www.taligentx.com - Collections     Tuesday, July 22, 2014

Coolant Flush

The cooling system needs to be flushed every now and then to prevent corrosion in the engine and radiator. While ethylene glycol doesn't break down, the additives used to keep water from attacking and corroding metal will wear down. The organic acid additive coolant used by VW should be good for ~5 years/150,000 miles.

In my case, I flushed the system to switch from G12 to Prestone Extended Life - more info here.

Part Information & Sources:

Volkswagen G12 coolant - ~$20/gallon
Prestone Extended Life coolant - ~$8/gallon
Distilled water (preferably reverse-osmosis/deionized water) - 3 gallons

Tools Needed:

  • 19mm socket
  • Torque wrench

Draining coolant:

  1. Start by propping up the car on ramps or jack stands.
  2. Get under the car and remove the noise insulation panel (belly pan).
  3. Remove the driver side bumper panel to get access to the radiator drain (it just pops out). If there is a flexible piece of plastic in the way, move it aside to access the drain valve. (illustration)
  4. Remove the coolant tank cap.
  5. Attach a hose to the radiator drain leading to a collection container. Open the drain valve, allow to drain, and close the valve. (illustration)
  6. Once the radiator is drained, it's time to drain the engine block. Look under the car and find the water pump drain plug - it's a large 19mm bolt. Open up the bolt, and have a container ready to catch the draining coolant. Clean off the bolt, reinstall and tighten to 22 ft-lbs/30 N-m. (illustration)

Flushing the system:

  1. The cooling system needs to be bled while refilling to get air out of the coolant passages. Look for two rubber hoses covered by a black plastic sheath to the right of the battery. Pull down the sheath (it's rather annoying to work with) and the hoses should be exposed. Unclamp the left hose with the white mark surrounding a hole in the hose. Pull the hose off the connector until the hole is exposed. (illustration)
  2. Unscrew the coolant tank and set it as upright as possible - this sets the coolant level above the hose bleeding level. (illustration)
  3. Set the interior temperature control to maximum heat - this allows coolant to flow through the heater core.
  4. Fill the system with water until the bleed hole begins to seep.
  5. Push the bleed hose back onto the connector, close the coolant tank cap, and start the engine.
  6. Let the engine run for a few minutes until the lower coolant hose becomes hot (until the thermostat opens), and then let it run for a few more minutes. You can speed this up by running the engine at 1800-2200 rpm.
  7. Shut down the engine. You'll need to wait a while (up to an hour or two) for the engine to cool down before you can drain and refill the system. The issue here is that draining the coolant soon after shutting down the engine leaves the engine hot. If the system is refilled with fresh cold coolant, there is a large temperature differential and the block may warp or crack. It's unlikely, but possible. Waiting a few hours for the engine to cool down is one way to get around this. The other is to simply heat up the replacement coolant before adding it to the system - I'm impatient, so this is what I usually do.
  8. This cycle can be repeated as much as you'd like - if the old coolant was clean and free of contamination, I just flush with water once. If I'm working on an old car that has scale and gunk in the cooling system, I flush until the water leaving the system is as pure as when it went in.

Refilling the system:

  1. Drain the system as before.
  2. Mix up a batch of coolant - use a 1:1 mix ratio of water and coolant. Note that you may need to have a bit more coolant in the mix to compensate for the water that remains in the engine block (even after opening up the radiator and water pump drains).
  3. Pull out the bleeder hose and refill the system until coolant seeps out.
  4. Reseat the bleeder hose, clamp it, and replace the plastic sheath.
  5. Recap the coolant tank and reinstall it.
  6. Run the engine until the lower coolant hose is hot again. The coolant level can drop a bit as air is bled out of the system. Add coolant until it's at the high mark on the tank if needed.

Done! Check for leaks, then go for a drive...

