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Audi A4 Thermostat Replacement
 
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Pelican Technical Article:

Audi A4 Thermostat Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$10 to $80

Talent:

***

Tools:

10mm socket and extensions, pliers, flathead screwdriver, large bucket

Applicable Models:

Audi A4 (2002-05)
Audi A4 Cabriolet (2003-06)

Parts Required:

Thermostat, gasket, coolant

Hot Tip:

Work on a cold engine

Performance Gain:

Engine runs at the proper temperature

Complementary Modification:

Replace older hoses

The thermostat helps control the engines temperature. If your car is running too hot and there is the proper amount of coolant in the car and it is not leaking, or your car is taking a long time to warm up, there is a very good chance your thermostat is bad and needs to be replaced. The thermostat in the Audi A4 is sealed in the housing and cannot be replaced separately.

The thermostat on the Audi A4 is locating in located below the intake manifold and behind the alternator. To replace the thermostat you will need to drain the coolant and move the lock carrier to the service position. Please see our articles on these procedures for additional instruction.

If you are going to be working on the thermostat, make sure the car is cool and not under pressure. Working on a hot engine or one under pressure can cause serious harm and should never be attempted. Coolant is also very toxic and needs to be collected and disposed of in accordance with your local regulations as pouring coolant down a drain or into the street is illegal. Also, be sure to wash your hands thoroughly after working around it.

If the coolant in the car is new there is no reason to replace it as long as you drain it into a clean container. Coolant is expensive and not to great for the environment so if the coolant in your car is good, try and save it for reuse.

Disconnect the ground strap from the battery terminal (red arrow) and place the cable where it cannot accidentally come in contact with the battery while working.
Figure 1

Disconnect the ground strap from the battery terminal (red arrow) and place the cable where it cannot accidentally come in contact with the battery while working. Otherwise, you will be working around live electric wires. If you happen to touch the lead going to the alternator against something, you can cause permanent damage to the electrical system if the battery is hooked up. Be smart here and disconnect it. For more information please see our article on battery replacement.

With the lock carrier in the service position use a 17mm wrench and rotate the tensioner clockwise (red arrow) to the open position and insert the locking key or a 5mm Allen to keep it open (yellow arrow).
Figure 2

With the lock carrier in the service position use a 17mm wrench and rotate the tensioner clockwise (red arrow) to the open position and insert the locking key or a 5mm Allen to keep it open (yellow arrow). Slip the belt off the alternator (green arrow).

Since you have already drained the coolant, use a set of pliers and remove the coolant hose from above the battery to give you more room to work (red arrow).
Figure 3

Since you have already drained the coolant, use a set of pliers and remove the coolant hose from above the battery to give you more room to work (red arrow).

Use a 6mm Allen and remove the four bolts holding the alternator in place (red arrows).
Figure 4

Use a 6mm Allen and remove the four bolts holding the alternator in place (red arrows).

Slide the alternator forward and release the clip on the wiring connection (red arrow) and separate the connection.
Figure 5

Slide the alternator forward and release the clip on the wiring connection (red arrow) and separate the connection.

Use a 13mm wrench and remove the main strap (red arrow).
Figure 6

Use a 13mm wrench and remove the main strap (red arrow). You can now remove the alternator from the engine. Installation of the new alternator is the reverse of removal.

Directly behind the alternator is the thermostat and thermostat housing.
Figure 7

Directly behind the alternator is the thermostat and thermostat housing. There are three hoses and one sensor attached to the housing. Use a set of pliers and remove the upper hose (yellow arrow). There is also the metal coolant tube (green arrow) and lower coolant hose (red arrow).

Separate the plug from the coolant temperature sensor by unclipping it and pulling it off (yellow arrow).
Figure 8

Separate the plug from the coolant temperature sensor by unclipping it and pulling it off (yellow arrow). Next use a flathead screwdriver and unclip the quick disconnect wire (red arrow) on the hose to thermostat housing connection. Wiggle and slide the lower hose off of the housing; these can get really stuck and sometimes it is easier to remove the housing from the block and then separate the hose.

Use a 10mm socket and remove the single screw holding the metal coolant tube to the housing.
Figure 9

Use a 10mm socket and remove the single screw holding the metal coolant tube to the housing. There is a very good chance you will need to use a screwdriver to pry the tube from the housing (red arrow).

Remove the two 10mm Allen bolts that connect the housing to the engine block (red arrows).
Figure 10

Remove the two 10mm Allen bolts that connect the housing to the engine block (red arrows).

With the thermostat housing out you can see how the actual thermostat is contained in the housing (red arrow).
Figure 11

With the thermostat housing out you can see how the actual thermostat is contained in the housing (red arrow). This photo also illustrates the clip and coolant temperature sensor attached to the housing (yellow arrow).

Always replace the gasket even if you are reinstalling the old housing (red arrow).
Figure 12

Always replace the gasket even if you are reinstalling the old housing (red arrow).

Before installing the new thermostat and housing make sure to check the mounting area to insure it is clean and level.
Figure 13

Before installing the new thermostat and housing make sure to check the mounting area to insure it is clean and level. Most important is to make sure the old O-ring gasket is not still in the block. Installation is the reverse of removal. Do NOT forget to replace the coolant.




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Comments and Suggestions:
Swanie Comments: How much should this cost if u go to a mechanic ????
April 11, 2016
  Followup from the Pelican Staff: I am not sure what the repair will cost in your area. Call a few shops and ask for a quote. It is also a good idea to have them confirm what the issue is.
- Nick at Pelican Parts
 

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