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Audi A6 C6: How to Replace Coolant

Coolant is essential for keeping your engine in running order, and if you don't have it replaced, you could be riding in a shoulder bound car. Coolant should be replaced every 90K miles, here's how to do it yourself.

By Jack Plageman - May 4, 2016

This article applies to the Audi A6 C6 (2004-2011).

The coolant in your car helps keep your engine running smoothly. The fluid is a mix of half water and half antifreeze that moves throughout the engine, keeping it at a good operating temperature. If you notice the temperature gauge going into the red zone, steam from the engine, leaking fluid under your car, or if cold air comes out of your vents instead of hot, then it is likely time to replace your coolant. You don't have to spend the money to take it to a shop, as you can do it yourself in the comfort of your garage. All it takes it a little knowledge and being okay with getting dirty.

Audi A6 C6: How to Replace Coolant

Materials Needed

  • Jack and stands
  • Bucket/catch pan
  • Gloves
  • Hot water
  • G12 Coolant

Step 1 – Jack your car up and find the radiator hose

Using a jack, lift the car up so that there is enough space to fit a bucket underneath and secure the car with a jack stand. The radiator hose is located on the left side of the radiator core. If there is not enough space to get a bucket underneath, then a drip pan will work (however, you may need more than one). Also, you will want to open the hood and remove the reservoir cap and leave it off while you are completing the job.

audi a6 coolant radiator hose petcock drain draincock how to replace change drain
Figure 1. This is where the cap is for draining the coolant.

Step 2 – Find and open the drain cock

Underneath the car and on the radiator hose, locate the drain cock. It has an end that twists and one with a spout on it; once you open the drain, the coolant will come out of the spout. Before you open it, though, you should make sure the bucket is placed below the spout so no coolant falls on the ground. After you have opened it, the coolant will drain into the bucket.

audi a6 coolant radiator hose petcock drain draincock how to replace change drain
Figure 2. This is what the drain cock looks like.

Pro Tip

To open the drain cock, first, turn it 90 degrees and pull a little. Then, turn it another 90 and pull again. However, it should be noted that the plug does not come out all of the way, so do not pull to hard or it may break.

Step 3 – Flushing the coolant out

After the coolant has finished draining into the bucket, you can start flushing any leftover fluid out. Seal the drain cock and then fill the coolant reservoir with hot water and put the cap back on. Then start the car and put the fan on high heat, but low speed. Once hot air starts coming out of the vents, shut the car off and remove the reservoir cap to vent the air out. After that you need to drain the coolant again by opening the drain cock and letting the coolant come out.

Pro Tip

You may need to complete this step multiple times before all of the old coolant is drained. You can stop once the fluid has become diluted and is more aqueous.

Step 4 – Adding the new coolant

At this point, you've sufficiently flushed out any and all coolant from your cooling system. Ready your G12 OEM coolant and gallons of distilled water. Mix a 50/50 mixture of coolant and distilled water. Start with about two gallons of 50/50 mixed coolant for the time being, and fill your radiator overflow tank until it reaches the max line. Leaving the cap off, start your Audi's engine and set the cabin's heater to max temperature, lowest fan setting and let the car idle for about 15 minutes. Doing so will expunge any trapped pockets of air bubbles from the cooling system that can cause overheating. Refill the reservoir to just below the max line if the level has dropped. After this, refit the overflow cap and take the car for a test drive to ensure that there is no overheating.

Pro Tip

If there is still cold air coming out of the vents or if the engine seems to overheat after replacing the coolant, you need to get rid of the air in the system. To do this, start the car and let it warm up, then shut it off, and while it is still warm, open the reservoir cap and let it vent. You should be wearing gloves for this step.

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