Comments:

  • Wow! Thank you so much! I am no longer a Mechanic, but I was (25 years ago). I would not have been able to perform the coolant flush and thermostat replacement without your post! Oh, BTW, the "Stant" thermostat did not work at all..due to poor fit, it leaked (heavily). We purchased a VW thermostat (quite pricy at 35 $) which worked perfectly! Also, I had never heard of "G 12".... we used "G 12". Just want everything to run smoothly, literally and figuratively!
    Patrick Zadd Norfolk, Virginia USA - Feb 21, 2013 @ 5:50 am
  • Found deviations when flushing a 2003 passat 1.8T manual B5.5 AWM engine. It has no exposed water pump with drain plug. Had to use red plastic drain on radiator front via removed grille panel to drain same. Thermostate/housing is at mid-height on drivers-side of engine block, behind alternater. When thermostat is cold/closed, had to fill block thru heater hose. Even so, only got 5.5 gallons into system instead of reported 7.4 gallon capacity. Will have to test coolant to varify adequate protection. Otherwise, at 106K miles, old G12 coolant was clean and clear with no sediment in system. Installed Prestone Extended 5 year/150K collant.
    Dan Brown - Oct 24, 2012 @ 11:29 pm
  • Do you mean flushing the steysm?Bleeding the steysm is removing the air, and there is a bleeder screw located near the thermostat to release the air. You also have to squeeze the hoses, esp. the upper radiator hose to release trapped air.Flushing the steysm is pretty simple too, the manual will give good directions on that. There is a drain bolt on the block, located somwhere near the exhaust manifold, and I remember having a hard time getting the bolt off because my wrench kept almost hitting the radiator. I haven't flushed the steysm in a couple years.
    Andreia - Aug 25, 2012 @ 7:47 pm
  • My 2004 has only 35000 miles but it has leaked out the radiator coolant. Can anyone help on how to replace the hoses?
    Guls (USA) - Feb 16, 2012 @ 10:15 pm
  • Thanks all for your help in saving me a bunch of money on my 2001 Passat with heater issues. VW dealer wanted $1,700 to replace core. I followed your instructions to flush heater core and issue resolved. BTW - heater hose is 3/4". After completed, I did take to dealer for flush (because jiffylube not allowed access to G12). Thanks again!
    Ted T - Dec 29, 2011 @ 7:05 am
  • I just changed thermostat flushed system and changed coolant following your excellent instructions and photo's. It made the process easy, this is the best site I have ever come across. Thank you and best regards.
    Lenny England UK - Oct 22, 2011 @ 1:46 pm
  • I've been having problems with the oil coolant Passat tdi 2005 (replaced twice) and problem persists. The light pops up stating go to emissions garage, stop! I have had it flushed on both occassionsbut still have to tap the collant up with water. What are the likely underlying problems causing this or adding to it?
    Would appreciate tour advice and counsel?

    Anraoi
    Anraoi, Ireland - Aug 7, 2011 @ 5:23 pm
  • I just acquired a 2004 Passat Wagon V6 and I would like to know if i can get the Wolks Wagon preffered Coolant at watmalrt store. if you know please share.

