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coolant flush DIY: mk3 Passat and Jetta TDI
Engine coolant flush for 1996, 1997 Passat and 1997, 1998, 1999 VW Jetta TDI
Difficulty 2/5Back to mk3 "how to" index and FAQFor the 1998-2005 Jetta, Golf, New Beetle, see 1000q: mk4 coolant flush
This DIY article shows how to flush the coolant or just drain it on a VW TDI engine.
Engine coolant is the same as engine antifreeze. 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 some coolant is lost during a water pump change, you'll end up draining a lot of it every 60,000 or 120,000 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.
The original fill on the passat was blue g11 coolant and is not compatible with any modern VW coolant. G11 was not a lifetime fill and should be flushed thoroughly out.
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 (not app. to 1996 passat TDI only), 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. See 1000q: oil cooler and seal replacement. 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 passage but 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 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.
Coolant capacity: 6.5 Liters of coolant/distilled water
Ratio: anywhere between 60% coolant/40% distilled water and 50% coolant/50% distilled water, 60% coolant gives better freezing protection
Coolant type: VW G-012-A8F-M1 (ZVW 237 G12) or Pentosin G12 (pink color) 1.5L G12 coolant from kermatdi
and/or (pink and purple are compatible) VW G-012-A8F-A4 or Pentosin g12+ (G12 plus, purple color)
Enough coolant and distilled water to satisfy the required 6.5 liters total capacity. 3 liters of G12 concentrate is enough for a normal flush since there will be a little left over in the system. Otherwise get an extra 1.5L or gallon of coolant.
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.
hose clamp pliers, they can fit into a tight spot and lock the clamp open
Draining the coolant
If the hose clamps for the hoses you want to remove are accessible without raising the car, just securely park the car. If the hose clamps are in odd locations that require you to get under the car, 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 engine top plastic cover.
Since some model years are slightly different, you can modify this to suit your car. 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 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 or vice versa, see the below section on thoroughly flushing the coolant system.
Your radiator may not have a drain valve so remove the return radiator hose. Open the coolant reservoir cover (first picture) and place a catch pan below the lower radiator hose. This car had a small oil leak in the past which discolored the coolant reservoir. They are cheap so if you can't see the coolant level, just buy a new one. Yours will probably be a little yellowed from age.
The radiator has a hose at the top which is shown below and a hose at the bottom (second picture). To remove hoses, don't yank on the hose or pry with a screwdriver. Try using pliers to twist the hose and break the seal first, then it will pull off much easier. Remove the hoses at the radiator and the oil cooler (circled red below) to drain the coolant. You can really use any hose, but these hoses are more accessible from the top and are low enough to let most of the coolant drain out. If you need to thoroughly flush the system, see the section below.
Thoroughly flushing the coolant system of gunk
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 and skip the section below.
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 do not to use anything else.
First press a garden hose against the removed oil cooler hose and it will backflush most of the old coolant out. Remember, first twist the coolant 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. New and clean coolant reservoir tank pictured.
Also remove one of the heater core hoses on the firewall and push the garden hose against the openings to flush out the heater core. Don't stick a power washer up there but a gentle garden hose flush won't damage anything.
Also remove the coolant flange on the driver's side cylinder head 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.
If you can't find a dump for used coolant/antifreeze, engine oil, gear oil, or other car fluids, earth911.com can search for a local waste disposal.
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. Do not 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. If your car still has blue coolant, I suggest a flush and refill with G12.
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 connects to the reservoir at the top of the tank. During this stage, the engine should not be running. 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 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.
Once it is full, start the engine, and it should 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 the core. Let the engine cool down and drain.
Recheck that the radiator drain and all clamps and hoses 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.