Since I am dealing with this for the first time, first hand… I thought I would put this out there to other VW and likely Audi owners. I own an 03’ VW Golf GTi…20th Anniversary edition. The heat in this vehicle is POOR…barely lukewarm. ALL of my previous vehicles and even VW’s I tested out, had cabin heat that you could use to Toast Marshmallows upon, not so this VW. I used to say out loud…I thought Germany got Cold in the winter…and it does…lol. This was how my heat was from day one…my suspicion? Bad or clogged heater core…The heater core is basically a small radiator…full of hot engine coolant. This is how heat is produced in pretty much every vehicle on the planet. If you have a leaking heater core…the replacement estimate will make your stomach roll. Its not cheap…why? Because on the assembly line…it is almost quite literally the very first thing installed into the cabin of the car along with the dashboard. The Heater Core is buried DEEP…almost always, some exceptions. So nobody wishes their core go bad and need replacement…even a mechanic like me.

SO…I began by suspecting my core was clogged. I had reason for this suspicion due to my vehicle being abused and water being added to the radiator until its content was 100% water. This is something that should NEVER occur. Coolant serves several purposes on vehicles. In addition to providing liquid for Heat Transfer it also provides corrosion resistance for the engine block…it also lubricates the water pump. Since many modern vehicles drive the water pump with the Timing Belt…you do NOT want your pump to be unlubricated and lock up on you. Like this car that I own now had happen. Seized the water pump…snapped the T-Belt and bent ALL 20 valves in the engine. In fact this is the single reason I own this vehicle today. I repaired all this damage simply to own this vehicle.

After I flushed my radiator and heater core…using mild acids or whatever chemical is used for this purpose I could feel better about my core not being the problem. What I did find out was very interesting and something with which I have never first hand come to deal with

On later model VW’s…they decided to not use a heater core flow control valve…many other vehicles have the same design. In older cars when you adjusted for temperature change…the temp knob or slide was directly attached to a valve that opened and closed to allow or not allow hot coolant to flow thru the Heater Core…and thus affecting a temp change in the cabin. Many cars today did away with this valve and Hot coolant is always flowing through the core. Nowadays Temp control is accomplished by the use of The Blend Door.

OK…fine, the Blend Door controls temp instead of a valve…got it, no problem right? Not in the case of this VW. Not sure of all models affected . THE PROBLEM with my VW Golf Blend Doors? They used metal for the construction of the doors, OK, so what? For some reason the metal they used to construct the doors have HUGE HOLES in them ! They subsequently used a foamy weatherstrip kind of tape to cover all of the holes. WHY ?! I have absolutely no clue…NONE. All they needed to do was use a solid piece of metal or plastic for the door…nothing with holes in it They could then use the foam tape on the edges as a sealing agent, but for some reason they covered the door and its holes completely with this foam tape like stuff.

This foam tape substance begins to break down after about 5 years…it then comes flying out of the vents and usually lands in your eyes while driving. I noticed this stuff flying out of my vents in the early days of ownership, thought little about it…until now, when I went looking for Toasty warm cabin heat. I always enjoyed nice n HOT heat in all my other cars…I mean heat is one of those easy to provide type of things in vehicles. Since my heat simply wasnt even close to cutting it in the cold. This is how I began to research and learned all about the blend doors. There are U-Tube videos now on the subject, but there were no videos I could find back when I picked up the vehicle. So now is a different time with more info and repair solutions out there to view easily. All this can be viewed on U-Tube right now in fact.

If you own any VW and the cabin heat…just ISNT…the problem is the holes that exist in the blend doors and more specifically the degradation of the tape that they used to cover the those holes in the metal Blend Doors…the tape falls apart and now the doors have Big Holes exposed in them. I repaired mine without removing the entire dash and have seen others do the same. I used Aluminum foil tape designed to be used on heating ducts…to cover up these holes permanently THIS allows the airflow to be properly funneled thru the heater core and on toward the proper destinations as dictated by the flow control knob. When the blend door holes are fully exposed…air exits all of the vents simultaneously. This forces you to crank the blower just to feel air flow from whichever vent you chose. When the holes are exposed air flow is weak at best from any location. This is a real problem for many reasons. Why didn’t they use solid metal doors…or plastic…at least use something without big HOLES in it…did they use scrap metal for this? I will never know.

Before anyone is told that they need a new heater core, which can be VERY EXPENSIVE REPAIR ESTIMATE… PLEASE … read the enormous problem description Book I have just written…LOL…sorry. The heater core replacement job will NOT be cheap…and if they do not address the blend door holes…it will function exactly the same as before. This should never occur and I bet some shops simply repair the blend doors and leave the core alone, but charge you just the same. I can safely say that NOBODY, not even mechanics, enjoy doing a heater core replacement very much. It is VERY invasive and requires the entire dash board to be removed typically. This is something that can invite all sorts of squeaks n rattles and other problems afterwards. This is NOT needed in most cases of the VW line of vehicles…my vehicle year is 2003.

