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Coolant flush and bleeding - VW Passat TDI B5
VW Passat TDI coolant antifreeze flush and change
back to 1000q: B5.5 VW Passat TDI "how to" index
Engine coolant is the same as engine antifreeze. This article shows how to change it on your Passat or Audi A4, A6.
Although VW says it's a "lifetime" fill, a reasonable suggested change interval is about 100,000 miles or as needed, depending on use. Since a lot of coolant is lost during a water pump change, you'll end up draining a lot of it every 100,000 miles with the timing belt service. Remove the lower radiator hose too and what's replaced will be enough to keep the coolant in good condition. Many high mileage cars show clean coolant passages with G12 even after 200,000+ miles! Your coolant should be pink or light purple in color. Pictured below is the coolant reservoir. Note - I found that my coolant tank had a hairline crack so it lost a little bit of coolant over time as evidenced by the white stains below the coolant tank.
Warning: do not mix red, pink, or purple VW G12 coolant with green or blue coolant or other non-VW/Audi OEM or OEM compatible coolant! 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. Just tell your vendor that you need G12 coolant because they are all compatible.
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.
Do not use radiator stop leak products. Although your VW TDI turbo is oil cooled and not water cooled, stop leak products can clog the turbo water coolant lines and possibly cause damage.
Do not drain your used car antifreeze onto the ground or into the sewer! If you can't find a disposal for used coolant, earth911.com has a search for your local waste drop off.
Parts for coolant flush
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)
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
Procedure - first drain the coolant
Make sure the car is safe and secure before doing anything else. It's best to flush a lukewarm engine. If the engine is too hot then a cold flush could crank the engine because of the sudden temperature change. Remove the engine top plastic cover (3x 10mm nuts)
The idea is that you want to open a low spot to let the coolant out and refill as necessary. If your fluid is still pink/red/purple and clean, you can just open the lower radiator drain and the oil cooler hoseand 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.
You may have to pull out the driver's side lower grille to get access to the drain. Press on the clamps circled.
Put a hose on the radiator drain to catch the coolant. (bumper removed for illustration) Open the coolant reservoir cover and place the hose into a catch pan. Use a phillips screwdriver to open the drain - the drain is plastic so be careful.
You can apply low pressure air to the overflow coolant tank hose (yellow rectangle) to get additional fluid out. To easily remove seized coolant hoses, don't yank on the hose or pry with a screwdriver. Use pliers to twist/rotate the hose end to break the seal first. This will make it much easier to pull off. This drains coolant out of the radiator and coolant overflow tank. You can also pour some distilled water into the upper radiator hose (yellow rectangle) to get clean out any stuff in there.
To drain the coolant out of the engine block, remove the 2 oil cooler hoses (one shown with red arrow below). (some items removed for illustration) You will need to use the remotely operated spring clamp pliers. Again, rotate the hose first before pulling it off. If you need to thoroughly flush the system, see the section below.
Thoroughly flushing the coolant system
If you want a through flush, leave the lower hoses open and apply low pressure compressed air to the coolant reservoir hoses to push the coolant out. Use your finger to block the other end of the hose to effectively push air out the open hose. 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. Skip the paragraphs below and go to To refill coolant.
If your coolant is contaminated you need to flush a few times with water first, then radiator flush/water, then water, then distilled water during the final flush. 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 do not to use anything else.
First flush the heater core. Remove both hoses pictured below (red arrow is for a later step, bleeding the coolant system). Attach a drain hose to one of the hoses and press a garden hose against the other. Once it's clean, flush it with distilled water.
Then remove the oil cooler hose pictured above and flush it the same way as the heater core. Remember, first twist the hoses at the flange to break the seal first. This will let you pull it off much easier. Remove the hose at the coolant reservoir and flush at the hose there. Also remove the upper radiator hose and flush there.
There will still be some old coolant lingering in the system so repeat a few times and then on the last flush, use distilled water. If you need to clean oil out, try radiator flush cleaners. 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 40-45% water and the rest of the solution coolant.
Remove the upper radiator hose and fill as much coolant/distilled water as you can.
Put back and secure any hoses or drains that you loosened earlier. Double check all the hose spring clamps or clips. As you add coolant/water to the coolant reservoir, air will slowly come out of the bleed hose on the reservoir and the heater core. During this stage, the engine should not be running. 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.
Bleeding coolant system reservoir in a Passat or Audi A4/A6
Slide the passenger side heater core coolant hose 3/4 way off. You want the highlighted hole (red arrow in earlier pic of the heater core hoses) to be exposed beyond the plastic flange.
Once the coolant tank is full and isn't going down in level, raise the coolant reservoir above the level of the heater core bleed hose. Keep the reservoir raised and full until coolant comes out of the heater core. The bleed hole is at the top of the hose so any air comes out of the hole and you can see a few sprinkles coming out of the hole in the above pic.
Do this with the engine running at first. Once the engine is warmed up and any air bubbles have come to the heater core, you can do this with the engine stopped. Leaving the heater on hot won't get the coolant out of the heater core since it's always running through. 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!
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, drive around and then do it tomorrow. Any bubbles will make a gurgling sound behind the dashboard. The next day, most of the air will be in the heater core or will have already come out. Repeat the bleeding procedure and top off the coolant.