015 Audi A6 Quattro, 2013-2014 Audi A6
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2069, 78742, 862031695, TX11795D, TX12395D, 06J121113, 6J121113, 6J121113A, 
...View more
item #1001QQ5S
Note
With seal
Show less
Vemo V15-99-2046 Engine Coolant Thermostat Kit
VemoPart # V15-99-2046
Vemo V15-99-2046 Engine Coolant Thermostat Kit
4.99 Reviews
$65.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2013-2014 Volkswagen Beetle, 2012-2014 Volkswagen Jetta, 2011-2014 Volkswagen Golf, 2010-2013 Audi A3, 2010-2010 Volkswagen Golf, 2010-2010 Volkswagen Jetta, 2009-2014 Volkswagen Jetta
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2046, TI3387, 9025907, 03L121111AC, 03L121111AM, 03L121111M, 3L121111AC, 3L121111M
item #1000XCYZ
Note
Without gasket/seal, With thermostat
Show less
Vemo V15-99-0004 Engine Coolant Thermostat Housing
VemoPart # V15-99-0004
Vemo V15-99-0004 Engine Coolant Thermostat Housing
4.99 Reviews
$142.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2005-2005 Volkswagen Passat, 2003-2005 Audi Allroad Quattro, 2003-2004 Volkswagen Passat, 2002-2005 Volkswagen Passat, 2002-2005 Volkswagen Passat, 2002-2005 Volkswagen Passat, 2002-2004 Audi A6 Quattro, 2002-2002 Volkswagen Passat, 2001-2002 Audi Allroad Quattro, 2001-2001 Audi A6, 2001-2001 Audi A6 Quattro, 2001-2001 Audi A6 Quattro, 2001-2001 Audi A6 Quattro, 2001-2001 Volkswagen Passat, 2001-2001 Volkswagen Passat, 2001-2001 Volkswagen Passat, 2001-2001 Volkswagen Passat
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
MaterialPlastic
item #1001QPYW
Note
Without thermostat
Show less
Vemo V15-99-2058 Engine Coolant Thermostat
VemoPart # V15-99-2058
Vemo V15-99-2058 Engine Coolant Thermostat
4.99 Reviews
$39.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2005-2007 Volkswagen Touareg, 2005-2006 Audi A8 Quattro, 2004-2006 Audi A8 Quattro, 2004-2006 Volkswagen Phaeton, 2004-2004 Volkswagen Touareg, 2003-2004 Audi RS6, 2002-2003 Audi S6, 2001-2003 Audi S8, 2000-2004 Audi A6 Quattro, 2000-2003 Audi A8 Quattro
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2058, 216187312, TX3487D, 5304487, 077121113C, 22687, VT22687, TX3482D, 
...View more
item #1001QPEK
Note
With seal
Show less
Vemo V15-99-2003 Engine Coolant Thermostat
VemoPart # V15-99-2003
Vemo V15-99-2003 Engine Coolant Thermostat
4.99 Reviews
$19.99
Low stock: Only 5 left
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2005-2005 Volkswagen Passat, 2003-2004 Volkswagen Passat, 2002-2005 Volkswagen Passat, 2002-2005 Volkswagen Passat, 2002-2005 Volkswagen Passat, 2002-2002 Volkswagen Passat, 2001-2001 Audi A6, 2001-2001 Audi A6 Quattro, 2001-2001 Audi A6 Quattro, 2001-2001 Volkswagen Passat, 2001-2001 Volkswagen Passat, 2001-2001 Volkswagen Passat, 2001-2001 Volkswagen Passat, 2000-2001 Audi A4, 2000-2001 Audi A4 Quattro, 2000-2000 Audi A6, 2000-2000 Audi A6 Quattro, 2000-2000 Volkswagen Passat, 2000-2000 Volkswagen Passat, 2000-2000 Volkswagen Passat
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2003, TX3092D, 214592312, 214592, 65497T, 78401S, 78401, 30492, 
...View more
item #1001QQRL
Show less
Vemo V15-99-2067 Engine Coolant Thermostat Kit
VemoPart # V15-99-2067
Vemo V15-99-2067 Engine Coolant Thermostat Kit
4.99 Reviews
$101.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2011-2012 Audi Q5, 2011-2011 Audi A6, 2010-2010 Audi A5 Quattro, 2010-2010 Audi A5 Quattro, 2010-2010 Audi A6, 2009-2012 Audi Q5, 2009-2012 Audi Q5, 2009-2010 Audi Q5, 2008-2009 Audi A5 Quattro, 2008-2008 Audi A4, 2007-2009 Audi A4 Quattro, 2006-2008 Audi A6, 2006-2008 Audi A6 Quattro, 2006-2008 Audi A6 Quattro, 2006-2007 Audi A4, 2005-2008 Audi A4 Quattro, 2005-2008 Audi A4 Quattro, 2005-2005 Audi A4 Quattro, 2005-2005 Audi A4 Quattro, 2005-2005 Audi A4 Quattro