    regards
    Janes
    Sean San jose, CA - Aug 1, 2011 @ 7:49 pm
  • Hi, nice site, i have a question, i took my passat to the mechanic, its same like yours, the problem is that the expansion tank in the back has a third tube and the mechanic doesnt know to where is connected, so the car is loosing water but not by a leak! its just pure steem, can you tell me or take a picture to where is it connected? thanks a lot!
    Mario, Guatemala - May 14, 2011 @ 3:28 pm
  • I have a 2003 Passat wagon 1.8T and I have been unable to locate the coolant temperature sensor on my car. I have a code (cel) P2181 "cooling system malfunction" and P3041 "engine termperature sensor". I thought I would start with the least expensive and most probable problem solution and replace this part. Locating this has turned out to be quite a problem?
    Thanks,
    Rudy (USA California) - Apr 9, 2011 @ 4:27 pm
  • I have a 2003 1.8L Passat without reaching normal operating temperature of 190 in January. Head gasket, timing belt, T-Stat and H2O pump replaced in October. Once Nov. came seen temp gauge not reaching 190. Check engine lite on with a P2108(??) not sure of the number but meant engine coolant performance error. Figured air in system. Bled and still no normal temperature. Upper radiator hose hot lower cold. Decided to go after the T-stat as it was from Murray's. When I realized T-stat was never replaced by the friend mechanic. ha on me. Once the OEM T-Stat was installed. Bled the system but never had a good flowing stream out of the core hose. Why??????????????? Let the car warmup. Took 10 min. to reach 190F. Heat blows hot as can be. Should I realize there is no air in the system??????????????
    DG ZEP - Jan 14, 2011 @ 4:37 pm
  • I would like to know what type of oil filters you use in your vehicle.. Reason is I\'m looking for an oil filter:
    -OX 162 made in austria
    - non metalic filter, it is a cartridge like filter
    - diamter 1 3/4\"
    - length 2\" 3/4
    - center hole 3/4\"
    - o ring 2 3/8 X 1/8
    Would you have such a filter? and what would be the cost.. ?

    Hope to hear from you asap, been looking for this for over a week now.
    thank you
    J.P.

    J.P. Coudriau, Canada - Nov 16, 2010 @ 7:32 am
  • Thanks for this awesome tutorial! My g/f's 2000 1.8t had no heat or it would work intermittently after long drives. I think her problem was more along the lines of her reservoir being low on coolant. It was so gunked with scale it looked like it had plenty in it so I never added any. The cap broke apart when I opened it because it was corroded together. I had to pry the gasket out with a flat head screwdriver. I'll need to order a new one of those.

    Her system had a LOT of rust build up. I drained the system and hooked up a garden hose to the heater core and flushed it from both directions with full pressure. Her coolant looked mud brown and absolutely disgusting. Then I opened the water pump drain and let that flush for quite a while. I opened the radiator drain and let it flush for a while. Unfortunately, it keep clogging up with rust scale. I unhooked the lower reservoir hose and it was cake inside with scale. When I squeezed the hose I could hear it crunching inside. I pointed it to the bottom of the car and turned the water on. It drained slow until all of a sudden the scale broke up and shot out of the hose like a bullet. I can't believe how much there was.

    I just ran some Prestone cooling system flush through it for 10 minutes after full warm up and it is cooling down right now. Her heat gets warm right away and as the car warms up so does the heat. Temp stays right at 190 so at least I didn't jam the thermostat with crud yet.

