VW Jetta Coolant Leak Repair

This is a fastener-by-fastener description of how I diagnosed and repaired a slow coolant leak as a result of a bad coolant hose flange on a 2001 VW MKIV Jetta Sedan with automatic trans and 2.0L (AEG) engine. This is a known issue with VW engines including the MKIV, and it is the most common cause of a slow coolant leak for this vintage engine.
Note that the coolant used in many VW engines is G12, only available through the dealer. Literature published by VW explains that G12 is not compatible with other coolants, including universal coolant sold elsewhere. They warn that mixing G12 with other coolants might cause engine or seal or sensor damage, and that their warranty may be void if there is evidence of coolant mixing and damage resulting from that.
There is another useful description of how this repair is done at the following link done by MikeWire on the VW Vortex forum.
forums.vwvortex.com/showthread...
This video is posted for entertainment purposes, and is not an instructional guide. Do not attempt this at home without professional advice. I am not a professional mechanic, and any misadventure resulting from your attempt to repair your vehicle is your responsibility.

[@cyn1calsphere]

You sir are incredible at making DIY vehicle repair tutorials. This was incredibly useful and full of great tips for an amateur mechanic like myself!

[@spelunkerd]

Thanks so much for the kind words!

[@hcoalex18]

Thank you, my Jetta was leaking all over the garage and I couldn't figure it out. I thought that it was the water pump, but after watching this video I can see that it was the coolant flange. Thanks for the help, saved me almost 300 dollars =)

[@marcelpouslan7652]

NOW THAT is how you make a contribution to the digital domain. Professional, high quality, articulate and with step-by-step clear and concise visual guidance to avoid any issue whatsoever with the reinstall repair of this particular component. I am actually about to head out to the driveway and replace the gasket on my flange. I will be using copper RTV however. After owning a 1989 Jeep Wrangler since I was 15 (first car and still have her) I have learned ALL fluid mating surfaces get RTV. Period. Thanks again. This really saved me some serious money

[@spelunkerd]

Thanks for the feedback, Marcel. Good luck!

[@desicrater2191]

This video was incredibly helpful. I skipped the dye procedure because coolant was practically pouring out of my coolant flange. I bought an OEM coolant flange and coolant temp sensor as replacements. Installation was a breeze. My temp gauge is reading again. Thanks for taking the time to upload.

[@spelunkerd]

Yeah, I'm sure dealers don't use the dye since this leak is so common with this vehicle, and you get pretty good evidence from closer inspection. I'm glad the vid helped, thanks for the feedback!

[@spelunkerd]

Thanks for coming back to record your experience and to offer more practical advice. Guys like you make the thread that much more valuable.

[@chumanilakota]

You're a very caring mechanic. I was watching how you carefully removed and set aside other parts to the car. Thank you for becoming a great mechanic...its not many of you out here.

[@leagueofinternationalmenof1108]

Excellent video. Had considered making one myself as I went about fixing a coolant leak on my mk4 Jetta vr6 (essentially same layout), but yours was so well done I decided to not bother and just used this as a reference while I did my own repair. I appreciated you taking the time to clearly show all the connectors and how to remove them. Just so you know someone noticed!

[@spelunkerd]

Thanks, man!

[@Gundaaaaa22_____]

​@@spelunkerd uh qwq

[@hangalen]

I watched your video before repairing our '02 Jetta GLS 2.0 Liter (AZG) Wagon. We never identified an obvious flaw in the coolant flange or gasket but seems to have stopped the leak. Thanks so much for posting this, it was a great help. We spent some time carefully cleaning up the area so the gasket sealed properly. It took a little more than a gallon but not 5 liters. We did pull the hose at the oil filter to drain most of the fluid. We also ran car w the reservoir open, no obvious burps.

[@spelunkerd]

Thanks for the update, Zsolt. I'm not surprised a different model required different access, and I'm sure future viewers will appreciate your input. Evidently your problem was not with the coolant hose flange but a different port. It does highlight the fact that every repair is different, and a standard approach only takes one so far. If only auto makes would quit using plastic parts in areas subjected to huge temperature swings. It's great to talk with you again. Dave

[@skittlesstarburst4532]

I have an 04 and had a small leak... now it’s a bigger leak and leaking and steaming off that same general area.. thanks for the video. I’m glad it’s not the radiator and I was less than 5 miles from home... sat around for a few minutes and made it home... it’s always gotta when you get that job starting the next day...