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2067, 50688, 862021688, 1601479182, TH698988, 06E121111M, 6E121111D, 6E121111G, 
...View more
item #1000X6Z7
Show less
Vemo V15-99-2022-1 Engine Coolant Thermostat Kit
VemoPart # V15-99-2022-1
Vemo V15-99-2022-1 Engine Coolant Thermostat Kit
4.99 Reviews
$80.99
Low stock: Only 3 left
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2008-2009 Audi TT, 2008-2009 Volkswagen Eos, 2008-2009 Volkswagen Eos, 2008-2008 Volkswagen Eos, 2008-2008 Volkswagen Jetta, 2008-2008 Volkswagen Passat, 2008-2008 Volkswagen Passat, 2008-2008 Volkswagen Passat, 2007-2007 Volkswagen Eos, 2006-2008 Audi A3, 2006-2008 Volkswagen GTI, 2006-2008 Volkswagen Jetta, 2006-2007 Volkswagen Jetta, 2006-2007 Volkswagen Passat
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2022-1, 132887, 187901, 78680, 5353087, 58087, 1601325913, 06F121111F, 
...View more
item #1000XCSC
Note
With seal
Show less
Vemo V15-99-2053 Engine Coolant Thermostat Housing
VemoPart # V15-99-2053
Vemo V15-99-2053 Engine Coolant Thermostat Housing
4.99 Reviews
$43.99
Low stock: Only 4 left
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2018-2018 Audi A5 Quattro, 2018-2018 Audi A5 Quattro, 2018-2018 Audi A5 Quattro, 2018-2018 Audi A5 Quattro, 2018-2018 Audi A5 Quattro, 2018-2018 Audi A5 Quattro, 2018-2018 Audi A5 Quattro, 2018-2018 Audi A5 Quattro, 2018-2018 Audi A5 Sportback, 2017-2018 Audi A4 allroad, 2017-2018 Audi A4 Quattro, 2015-2015 Volkswagen Jetta, 2015-2015 Volkswagen Jetta, 2014-2014 Audi TT Quattro, 2014-2014 Volkswagen Jetta, 2014-2014 Volkswagen Jetta, 2014-2014 Volkswagen Jetta, 2014-2014 Volkswagen Jetta, 2014-2014 Volkswagen Jetta, 2013-2014 Volkswagen Jetta
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2053, 1K0121113A
item #1001QQWK
Show less
Vemo V15-99-2107 Engine Coolant Thermostat Housing
VemoPart # V15-99-2107
Vemo V15-99-2107 Engine Coolant Thermostat Housing
4.99 Reviews
$536.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2017-2017 Audi A4, 2017-2017 Audi A4 allroad, 2017-2017 Audi A4 Quattro, 2017-2017 Audi A6 Quattro, 2017-2017 Audi Q7, 2017-2017 Volkswagen Golf Alltrack, 2016-2017 Audi A6, 2016-2017 Audi TT Quattro, 2016-2017 Audi TTS Quattro, 2016-2017 Volkswagen Golf, 2016-2017 Volkswagen Golf SportWagen, 2016-2017 Volkswagen GTI, 2016-2016 Audi A6 Quattro, 2015-2017 Audi A3, 2015-2017 Audi A3 Quattro, 2015-2017 Audi S3, 2015-2017 Volkswagen Golf R, 2015-2015 Volkswagen Golf SportWagen
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2107, 06K121605, 06L121111P, 06L121012A, 06L121131, 06L121012H, 06L121111J, 06L121111L, 
...View more
item #1001QN05
Show less
Vemo V15-99-2110 Engine Coolant Thermostat Housing
VemoPart # V15-99-2110
Vemo V15-99-2110 Engine Coolant Thermostat Housing
4.99 Reviews
$193.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2015-2016 Audi A3, 2015-2016 Audi A3, 2015-2016 Audi A3, 2015-2015 Volkswagen Beetle, 2015-2015 Volkswagen Golf, 2015-2015 Volkswagen Golf, 2015-2015 Volkswagen Golf, 2015-2015 Volkswagen Golf SportWagen, 2015-2015 Volkswagen Golf SportWagen, 2015-2015 Volkswagen Golf SportWagen, 2015-2015 Volkswagen Jetta, 2015-2015 Volkswagen Jetta, 2015-2015 Volkswagen Jetta, 2015-2015 Volkswagen Passat, 2015-2015 Volkswagen Passat
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2110, 04L121026J, 04L121026AH, 04L121113D, ­04L121026J, 4L121026F, 04L121026AE, 04L121026E, 
...View more
item #1001QS0P
Note
With thermostat, Pre-Assembled
Show less
Vemo V15-99-2028 Engine Coolant Thermostat
