I have a 99 A4 with 100k and need some help on the best way to flush the coolant. I looked all over the form and could not find anything. I was wondering if I should use a bottle of that Prestone flush. The coolant looks like sleuge in the car so I now I need to flush it all out. If
any one has done a full flush at home please help.

Thanks

 

The service manual states to drain the coolant, fill with water (I would use distilled) and then run the motor till warm. Drain and repeat until the water is clear. When I did this on my C4, I let it cool before draining so it actually took me a few days to finish the procedure. I was nervous about draining a hot block.

Then re-fill 50% capacity with Dexcool. Both Dexcool and distilled water are cheap at Wal Mart. I wouldn't personally use a flush.

 

I drained the radiator and filled with distilled water, than ran car till it reached temp. Did this Approx 5 times or till the Drained water ran Clear.The system holds approx. 13 Qts, So I used About a Gallon and a half of Dex cool and topped off with Distilled Water to get about a 55% mixture.

 

If the procedure below is not followed a low or high coolant level condition and/or vehicle damage could result.


Park the vehicle on a level surface.
Follow the steps below to remove the radiator surge tank fill cap:
Slowly rotate the cap counterclockwise1/4 turn and then stop. Do not press down..
Allow any residual pressure, indicated by a hissing sound, to be relieved.
After all hissing stops, continue turning counterclockwise to remove the cap.
To tighten the cap, use hand tight pressure only.
Open the radiator drain ****.
Allow the system to drain completely.
Inspect the engine coolant:
Discolored -- follow the flush procedure below.
Normal in appearance -- Continue with the next step.
Close the radiator drain ****.

Important
When filling the cooling system use a 50 to 60 percent concentration with DEX-COOL® coolant.


Fill the system through the surge tank opening.
Fill half the capacity of the system with 100 percent DEX-COOL® coolant.
Slowly add clean drinkable water to the system until the level reaches to the base of the neck.
Start the engine.
Idle engine for 1 minute.
Install surge tank cap.
Cycle the RPM, idle to 3000 in 30 second intervals until engine coolant reaches 99°C (210°F).
Shut off the engine.
Refer to step 3 above to remove the surge tank cap.
Start the engine.
Idle engine for 1 minute and fill surge tank to 1/2 inch above COLD FULL mark on the radiator surge tank.
Install the surge tank cap.
Cycle the RPM, idle to 3000 in 30 second intervals until engine coolant reaches 99°C (210°F).
Shut off the engine.
Top off coolant as necessary, 1/2 inch above FULL COLD mark on the radiator surge tank.
Rinse away any excess coolant from the engine and the compartment.
Inspect the concentration of the coolant.
Flush Procedure

Important
Do not use a chemical flush.


Block the drive wheels.
Place the transmission in Park or Neutral.
Engage the parking brake.
Run the engine until the thermostat opens.
Stop the engine.
Follow the drain and fill procedure using only clean drinkable water repeat if necessary until the fluid is nearly colorless. Refer to the drain and fill procedure.
Fill the cooling system. Refer to the drain and fill procedure.

This is the exact procedure used from GM service information. This is how the flush and fill procedure should be performed by dealership personnel.
HOWEVER, I would question the need for the flush.
Unless you are experiencing deposits on the filler neck to the surge tank, or you have about 100k or the vehicle has been coolant tested, and it is breaking down, I would not bother.
As long as the coolant is not low for an extended period of time, I would suspect that you are doing just fine.
At least test the coolant first, to make sure.

 

oh yeah buy the Pre-mix DexCool and save yourself the trouble of mixing it

 

What a suprise to find the white plastic plug vs. a conventional plug or drain. Used a 1/4" drive extension to open it. After 6 years/ 60,000 miles the fluid was redish but clean with no sediment or discoloration. I drained the coolant. started the engine and ran it for about 60 seconds watching the temp gauge. When the temp passed 190 I turned it off and the coolant began to drain again. I took out 11 qts with a 12 qt capacity. Replacement was distilled water and Havoline GM coolant at 60/40 blend. Easiest change I ever made. I didn't flush because everything was so clean. Filling was easy. After filling until it would take no more,, I started the engine until temps hit 190,, turned it off,, then topped off. Signed off in my Maint book,,, job done. The most difficult part was jacking the front AND rear to be level for the job. Piece of cake.. easy job .. 99 Nassau blue

 

Thanks for all the great information.

 

I used to run the Dexcool in my C4. I had the motor apart one winter to polish all the aluminum. While drained, I borrowed an articulating boroscope from work and went into the block and into the radiator. It was absolutely spotless. Everything I have read to date indicates that as long as you keep at least 50% mixture and don't let the system get low, this stuff works great. My block inspection certainly proved that out.