[@tylermitchell349]

I just wanted to say thank you. The time you took to make this video is much appreciated.

[@spelunkerd]

You're welcome, thanks for the followup.

[@spelunkerd]

Your compliment today was more than enough. Thank you back!

[@paramonkey7]

Completed this identical repair on a 2001 Golf GLS 1.8L T this morning and thanks to the details learned from this video all went well. I approached disassembly a little different than in the video. I choose to take the air box and associated tubing out to gain better access from the bellow. This also aided in diagnosing with just a mirror and lighting. After access I found a length wise 1 inch heat stress crack on the rear main port. Total cost of repair $12.35 CAD & 1hour labor. Thanks

[@Mancat57]

Your extra time on the clips and hoses is a really great part of this overall great video, thanks.

[@PeterDavoust]

Great video, I appreciate that you took the time to make it. My Jetta has a coolant leak that I'm planning to repair myself, and this was a great start to my research. Thanks!

[@spelunkerd]

+Peter Davoust It's a pretty simple repair if you pay attention to where everything goes and reassemble carefully. Don't forget to burp afterward since it's common to overheat because of inadequate burping. Read through the comments others have made. If there's going to be a delay, be sure to keep that coolant reservoir AND the radiator topped up since a secondary overheat could kill your engine very quickly. Good luck!

[@michaelgabriel7919]

Spelunkerd. Thanks! I recently bought a 200 Jetta 2.0 that has a slow coolant leak. The previous owner said it was a hose, but I was wary. I intend to get the dye you used and check it out asap. Thanks for the step by step, I have done car repairs myself in the past but I am no expert. Your video was informative and a real time and money saver for this DIYer.

[@spelunkerd]

Thanks for the feedback. Guys who work at the dealership say this happens to most vehicles of this model, so hopefully it's an easy fix, as shown. Good luck!

[@audimattro]

Been trying to find a mystery leak on my MK5 Jetta... your video helped point me to the cause. Later generation, different motor (2.5) but still the same exact cause. Wow. Annoying to deal with, but the positive is that I now know exactly what the problem is. Nicely done, thank you.

[@spelunkerd]

Thanks for the feedback!

[@josephhayes7719]

Did the repair tonight! Thank you so so much! A friend and I labeled all the hoses with tape and numbered them. When we put everything back together, we just went backwards numerically.

[@spelunkerd]

Good idea, thanks for the followup.

[@phishphinder23]

2001 2.0 Jetta, Same leak, lower back side of flange was cracked out pretty good. Replaced with new part thanks to vid. All in all 1.5hr job. I kept true to G12 coolant. Came back to say thank you so much for the DIY. Very straightforward and clear. Tips: plastic clips and covers are very brittle, BE CAREFUL! Also, CTS gasket was pretty burned recommend replacing no matter what. New Flange gasket without sealant seems to be holding up just fine. Thanks again!

[@neillellman1915]

Great DIY video, very thorough and easy to understand. I am quite confident in replacing the leaking coolant hose flange on my MK1 Golf by myself. Well done and thanks for this!

[@spelunkerd]

+neill ellman Thanks for the feedback. Good luck!

[@spelunkerd]

I'm glad it helped. Yes, I was a little confused about those two different names until I reviewed an article done on wikipedia explaining all the different models and manufacturing history. Great resource.

[@spelunkerd]

Thanks! Having found very insightful comments from you in the past, I value your thoughts.

[@maxreigert3801]

Thanks for making this video. Extremely helpful. Appreciate your time in making this.

[@nano411]

Thanks a lot. The only problem I really had was the top bolt on the flange, with that metal bar in the way. I had to really pull up on it to get it up out of the way. Couldn't have done it without your video.

[@spelunkerd]

nano411 I'm glad it helped, thanks for the feedback.

[@MightyNib]

This is an excellent video! I especially appreciate the time you took to explain how to disconnect the various flimsy plastic connectors. Thank you!

[@zx8401ztv]

Thank you for your excellent tutorial :-) You have a calmness that makes learning much easyer, and you dont repeat yourself or waffle on for weeks or drift off subject like some people do. EricTheCarGuy is good to watch, if your into tutorials. I dont have a car or drive one and i enjoyed your smashing video :-) Hope the plumbing behaves itself now.