VemoPart # V15-99-2028
Vemo V15-99-2028 Engine Coolant Thermostat
4.99 Reviews
$49.99
Low stock: Only 5 left
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2010-2010 Audi A8 Quattro, 2007-2011 Audi S6, 2007-2009 Audi A8 Quattro, 2007-2009 Audi A8 Quattro, 2007-2009 Audi S8
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2028, TH580, 191980, 9025133, W0283, TH713580J, 4E0121113, 1430877
item #1001QRQU
Show less
Vemo V15-99-2068 Engine Coolant Thermostat
VemoPart # V15-99-2068
Vemo V15-99-2068 Engine Coolant Thermostat
4.99 Reviews
$80.99
Low stock: Only 4 left
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2017-2017 Audi A5 Quattro, 2017-2017 Audi A5 Quattro, 2017-2017 Audi A5 Quattro, 2017-2017 Audi A5 Quattro, 2017-2017 Audi Q5, 2017-2017 Volkswagen CC, 2017-2017 Volkswagen Tiguan, 2017-2017 Volkswagen Tiguan, 2017-2017 Volkswagen Tiguan, 2017-2017 Volkswagen Tiguan, 2017-2017 Volkswagen Tiguan, 2017-2017 Volkswagen Tiguan, 2017-2017 Volkswagen Tiguan, 2016-2017 Audi Q3, 2016-2017 Audi Q3 Quattro, 2016-2016 Audi A4, 2016-2016 Audi A4 Quattro, 2016-2016 Audi A4 Quattro, 2016-2016 Audi A4 Quattro, 2016-2016 Audi A5 Quattro
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2068, 78743, CTI0010, 06H121119B, 06H121119BS1, 6H121119BS1, 6H121119B, 34782, 
...View more
item #1001QLDH
Show less
Vemo V15-99-2043-1 Engine Coolant Thermostat Housing
VemoPart # V15-99-2043-1
Vemo V15-99-2043-1 Engine Coolant Thermostat Housing
4.99 Reviews
$67.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2017-2017 Audi Q3 Quattro, 2016-2016 Audi Q3, 2015-2015 Audi Q3
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-2043-1, 3L121111AE, 03L121111AL, 03L121111AE
item #1001QPE0
Show less
Vemo V15-99-1985-1 Engine Coolant Thermostat
VemoPart # V15-99-1985-1
Vemo V15-99-1985-1 Engine Coolant Thermostat
4.99 Reviews
$19.99
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 1997-1997 Volkswagen EuroVan, 1996-1997 Audi S6, 1995-1996 Volkswagen EuroVan, 1995-1995 Audi S6, 1995-1995 Volkswagen EuroVan, 1993-1993 Volkswagen EuroVan, 1993-1993 Volkswagen EuroVan, 1993-1993 Volkswagen EuroVan, 1992-1994 Audi S4, 1991-1992 Audi 80, 1990-1992 Audi 80 Quattro, 1990-1991 Audi 100, 1990-1991 Audi 100 Quattro, 1990-1991 Audi 200, 1990-1991 Audi 200 Quattro, 1990-1991 Audi 90, 1990-1991 Audi 90 Quattro, 1990-1991 Audi Coupe Quattro
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-1985-1, 78256S, TX2580D, TX2587D, 5302687, 30487, 075121113D, 075121113E, 
...View more
item #1001QLTU
Note
With seal
Show less
Vemo V15-99-1905 Engine Coolant Thermostat Kit
VemoPart # V15-99-1905
Vemo V15-99-1905 Engine Coolant Thermostat Kit
4.99 Reviews
$157.99
Low stock: Only 5 left
Enter ZIP codeFree standard shipping
3-year warranty
90 days free return
Fits 2005-2005 Audi A4 Quattro, 2005-2005 Audi A4 Quattro, 2005-2005 Audi A4 Quattro, 2004-2005 Audi A4 Quattro, 2004-2005 Audi A4 Quattro, 2003-2006 Audi A4, 2002-2005 Audi A4, 2002-2005 Audi A4 Quattro, 2002-2005 Audi A4 Quattro
Add Trim and Engine info to ensure a guaranteed fit
Vehicle: Audi
Item LocatedUnited States
Quantity1
Part interchange
V15-99-1905, TM3100, 177403, 5348203, 601100, 06B121111F, 06B121111L, 6B121111F, 
...View more
item #1000XC9K
Note
With seal, With sensor
Show less
Page 10 of 11

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.

Related Blogs

Why Does Coolant Boil After You Turn the Engine Off?

Learn why coolant boils or bubbles after you turn the engine off, how heat soak affects the cooling system, and how to diagnose leaks, trapped air, cap, thermostat, fan, water pump, or head gasket problems.

Jul 29, 2026