Coolant antifreeze flush for Volkswagen Jetta TDI 2005 2006

Difficulty 2/5
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This article shows how to flush the coolant system in your 5th generation (mk5) 2005 or 2006 VW Jetta TDI with G12.

The engine coolant is also known as engine antifreeze.  Volkswagen does not give a change interval but it's suggested to change the coolant when you do the timing belt service, or about every 80-100,000 miles.  Most of the coolant will come out when you remove the water pump anyways.   Stick with VW or generic G12 coolant because when used with distilled water, it results in very clean coolant passages and very good operation.  Your coolant should be reddish or light purple in color.  While you are here, also check for coolant migration.

Caution: do not mix VW G12 coolant with green, blue, orange, or any other non G12 compatible coolant or else it can foam or sludge!  There are 3 main types of coolant available: G12, G12+, and G12++.  G12 (VW# g012-a8f-a4) is compatible with G12+ (VW# g012-a8f-m1).  The replacement for G12+ is G12++ (VW# g012-a8g-m1).  Pentosin is generic OEM compatible coolant compatible with G12.

If your coolant is brown, a few things are possible.  You could have a leak in the EGR cooler, oil cooler, or head gasket.  If it looks sooty then it could be residue from an oil fill or the EGR cooler.  If it's the EGR cooler then you should also see coolant residue in the exhaust and see the coolant level dropping.  If it's the oil cooler then the oil and coolant are mixing.  You will see milky engine oil.  Do not drive the car in this condition, immediately change the oil and have oil and coolant flushed.  If it's the head gasket you will notice harder starting, burning coolant, and low compression.  You should also notice immediate pressurization of the coolant reservoir on a cold engine.  (Pressurization of the reservoir on a warm engine is correct).  It's also possible that there's a tiny leak between the oil and coolant head gasket passage and not the cylinder, which will not effect compression.  Another possibility is that someone mixed incompatible coolants together. 

If the oil is contaminated, have it fixed immediately since contaminated oil can cause engine damage.  If you only have minor coolant contamination don't worry about driving the car because what's done is already done and nothing will immediately blow up.  If you see scales or gummy buildup on the inside of the coolant tank then do not drive - have the system flushed as soon as possible since the contamination could lead to overheating and engine damage.  Contaminated coolant might not look dark if you take a small sample but if it isn't pink/ purple/red through the coolant reservoir plastic, then it's probably brown.  Pictured below is contaminated coolant.

Also note that you should not use 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.

Never dispose of used engine antifreeze or coolant onto the ground or into the water!  If you can't find a dump, can search for a local waste disposal.


Coolant capacity: 6.0 Liters of coolant/distilled water
Ratio: anywhere between 60% coolant/40% distilled water and 50% coolant/50 distilled water, higher coolant ratio provides better freezing protection
Coolant type: VW G-012-A8F-M1 (ZVW 237 G12) or Pentosin G12 (pink color) available from kermatdi 1.5L size
and/or (pink and purple coolant are compatible) VW G-012-A8F-A4 or Pentosin g12+ (G12 plus, purple color)

Enough concentrated 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.  If you pollute, at least dilute.  Also note all warnings and precautions on the coolant and in the factory service manual.

hose clamp remote operated pliers since they can fit into a tight spot and lock the spring clamp open


General tip - before firmly pulling hoses off, twist them.  This will break the seal and make it much easier to pull the hose off.  Don't jerk or pry the hoses with a screwdriver

If your fluid is still pink and clean, you can just open the lower radiator hose and the oil cooler hose and refill as necessary.  If your fluid is dirty and contaminated or you want to switch from pink to green coolant or vice versa, see the below section on thoroughly flushing the coolant system.

Draining the coolant

The service manual may say that there's a drain on the radiator.  Mine didn't.  Use the hose clamp pliers to remove the hose clamp on the lower radiator.  This will drain the radiator only - there is still coolant in the engine and cabin heater.

Also remove  the coolant reservoir tank cap to let air into the system.  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.

Remove the plastic engine cover - it just pops straight up and off.

To drain the coolant out of the engine, remove one of the coolant hoses on the oil filter housing.  You will need the remote operated hose clamp pliers here.  Twist the hose with pliers before trying to pull it off.  This will break the seal.  Be careful to not tear the hoses.

Lightly reinstall either the radiator hose or the hose your just removed to drain the engine.  Apply compressed air at the coolant reservoir hose to blow out as much coolant as possible.  Remove the hoses and let any coolant out.

Most of the coolant will be drained out of the cabin heater when you blew air into the system.  If you still want to drain it, reach behind the engine and disconnect the 2 hoses going into the firewall.  These lead to the cabin heater.  They are hard to reach so there aren't pics here.

Thoroughly flushing the coolant system

If you want a thorough flush, use a hose to fill and refill the system.  You can also leave one of the lower hoses open while flushing the system with water at another spot.  This will circulate water through the system.   There will always be corners where there is lingering coolant but as long as the coolant is not contaminated, don't worry about a little old coolant.  Just drain and refill.  The last flush should be with distilled water - run the engine with a closed coolant system and this will help circulate the coolant.

If your coolant is contaminated you need to flush a few times with first water, then radiator flush/water, then distilled water to circulate the cleaner thoroughly.  Also drive the car with the water/cleaner mix to open the thermostat and circulate the cleaners.  If it's really bad, accept that you'll have to do a flush again when you have time or take it to a professional.  They have access to better radiator flush machines and chemicals, it's easy for them to dispose of the used fluids, and it's relatively inexpensive.  Just make sure you give them G12 coolant/water and make sure they don't use anything else.  Do not use dishwashing soap or regular simple green cleaner because these will foam or corrode aluminum.

To refill coolant:

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 VW coolant!  It will turn brown and sludge.  Make sure you mix the coolant in a ratio of between 40-50% water and the rest of the solution coolant.

Put back and secure any hoses or drains that you loosened earlier.  As you add coolant/water to the coolant reservoir, air will slowly come out of the bleed hose that returns to the reservoir at the top of the tank.  During this stage, the engine should not be running.  You can also Unclamp the hose outlined in yellow and with arrows 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 and I just use this hose because it's very 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.

Once the system is full, start the engine, and it will purge out any remaining air.   Leaving the heater on hot won't get the coolant out of the heater core since it's always running through.  Make sure any hoses or drains that you loosened earlier are secure.  

Why not just add coolant into the reservoir on an empty coolant system, start the engine, and let it pump itself to gradually bleed out the air?  Because that would take longer and the water pump would be starting on a dry system.  During start, 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, so maintaining proper level of coolant prevents water pump failure, amongst other nasty problems.

Recheck that the radiator drain and all clamps have been retightened.  Check the coolant level.

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 could spray out so be very careful opening the coolant system while it's hot and pressurized!

Check for any leaks and check the level after a longer normal drive.

Are there broken pictures or do you have more questions on how to flush the coolant system on a 2005.5-2006 Jetta TDI engine?  Please post in the forums