[@stuzman52]

Hey Dave, you just got to love those VW's. To work on anything on these cars, you got to take a pile of stuff off to get to anything. Good video and good detail.

[@spelunkerd]

Thanks Terry. Yeah, with as much maintenance work that was required on old style vehicles, I loved how much room there was in the engine compartment. No more.

[@pyrexpurrvito]

Great video! I like that even with the overwhelming evidence of the source, you confirmed the source with the dye first. Also, I guess I'm not the only one who has wondered why VW chose to use a plastic tube.

[@spelunkerd]

Thanks for the feedback, I'm glad it helped.

[@MuricanMiata]

Thanks boss video paying dividends even in 2023. Friends car gushing couldn’t tell where it was all flowing to the passenger side looking like a water pump until I noticed the puddle on the transmission

[@spelunkerd]

And thank you back! Inadequate burping is by far the commonest (possibly serious) problem when a cooling system is opened. Some engines, like the GM 5.3L, have a coolant bleed hose, but others rely on their mechanics to follow a safe protocol.

[@spelunkerd]

Thank you for the feedback. My experience was similar. I think the rubber gasket becomes less pliant with age, and the low torque spec on those two bolts makes a leak very likely as the engine ages. I think it's a design weakness, and I'm sad that VW seems to have made little effort to offer a fix that would last longer than the original.

[@spelunkerd]

I'm glad it all worked out, Don. There is a lot of pressure in some of the power steering hoses so they need to be tight. Cheers.

[@spelunkerd]

Thanks, Troy. Nice to meet you, and thanks for the sub.

[@spelunkerd]

I'm glad it helped. Thanks for the feedback.

[@spelunkerd]

That's a great point. Whenever I see a plastic flange, I roll my eyes with memories of misadventures that happen indirectly, usually when trying to fix something else. At least you can retap a steel hole, but trying to replace plastic parts can be a more frustrating challenge. Thank you for your comments!

[@batumschrag7555]

Great video. Thank you. Im doing this job on my daughters 02 Jetta in a couple days. Im much less stressed now.

[@garydesantis]

Great help. Considering I have not turned a wrench on any of my cars in 25 years, thus is what I needed. Thank you very much.

[@spelunkerd]

Mechanical skills never die, though fastener designs have evolved. Thanks for watching!

[@alexmiller7723]

I watched this video because my 2002 jetta gls has a coolant leak as well and this video made me feel more comfortable looking at my engine bay. I thought it would be more harder than this to fix it but honestly nothings difficult once you know what you're looking for. THANK YOU SO MUCH MAN!!!!

[@spelunkerd]

+Alex Miller (A Mill) I'm glad it helped, I hope it goes well for you. One word of caution. Stuff happens! Broken bolts, cross threaded nuts, lost parts, forgotten steps, and various other misadventures. Many of those complications happen less frequently to experienced techs using the correct tools, but experience is no guarantee. The best techs are organized and prepared to deal with problems without making things worse or losing control. It can look easy in experienced hands because they proceed in a way that makes it easy. The real test happens when there are unexpected difficulties. So, my message for those who read this is not to be surprised if complications arise. Good luck!

[@alexmiller7723]

+spelunkerd wow thank you so much

[@alexmiller7723]

+spelunkerd I actually ended up replacing the coolant hose flange a few days ago. It was a piece of cake.

[@spelunkerd]

+Alex Miller (A Mill) Great, thanks for recording your experience here.

[@spelunkerd]

It's pretty easy overall. Good luck, and thanks for the feedback!

[@hehlcat]

2021 AND THIS SAVED ME! THANK YOU!

[@pelmeniz]

I have a 2000 1.6L NA Volkswagen Jetta (although it's called Volkswagen Bora over here) and it has the same kind of leak, this video explains everything clearly on what I'll have to do. Thanks.

[@spelunkerd]

What you did to replace the head goes beyond anything I showed here. Nevertheless I'm glad it helped. Cheers!

[@browntroy101]

Loved the great detail in this video! Really good! Thanks!