    Hopefully, this resolves the problem or else I'm going to have to keep flushing her heater core every other week.
    Chris H USA - Oct 16, 2010 @ 8:45 pm
  • ...just want to say thanks to all who posted info . I have 04 passat glx w/ 6cyl 2.8 and like some of you do not have heat for last year . I had flushed @ oil shop but did not fix problem . I did have a bunch of crud that based on you reports was probably caused by adding two types of fluid instead of staright dexcool . Heat core replace is $$1250 @ dealer so I decided to go it on my own . Frst I removed in & out hoses to heater core . I took two hoses , one with H2o adapter on one end and the other just plain hose , and fit them in heter core in & out . I flusshed with water for a few then I would unhook water from hose and blow air from compressor thru until nothing comes out . I did this several times and on occasion I would switch directions . I blew and flushed all in a bucket and alot of crud came out . Day two I stopped by store and picked up CLR , a cleaner from grocery store for lime , rust and calcium , and I drained the core of all water and added this and let set for 1hr or so . When I blew it back out I removed even more crud . Then I did as instructed and removed fluid from radiator and flused for 1 hr or so . On occasion the drain was running slow so I shot it with a little air and the flow would pick back up . I never was able to locate water pump drain but nonetheless when I was finished and refilled the radiator and hooked back up , I had heat ! I bleed the air out per your instruction and made sure to lift the reservoir higher than core hoses . Thank you to webmaster and to all who took time to post . Total cost to rejuvinate heat was around $25 dollars and 2 eves in the garage having fun with my 13 yr old son . Thanks again , Mickey
    mickey - May 16, 2010 @ 12:48 pm
  • After an oil leak into the coolant, the shop flushed the engine several times. I still get globs of brown oily globules in the refill canister. Should the engine be flushed again and/or when will this stuff ever go away? Or will it? Also is this harmful to the engine short- or long-term?
    Marque - Mar 29, 2010 @ 9:21 am
  • where is the water pump drain bolt on 1.8t (awm) motor? did not find one in lacation suggested.
    daz69 - Mar 11, 2010 @ 6:47 pm
  • OK Please help!? I have a 2001 1.8t I changed the timing belt water pump thermastat and flushed the system. But my heat is still not fully hot. Its warm the thermastat gauge goes from 190 back down once in a while. if i turn the heat off and then drive it for a few minutes the heat comes out strong then goes to warm again. What could the problem be please help. Email me at Johnudamiani@aol.com if you have the answer
    Johnny - Feb 17, 2010 @ 2:23 pm
  • This is a great site. However, I can\'t find the water pump drain plug for Passat TDI (B5.5/BGW). Anyone knows where it is? Appreciate any help.
    subest - Jan 12, 2010 @ 2:18 pm
  • I just did my head gasket on a 2001 passat 1.8 turbo Took me four weeks to do it but i got it done. I and a friend used the HAYNES MANUAL from Auto Zone... replaced the thermostat. Should have checked the water pump when I pulled the Head and the thermostat. Car started to over heat. repulled the thermo and checked the water pump by placing my finger inside the thermo housing and finding the impeller of the thermo. It rotated freely with the timging belt still on the car. Had to break down the timing assembly and replace the thermo. MKAESURE YOU HAVE TDC AND YOU REALIGN YOUR TIME MARKS OTHERWISE S.O.L. NEW ENGINE!!!! After all said and done, Still no heat. see previous comment about flushing system. You can pull the hoses and flush with the engine hot to get the air trap out. just make sure you add enuf coolant for the winter months. I flushhed the system to get rid of any contaminants and old antifreeze (G12) refilled with Prestone 1:1 Make sure that you change the oil and rechange after 500 miles to flush out any gunk that might have gotten into the engine. You Might get a low oil pressure Over 2000 RPM. But An oil change solves this problem. With all that said I hope this helps the backyard Mechs.... By the Way We did this without taking the Front end off and the battery connected the entire time. Had to remove passenger headlight to access the tenssioner. Hope you all have small hands and alot of patience. GOOD LUCK TO YOU ALL
    Chris Cincinnati Ohio - Oct 28, 2009 @ 6:41 pm
  • For those of you that have changed your water pump,and have lost Heat Try this per the haynes manual. Take off both heater hoses connected to your heater core and flush out both sides of the hoses with a garden hose at normal water pressure and the heater core it will get rid of the deposits in the core and release any large air traps in the system. Reatach both hoses and bleed system as normal through the weep hole. Any remaining air will be taken out by the cooling system.
    Chris Cincinnati Ohio - Oct 28, 2009 @ 6:25 pm
  • here was my problem by the way this is my sons car he bought the car when it was still warm out nowits cold and no heat everything else works. so he brings his 2002 passat 2.8 to a vw dealer and they tell him it\'s the heater core and it will be $1400 so now I look at it I could not find were the hoses until i found this site so now i remove both hoses and put a garden hose to the core water flows thru easily not the core that dealer wanted to replace. reconnected the hoses still no heat at this point i don\'t know if there is coolant flow so i connect a clear hose between the in and out hoses that go to the core and no flow untill the engin was reved then i followed the bleeder instuction and now there is heat as long as the car is under load our next thing to try is the thermostat this site was very informative and helpfull (getting warmer)!!!!
    joe usa - Oct 21, 2009 @ 4:53 pm

  • joe maneca us - Oct 20, 2009 @ 6:41 pm
  • can anyone give tips on changing the theromstate of a 2002 passat (1.8 turbo)
    dbush - Aug 2, 2009 @ 12:51 pm
  • Your website is very helpful, thanks for documenting all your repairs so well. I own a Bentley manual and, for the life of me, still couldn\'t find the infernal bleed hose. Then I see the pic on your site and it\'s all so clear now. Silly me.


