AudiWorld Forums

Audi A4 B7: How to Replace Thermostat

The thermostat in the Audi A4 is designed to open up when the engine reaches its optimal temperature; failing to open can cause the engine to overheat.

By Bassem Girgis - March 24, 2016

This article applies to the Audi A4 B7 (Pre-2008).

The thermostat is designed to block the way between the radiator and the engine. As the Audi A4's engine reaches the optimal temperature, the thermostat opens up to let coolant run through the radiator. The coolant works to keep the engine cool and prevents it from overheating. Every now and then, the thermostat can go bad, which will prevent it from opening up. Once the thermostat fails to open, the engine's temperature rises, and if you continue to drive, it could very well overheat. Read on to learn how to replace the old, faulty thermostat.

Audi A4 B7: How to Replace Thermostat

Materials Needed

  • Socket set
  • Wrench
  • Flat head screwdriver
  • Pliers
  • Drain pan
  • Thermostat

Step 1 – Remove serpentine belt

Use your 17mm wrench to push the tensioner down, this will allow the belt to come loose. Remove the belt, then let go of the tensioner.

AUDI A3 A4 B7 B8 2.0T COOLANT RADIATOR THERMOSTAT REPLACE REMOVE CHANGE HOW TO
Figure 1. Loosen the tensioner and remove the belt.

Step 2 – Remove the alternator

Disconnect your negative (black) battery terminal. The alternator is held in place by four 6mm hex bolts. You can access all four of them from the side. Use your socket to remove them. Remove the electrical connection on the alternator. You can do so by pressing on the plastic tab, then pulling it out. Finally, remove the nut on the back of the alternator that connects another wire to it. Pull the alternator out.

  • AUDI A3 A4 B7 B8 2.0T COOLANT RADIATOR THERMOSTAT REPLACE REMOVE CHANGE HOW TO
    Figure 2. Remove four screws.
  • AUDI A3 A4 B7 B8 2.0T COOLANT RADIATOR THERMOSTAT REPLACE REMOVE CHANGE HOW TO
    Figure 3. Remove electrical connection.
  • AUDI A3 A4 B7 B8 2.0T COOLANT RADIATOR THERMOSTAT REPLACE REMOVE CHANGE HOW TO
    Figure 4. Remove rear wire.

Step 3 – Remove radiator hose

Remove the radiator hose on top of the thermostat assembly. First, use a flat head screwdriver to loosen the worm clamp, then pull the hose up. Feel free to plug the hose with a rag to avoid any extra mess.

AUDI A3 A4 B7 B8 2.0T COOLANT RADIATOR THERMOSTAT REPLACE REMOVE CHANGE HOW TO
Figure 5. Remove radiator hose.

Step 4 – Lower radiator hose

Use your pliers to pull the clip off of the lower radiator hose, then pull the hose off with your hand. You will have to wiggle it a few times to remove it.

AUDI A3 A4 B7 B8 2.0T COOLANT RADIATOR THERMOSTAT REPLACE REMOVE CHANGE HOW TO
Figure 6. Remove lower radiator hose.

Step 5 – Remove coolant lines

There are a couple of coolant lines connected to the thermostat, so remove the three bolts holding these lines in place. Use your pliers to slide the radiator hose's clamp off of the lower hose connected to the thermostat, and put the drain pan under the car to catch the coolant that is about to drain. Grab the coolant lines and the radiator hose, and pull them away from the thermostat, then wait for the coolant to drain.

  • AUDI A3 A4 B7 B8 2.0T COOLANT RADIATOR THERMOSTAT REPLACE REMOVE CHANGE HOW TO
    Figure 7. Remove bolts holding lines.
  • AUDI A3 A4 B7 B8 2.0T COOLANT RADIATOR THERMOSTAT REPLACE REMOVE CHANGE HOW TO
    Figure 8. Remove bolts holding lines.
  • AUDI A3 A4 B7 B8 2.0T COOLANT RADIATOR THERMOSTAT REPLACE REMOVE CHANGE HOW TO
    Figure 9. Remove bolts holding lines.

Step 6 – Remove thermostat

The thermostat is held down by two 10mm bolts. Remove those, then pull the thermostat out.

  • AUDI A3 A4 B7 B8 2.0T COOLANT RADIATOR THERMOSTAT REPLACE REMOVE CHANGE HOW TO
    Figure 10. Remove bolts holding thermostat in place.
  • AUDI A3 A4 B7 B8 2.0T COOLANT RADIATOR THERMOSTAT REPLACE REMOVE CHANGE HOW TO
    Figure 11. Remove thermostat.

Step 7 – Install new thermostat

Installation is the reverse of removal.

  • Install the new thermostat, then tighten the two bolts holding it in place.
  • Install the radiator hose on top of it, then slide the clamp on it.
  • Install the three bolts holding the coolant lines.
  • Install the other two radiator hoses you removed.
  • Install the alternator in place, then connect the two electrical connections on the back of it.
  • Push the tensioner down, then install the belt back in place.
  • Connect the battery.
  • Refill the radiator with coolant, start the car, then refill it again.

Featured Video: Thermostat Replacement

Related Discussions