[@SteveRobReviews]

Well Done !! I had what I first thought was a power steering leak on my truck so I put some die in the system and found leaks all over the place and in spots not even close to the power steering. Well I soon learnt that using a dye and the glasses and uv light that regular coolant has uv dye in it already and it turned out the leak was a bad water pump. Whenever I see a gasket like yours I check to see if it has a specific torque.

[@spelunkerd]

You make some good points, above. Here on the west coast, the temperatures don't fall very far in the winter. This car will be going to Ontario next year so we'll top up with G12 then. Thanks for your contribution to the thread here.

[@mattcieplensky5850]

Just saved my life about to order the part and get to working on this! Thanks a bunch!

[@spelunkerd]

Good luck, Matt.

[@mastermoi]

Hey thanks man! Didnt quite follow what you did but this gave me the guts to try it by myself

[@spelunkerd]

Yes I totally agree, the comments are a place where I often learn more than in the primary video. Thanks for your note. Regarding the dust everywhere, I usually take a rag with a little brake cleaner and wipe it down. If I am opening critical passages like rocker covers or intake manifold, I usually take a vacuum with a small head, removing dust before so it doesn't fall into areas where the engine can be damaged. I try not to spray sensors or wires with any liquid.

[@spelunkerd]

We're evidently on the same wavelength, since last night I spent an hour reading a great article describing the various models of Jetta, written up on Wikipedia. I should have known it would be there. Thanks for your comment, it's nice to have a European perspective.

[@kurtiswakeland5440]

Mronemanband, he was trying to make it as simple as possible for the non car people. the Leak detector is mainly to check for other leaks.. not just the obvious ones.. all those other things are another job another video another time. too many things at once will really throw off someone trying to do one simple job... Great video!! remove everything in the way so you do not create other complications and you also get to inspect the fasteners/clips and hoses while your at it.. doing this job in the next day or two on my 04 Vw just watching it once is going to make this very simple! Thanks again!

[@spelunkerd]

+Kurtis Wakeland Yes! There's a kind of 'Zen' to mechanical work, where a calm, unhurried, orderly approach helps to prevent lost parts and secondary complications. I can often trace complications back to the wrong starting attitude.

[@FuShendo]

Excellent video, thank you very much. It was very . . . entertaining. ;) I need to do this repair this afternoon, and you probably just saved me at least 30 minutes of assessing things and figuring it out, with bonus peace of mind knowing that it's as simple as I thought. I think I bought too much coolant, though. Maybe they'll take back the unopened one.

[@spelunkerd]

Thanks to you, back. Yeah, I hope some day this plastic problem is solved....

[@wgotthardt]

Generally identical, there was no black metal pipe that seems to be in the way of flange removal in vid (and vortex forum thread). I only had to remove plastic manifold/engine cover, the one smaller air box pipe, the sensor connection, and the three hoses. Flange basically disintegrated upon removal. Thanks again for excellent video.

[@pepintechnlogy7965]

Thanks for the video and the answer! I am fixing this today, I have the replacement part, G12++, distilled water, etc.

[@spelunkerd]

Thanks for your reply, John. I've been waiting for you to post another one of your excellent automotive videos, but you are mostly doing other things. Yeah, it's disconcerting that this problem is recurrent. VW should take the ball and design and retrofit something better! Perhaps a true gasket, though the double gasket problem would be an issue unless they redesigned the flange as well....

[@hcoalex18]

It turned out great! I ran into a problem because I have a 1,8L turbo engine and there was a small bar in the way of the flange but now it runs great and no more leaks =)

[@Thecheckmate777]

Great Tutorial because ur straight to the point and thorough! keep em Coming!

[@spelunkerd]

Thanks, man.

[@pastordiaz]

Just finished to replace mine. Thanks for the great video.

[@spelunkerd]

I'm glad it helped, thanks for the feedback.

[@binnsh]

Same part went bad on my 91 MKII Jetta, nice to see that some things don't change. Maybe VW will get around to it someday!

[@spelunkerd]

Those are very kind remarks. Thanks you so much!

[@spelunkerd]

Thank you, Alex. I hope it works out for you -- let us know how the repair turned out.

[@crusermilt]

Great video... Wish you could have explain how to replace an exhaust intake on a 2000 VW Jetta TDI. Again one of the best car repair videos i seen yet!

[@spelunkerd]

+Milton Pope Thanks, man.

[@josealc87]

Milton Pope I

[@spelunkerd]

That's good information, thanks for posting it here.