    Nate - Jun 22, 2009 @ 2:26 am
  • I\'m glad I found this website as it helped me a great deal. I had to replace the radiator on my 1999 1.8 20V as it had corroded and leaked. However, I found this site particularly helpful with the flushing of the remainder of the system and the refilling procedure. My drain valve was different however; I was looking for the purple knurled knob but I had a black \"tap-like\" thing instead.
    Thanks very much for publishing this. 8-)
    Adrian, Bristol, UK - Feb 28, 2009 @ 2:52 pm
  • dave usa if you have questions goto passatworld.com click on b5 forum the people there know pretty much everything and are very helpfull.
    bob,usa - Dec 21, 2008 @ 10:12 am
  • The dealership wanted to charge me $800 to replace the coolant thermostat and do a flush fill. I decided to do it myself, got the thermostat, G12 coolant, and a Bentley DVD Service Manual. Looked over the physical location of everything today, rmoved the belly pan, and figured I\'d just take off the lower hose to drain. Problem is it\'s hard to reach and I\'m afraid I\'ll break something pulling it off. There was a metal locking bracket i got off easy enough, but I was sure if it just pulls off with some effort or there\'s some sort of threading? It\'s a 2001 Passat GLS 1.8T I\'m trying to avoid removing the front bumper to get to the drain plug. (nice design VW)
    thanks and regards,
    Dave
    Dave USA - Dec 13, 2008 @ 5:09 pm
  • My passat blows cold air when the heat control is on hot, There is flow coming in and out of heater core, Temp gage is working fine also, Car is not over heating either, Please someone let me know Anything that I might try Thanks
    John Ohio, USA - Oct 21, 2008 @ 7:37 am
  • i fix my heater.. i follow these step like 3 time and it didnt work. my heater core was clogged, i disconnected both of the bleed hole the goes in and out the heater core as shown in the pic above and water pressure both holes 5 min each non stop and connected anything and ran it with water instend of antifrezze in the mean while and it work.. ppl with heater problems should try this!
    gus - Oct 20, 2008 @ 1:04 pm
  • maybe your coolant got like mud beacause you put the wrong antifreeze, your suppose to use the orange kind like GM vehicles DexCool you can buy that at autozone
    usa beaner - Oct 6, 2008 @ 9:45 am
  • I had a 2002 Passat 1.8T, recently I had my Coolant check, and I was told that the coolant dirty and like mud. I\'d as the Dealer how did this happen, I got my answer I DON\'T KNOW... Any Idea guy\'s how did this happen? thank.
    By the way I only got 108K.
    Rolando (CANADA) - Jul 18, 2008 @ 7:10 am
  • 2003 Passat 1.8 T. Flush went well and followed procedure step by step. Problem: Interior heating system no longer blows heated air. Any help out there?
    Ron
    Ron Concord MA - Jun 30, 2008 @ 1:44 pm
  • my car doesnt work
    ivan - Jun 19, 2008 @ 10:03 am
  • my car doesnt work
    ivan pilsen - Jun 19, 2008 @ 10:03 am
  • Valuable site. Glad I stumbled across it. Should help with my Passat lack of heating following t\'stat cx. Thanks all
    Steve (UK) - Mar 11, 2008 @ 2:39 pm
  • I had a coolant drain and fill done at a local oil change(mistake) place on my 2002 Passat 2.8 4motion. I now have no heat, I followed your procedures for refilling and bleeding, till coolant seeped out of bleed hole. Still no heat, any suggestions? I had nuclear heat until this drain and fill. Thanks
    Mike USA - Dec 1, 2007 @ 10:22 am
  • Chris USA: Leave your personal comments to yourself. G12 is far more trouble than it\'s worth. You obviously don\'t know what you\'re talking about.
    Don USA - Oct 14, 2007 @ 9:37 am
  • My Oil Cooler just failed on my 2000 Passat, 7 years and 79,000 miles. As a result that mixed Oil with Coolant and I have a big mess to clean up. I got the crankcase clean of radiator fluid, this site has been a great help in getting the gunk out of the cooling system, many thanks for the detail and pictures, better than my Haynes repair book.
    Mark K, USA - Sep 12, 2007 @ 2:36 pm
  • The fact that you advocate switching away from G12 makes this site a worthless pile. Good Luck with sub par cooling.
    Chris USA - Jul 25, 2007 @ 10:43 am
  • I have 2000 Passat need to know where the thermostat is located please help
    bone - Jun 5, 2007 @ 8:15 pm
  • Thanks for the great write-ups; they\'ve been very helpful.

