Coolant / antifreeze flush for VW TDI
Difficulty 2/5
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Introduction

Coolant is lifetime rated, suggested change interval: 100,000+ miles or as needed, depending on use.  Since some coolant is lost during a water pump change, you'll end up draining most of it with the timing belt service.  This is enough to refresh the coolant, no flush is needed as long as you stick to G12 spec coolants.  Many high mileage cars report totally clean coolant passages with G12, even after 200,000+ miles!

Warning:  do not mix red, pink, or purple VW coolant with green or blue coolant or other non-VW/Audi OEM or OEM compatible coolant!  If your coolant is brown, a few things are possible.  You could have an oil leak at the EGR cooler, oil cooler, or head gasket.  Another possibility is that someone mixed incompatible coolants together.  In this case, the entire system should be flushed at least twice before adding new coolant.  Flush once with distilled water and then with G12/distilled water.  Or drain and refill with G12/water and do the same the next weekend.  If you have contaminated coolant, don't worry about driving your car for now because nothing will break immediately due to mixed coolant only.  Just get to a mechanic or flush the system twice as soon as practical.  It might not look dark if you take a small sample, but if it is not pink or purple colored through the coolant reservoir plastic, then it is probably brown.  Pictured below is what coolant will look like if it is contaminated.  The color is not Prestone-neon green or the correct light red/pink/purple.

Note about VW coolant.  There are 3 specs available: G12, G12+, and G12++.  G12 (VW# g012-a8f-a4) is compatible with G12+ (VW# g012-a8f-m1) but G12+ is being discontinued.  The replacement for G12+ is G12++ (VW# g012-a8g-m1) and it's not yet clear what G12++ is compatible with.  Pentosin is generic VW coolant compatible with G12/G12+, compatibility with G12++ is not yet known but it should mix.

Also note that you should never use any radiator stop leak products.  Although the TDI turbo is oil cooled only, as good practice, stop leak products can gum up the turbo coolant lines and possibly cause damage to the turbo and engine.

Parts

Coolant capacity: 6.0 Liters of coolant/distilled water
Ratio: anywhere between 60% coolant/40% distilled water and 40% coolant/60% distilled water
Coolant type: VW G-012-A8F-M1 (ZVW 237 G12) or Pentosin G12 (pink color) available from TDIparts.com , worldimpex.com
and/or (pink and purple coolant are compatible) VW G-012-A8F-A4 or Pentosin g12+ (G12 plus, purple color) available from TDIparts.com , worldimpex.com

Enough coolant and distilled water to satisfy the required 6 liters.  Make sure to get a little extra to account for any spills.

Warning:  coolant is poison.  Wear waterproof gloves, and take all precautions to avoid skin or eye contact.  If some spills on your driveway, rinse it off with water because animals may drink the coolant and become poisoned.  Also note all warnings and precautions on the coolant and in the factory service manual.

Suggested tool: hose clamp pliers, they can fit into a tight spot and lock the clamp open

Procedure

Draining the coolant

Engage the parking brake, jack up the front of the car using the factory jack points, rest car securely on jack stands, chock the rear wheels, and make sure the car is safe and secure before doing anything else.  Remove lower belly pan and engine top plastic cover.

The idea is that you want to open a low spot to let the coolant out and refill it as necessary.  If your fluid is still fresh and clean, you can just open the lower radiator hose and refill as necessary.  If your fluid is dirty and contaminated or you want to switch from pink to green or vice versa, you need to flush a few times to get as much coolant out as possible.  Remember, G12 and G12+ are compatible only with each other and water!

Open coolant reservoir cover (first picture) and place catch pan below coolant drain on the radiator bottom. The drain is plastic, so be careful!  I suggest using a hose to catch the fluid and guide it into the catch pan.  This is a good time to check for coolant migration, a rare but very serious condition effecting the wiring harness.  See 1000q: coolant migration for more details.

Attach drain hose to coolant drain and place in catch pan. Let drain.  If you want, you can apply pressure to the overflow tank filler opening to get additional fluid out.  This drains only the radiator and coolant overflow tank.

To drain the coolant out of the engine block, remove coolant hose from oil cooler (bottom of oil filter assembly outlined in green) and let drain.

To refill coolant:

If you are flushing the system completely, refill with distilled water and the flushing cleaner.  It's best to use only distilled water but you can use filtered tap water as long as you plan on a final flush later with distilled water but since distilled water is so cheap I would just use all distilled water.  Warm up the engine and leave the heater on hot or high to get the coolant out of the heater core.  Let the engine cool down and drain.  Do not add cool water to a hot engine because draining the hot coolant can scald you.  Refill and repeat as needed.  The last flush should be distilled water only.  Then continue to the normal refill steps.

For a normal refill, first mix coolant with only distilled water.  Tap water contains minerals that will collect on the cooling system, damaging the metal and reducing coolant efficiency. Also note that you cannot mix generic green, orange, or blue coolant with g12 or g12+ red or purple VW coolant!  It will turn brown and sludge.  Make sure you mix the coolant in a ratio of between 40- 60% water and the rest of the solution coolant.

Put back and secure any hoses or drains that you loosened earlier.  Unclamp the hose outlined in green in the picture below and pull that end back.  I suggest using this hose because it's small and easy to remove, and it's at a high point of the radiator and engine.  You can use any high spot, I just use this hose because it's easy to reach and it's high in the coolant circuit.  As you add coolant/water to the coolant reservoir, air will slowly come out this hose until the liquid reaches that level.  Obviously, when liquid starts coming out of the hose, reattach and re-clamp the hose.  During this stage, the engine should NOT be running!

At this point you may be asking yourself why not just add coolant into the reservoir on an empty coolant system and let the engine run and let the coolant it pump itself and gradually bleed out the air?  Because that would take longer and let the water pump start on a dry system.  It would not be lubricated by the coolant and it would also cause lots of air bubbles and cavitation, causing you to misjudge the coolant level and eroding the pump.  Believe it or not, air bubbles at the water pump can erode the water pump and cause excess vibration over time, maintaining a proper level of coolant prevents water pump failure.

Recheck that the radiator drain and all clamps have been retightened, and the coolant level is between max and min.

Test drive to normal operating temperature and check the coolant level again.  If it didn't go down, you got all the air out.  If the level went down, wait until the car is cool and then add coolant/water until the level is between mix/max.  If you open the reservoir while the coolant system is hot, scalding coolant will spray out everywhere, so do not open the coolant system while hot!

Check for any leaks, put everything back, double check everything, and you're done!

 

 

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