[@spelunkerd]

What a kind remark, thank you.

[@spelunkerd]

You're welcome, and thanks for watching.

[@spelunkerd]

I'm glad it helped, thank you.

[@spelunkerd]

You make a very good point. Indeed, all the info I have about that comes from a corporation who have a lot to gain from selling coolant for the lifetime of their vehicle. It would be nice to have unbiased, objective data....

[@claydoten7804]

Solid video. Made this repair a snap. Thanks so much!

[@spelunkerd]

Clay Doten No problem, thanks for the feedback.

[@spelunkerd]

Thanks for the compliment. Unfortunately I have no experience with the transmission on this vehicle. Yes, a reasonable first step would be to check the trans oil level, and inspect the oil for debris or color change. You might get a more detailed and qualified response if you were to search out a VW forum. Your problem sounds serious, I hope it can be fixed.

[@REKT_Industries]

Thanks,very helpful , i have the exact same problem, same crap plastic as the intake flange.

[@spelunkerd]

Yes, it's possible, but of course not the only possibility. When coolant level drops low, sometimes the coolant temp sensor can give spurious data. I would start by refilling with distilled water and burping the system, then restart the engine and look for a leak. If you have access to a pressure tester that could be done, too. If you do isolate a coolant leak then I would fix that, and hope that all is repaired with that. Good luck.

[@spelunkerd]

Yes. I did a couple more videos going into how this works. Watch "Hidden genius behind the engine cooling system", and "Mystery of the gurgling heater core". Also Ericthecarguy did videos showing how this works. The commonest cause of overheating after working on a cooling system is trapped air, and it could cause major engine damage if not burped. There is an automatic burping property to modern systems, but huge volumes can't be cleared instantly. It takes a few heat/cool cycles.

[@darryljackson8648]

Totally awesome video. You saved me $100's of dollars on repairs and possibly my job. I can't thank you enough!

[@spelunkerd]

Darryl Jackson Thanks, man!

[@lokote13ish]

thank you sir, this video helped me so much I just finished replacing my cooling hose.

[@spelunkerd]

I'm glad it helped, thanks for the feedback.

[@gxjsgxjs1772]

Great video. Helped me greatly. Just one variation on my 2000 Jetta AEG - the top nut holding the coolant flange had two nuts on it. You have to take the first nut off (without the bolt attached) which will allow you to move the black tube. Once this first nut is removed, you can move that black tube ( which has a little metal bracket attached) out of the way so you can get your socket into the second top nut/bolt that holds the flange in place. Everything else is exactly the same.

[@spelunkerd]

Thanks for dropping by to record your experience. Notes from guys like you help everybody.

[@spelunkerd]

Remember that the coolant reservoir level will fluctuate, sometimes rising higher when the vehicle is really hot. So, if you are already at the very top, you will overflow coolant onto the ground in that case. Better to carefully keep it above the low level but not too high. That way when the level rises, after the vehicle cools the excess fluid will be drawn back into the cooling system when the cooling fluid inside contracts. Thanks for the good question!

[@ivancall5363]

Thanks for posting -- nice to see what I'm in for

[@artbenavides66]

Very informative, this guy is a pro!

[@spelunkerd]

Thanks!

[@wgotthardt]

Great stuff, very helpful....thank you. Repair completed 11/11/12.

[@MrJandin87]

thanks for making videos like this one. . helps a lot. .

[@spelunkerd]

I researched that issue regarding this specific topic. In general using RTV on rubber gaskets is usually frowned upon, and my local dealer does not put it there. I tried to mimic what the dealer does. I'm a little surprised at how low the torque spec is for that flange, presumably because the plastic may be distorted with excessive torque.

[@LifeInElSalvador]

Great Job! Very well explained too. Thanks !

[@karenstine8851]

I am impressed You've clearly showed and explained Now can you just come repair mine

[@spelunkerd]

In retrospect I guess I could have just slapped the part in, but it was nice to be sure. Thanks for your comment.

[@spelunkerd]

Do I understand the question? The large hose the connects the rad to the flange is connected on both ends by hose clamps (on my car). You squeeze the two ears of the hose clamp, then slide the hose clamp to the soft part of the hose, then release. Then you twist the hose and try to loosen corrosion. At 07:01 I show how to use a pick to loosen corrosion between the hose and the flange -- that works for most hoses. At the connection to the rad, i would take off the plastic cover to see better.