This issue is a great way shops can bill you for a big job…and yet have a relatively quick, EZ and productive fix…for all you know they did replace the core. HOPEFULLY this Book I have just written can help you repair the problem and help you possibly avoid a fraudulent repair taking place. Best to simply avoid all of this stuff. Now a heater core LEAK is a different story, these require a new core…but NOT THIS. Not discussing leaks at this time they are an entirely different animal.

Sorry this is so long, but I tried to describe the issue in detail. This rambling post could very well save someone A LOT of money. Saved me a lot of work I can tell you that. Now I can now make Smores while driving ! Jk.


Interesting post. Thanks for the heads up Blackbird! I owned a VW Rabbit years ago, and while I generally liked the car’s esthetics and performance, especially the suspension system, I discovered after repairing it many times that the fuel pump circuit just wasn’t designed properly to handle the amount of current needed to run the pump. Likewise, there was a design problem with the components used for the engine’s valve stem seals. It’s sort of hard to understand how stuff like that could happen, the fuel pump circuit is just a DC circuit after all. Its not rocket science. Likewise with what you noticed, those weird tape-up holes in the hvac deflector doors, you’d think that would get flagged as a problem during the design’s testing phase. I guess there’s a lot to the process of manufacturing cars that isn’t easy for the car owners to understand.

Indeedy George…Sometimes we will never know what is behind the motivation of mfg’s to do what they do or use what they use… Typically its the All Mighty Dollar more often than not. But for the life of me I cannot FATHOM why anyone anywhere would choose flat pieces of metal with large holes randomly all over the place…especially when the entire purpose of said door is to deflect or route air in a certain direction and do so efficiently with little leakage. I understand what that foamy rubber tape could have been used for…it makes a nice seal for the door and its frame or edges…it also cushions its openings and closings just like weather stripping keeping operation nice and quiet. But for Petes sake…to use it in the manner found here ?..Simply Preposterous…in every single manner.

That foam began breaking down prior to the vehicles 7yrs of age…not to mention trap all sorts of dust within it. Made for very interesting stuff to have radomly blown into your eyes while driving. The proper fix is to approach it like a Heater Core replacement…but you can cheat it by going in behind the radio and have acceptable Air duct performance when completed. There must be THOUSANDS of affected vehicles out there right now…and the owners probable dont know whats up because it sneaks up on you. It also not really an intuitive problem to even consider from the drivers seat. You only get it when you see the photos of the guys addressing it on U tube. Then it makes all sorts of sense. UGH…what a fiasco and SO AVOIDABLE…from the get go. I HOPE VW avoids this in the future…it would be insane if they dont.

I think those original Wabbits have the old style tubular Glass fuses? Those suffered from making good contact an awful lot to due getting loose and or corrosion…then it would burn the wire covering off due to the higher resistance created. I never knew about the valve stem seals…sounds like a rubber compound technology issue…or the wrong formulation of rubber used as stem seals…that sucks… Who knows…maybe they cheaped out on the 5 dollar valve stem set.

Again…none of us will really ever know when the Bean Counters are winning over the Engineers during the design phase of Automobiles…we sort of get to figure that out later ! Sounds awful to create such problems to save 25 dollars per unit…but if you make 2 million units… I know that I wouldn’t kick that sort of money out of bed I can assure you of THAT !


Good post. I had an 03 Passat. It starting having minor heater difficulties after about 8-10 years, the floor vent didn’t output much heat, but the others were OK. I dumped it in 2014, so next owner may have more problems.

This is the same issue Bill, no question. Funny how the problem creeps up on you over time as that foam tape degrades and flakes off…and usually blows into your eyeballs while you drive…and Boy Howdy IT BURNS when it gets into your eyes!!! I can tell you that. Glad you never had to get into the repair…I hope some shop does not incorrectly diagnose the problem and Foist a new Heater core upon the new owner.


Very interesting, and pretty much what I’ve been suspecting since I’ve been spitting foam back at my car for the last 5-6 years now. Given this, how likely, does everyone think, that this also affects A/C performance? For the record, it’s a 2004 Jetta.

Backstory: I’ve had A/C issues the last year or so, and according to the stealer dealer, the whole system cabin cooling system needs to be replaced. Compressor, expansion valve, accumulator/drier, and all the bits and bolts in between. All this for the sweetheart of a deal at around 1700$.