    My \'02 Passat (1.8T, AWM) has been overheating lately. I replaced the temp. sensor, the expansion tank/cap, thermostat, and now finally the water pump. After the latter, I thought I finally fixed it because I was able to drive longer than I had earlier w/o the temp gauge budging beyond normal (190 degs). But then today it went up and started boiling again. I think I was just lucky yesterday because I had also replaced all the coolant w/ brand new stuff.

    So what could the problem be at this point?
    Mark - May 19, 2007 @ 4:32 pm
  • Where do I begin? First, it would be great to see your reply\'s to the questions posted in the comments field. Second, do you know of a manual for a 93 Passat GLX? I\'ve looked almost everywhere. And third, the reason for which I came across your site, I can\'t find the drain for the radiator on my 93 Passat GLX Wagon.
    Eric (Montana) - Apr 25, 2006 @ 3:26 pm
  • i have replaced the thermostat and flushed the system but the thermostat doesn`t seem to be opening,the bottom hose never heats up.can you suggest why?PLEASE
    britny,usa - Sep 26, 2005 @ 8:30 pm
  • thank you i found my thermostat,it seems like it is not opening,what would cause that
    britny,usa - Sep 25, 2005 @ 3:02 pm
  • i have a 2000 passat that needs a new thermostat and i am new to this car can you tell where to locate it?please
    britny,usa - Sep 25, 2005 @ 1:08 pm
  • Hi,

    great site, thanks.

    The Owner\'s manual for my 2001 Passat says the the coolant system is sealed and the
    coolant does not need to be replaced. So why flush it?

    Thanks,
    Gajanan
    Gajanan Joshi - Apr 21, 2005 @ 1:29 pm
  • will this work on a 1993 passat as well?
    chris - Mar 29, 2005 @ 7:22 pm
  • Thanks for the writeup!
    slofizz - Feb 27, 2005 @ 10:50 am
  • I found loosening the hose going onto the water pipe easier than locating and undoing the bleed hole. Note: The bleed hole arrangement on my radiator (new @ 2004) was different to the illustration.
    Ken - Feb 19, 2005 @ 9:14 am
  • This may be an obvious question...but to refill the system for the flush and final fill. Do you do this through the recovery tank?
    Kassel - Feb 13, 2005 @ 7:46 pm
  • To ensure at least 50/50 mix regardless of water left over from flushing I add to first 50%-60% of the stated cooling system capacity in pure undiluted coolant, then add water to complete the fill.
    J - Jan 5, 2005 @ 9:47 pm
  • I now have come across your reasons. My apologies.
    - Jan 5, 2005 @ 8:31 pm
  • Other than cost, what led you to change from the G12? I know if the two get mixed (avoided by a complete flush) clumping and just big problems supposedly occur. What conclusion did you come to in order to assure yourself the change over was proper?

    Thanks for the site too. Always a great help.

    98 AEB B5 1.8T Manual Variant
    Stephen - Jan 5, 2005 @ 8:22 pm

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