[@mcklanepennell7977]

Great job on your own

[@Richardmhwsa]

Thank you so much! Great video. Made the repair much easier.

[@spelunkerd]

You're welcome!

[@spelunkerd]

Thanks for the 2004 update. Was everything else pretty much the same?

[@stefanrosu7482]

tx very much you are the only calm and very detailed adviser that i so on youtube!!!! now let me ask you how do i change the transmission oil please. a have this weird problem with my jetta 1.8t 2002 she doesn't go revers and she has some difficulties when change the shifts from 1-2-3 before when the engine wash hot the reverse was working now is not doing that even if is hot .... pls if u have the time to tell me if can be the oil. tx and do what u doin coz u are the best in that!!

[@AleLovesNYC]

you are awesome! really good video!! a lot of details! I may need to do it. I have a vw golf MKIV and I noticed some cooalant almost in the same place where you had, not so much, really a few of it, the level of cooalant is also stable and the engine doesn't overheat. However I may try to do it and check just in case.

[@spelunkerd]

I'm glad it helped, thanks for the feedback. I think the commonest problem is a stiffening of that rubber integrated gasket. Marked heat/cool cycles cause degeneration and loss of elasticity of the gasket over years of service. The torque spec is pretty low, much lower than typically seen for older style metal flanges.

[@karentid232]

My friend will fix mine 2006 2.0L Turbo Jetta, if I tell him where the 2 sensors are. It's this the 2006? Please say it is.

[@spelunkerd]

@@karentid232 This one is 2001. I don't know if the 06 was the same but I do know this was a known defect affecting multiple years. Check for crusty coolant residue in that area to look for evidence.

[@karentid232]

@@spelunkerd Thank you for your quick response. Hopefully he'll find them so I can stay away from VW's bill.

[@Roby51423]

this was a great help on me i just did the same for a customers car but i went to the auto part for the sensor o-ring and they didnt have it so my question is can i just use any o-ring that fits? if so then thats what i will do. thank u

[@spelunkerd]

I don't remember whether it was on the inside or the outside, but I would try to reproduce what you had before you fix it. I saw a set of still shots where a guy used RTV, and it seemed to work for him. But the dealers don't normally use that -- I asked my dealer and he said they don't do that. I also wondered if a tighter torque would be better, but I didn't find anything to support that either. Presumably there is a risk of breaking the plastic or distorting the seal. Thanks for your remark.

[@spelunkerd]

Sorry for not getting back to you right away since I've been traveling. If you can't find a replacment O-ring I would reuse the old one. The good thing about that part is that it is easy to replace after, without tearing everything apart. And, it should be easy to detect a failing O-ring at the coolant temp sensor just by looking closely for leakage (or, crystalized debris that results from evaporated coolant). Cheers.

[@donshade]

Great video... I changed my flange but I must have disturbed another hose because my power steering stopped working. Is it possible I cracked one of the brittle vacuum hoses?

[@chuckhelms5248]

great video. my 91 Jetta eco-diesel has developed a leak in the same place at the flange. Any words of wisdom before I take it apart. Your step by step process was very helpful

[@spelunkerd]

Diesel engines run hotter and so I'm not surprised to hear that. Before jumping in I would get a copy of the dealers manual - electronic copies from third parties are much more reasonably priced. I use Alldatadiy but I believe Mitchell is also competitive. Good luck!

[@chuckhelms5248]

spelunkerd thanks will do

[@johnstroman36]

Very well done video. I like your methodology as well as the video quality. Very well done indeed. If I had any concern it is that you don't use latex gloves when working. I also agree that it is likely a design flaw -- the use of plastic material probably contributed to loss of fastener tension and subsequent loss of O-ring seal integrity. Anyway, I am about to work on a leak in my car and I found this video to be outstanding. Keep up the good work. Someday, Bently, Haynes and Chilton will figure out that they need to change their business model to pay people like you to make videos like this. Thanks!

[@spelunkerd]

What a kind remark, thank you!

[@josefranciscoesquertalaman3827]

Le saludo desde Sonora, México. Muy buen video.

[@stevehoeing3629]

Thanks for posting and saving me some money!