Blend Door Foam - '96 Passat B4V No Heat

After searching and reading a number of posts, I've determined that my issue (new to me, B4V from Florida, now in Michigan) is the deterioting foam (blowing through vents and NO HEAT, only warm). Blend door problem.

I replaced the thermostat a month ago, fixing all coolant leaks and the engine heat jumps right to 190, as it should. But a long trip to Chicago last night (200 miles) yielded only lukewarm air. And winter hasn't even started yet.

Questions:

1. Can I go up through the floor vents? Someone aluded to that
2. Any other suggestions other than ripping into the dash, heater core, etc?

Thanks

Diesel Don

Little heat comes standard with the diesel engine... it's not an option. The downside of efficient use of fuel is few Btu's left over for heat. The 190 you see on the temperature guage is only to mock you. You will never feel anything near that temperature coming out of the vents. It's a shock for initiates who are accustomed to driving their gassers in the dead of winter with so much hot air blasting out of their vents that they drive with their windows open. Crank up the heated seats, punch the recirc air button on the dash and wear long johns. It's one of the reasons my wife hates my car. Swanky shoes and stockings are a no go in a diesel. Better luck with birkenstocks and knee socks. I have a blanket in the back seat that I put over my legs in the dead of winter.

Some folks block the radiator or invest in block heaters and various electrical heaters. I've just decided to live with it.

RT1 said:

Little heat comes standard with the diesel engine... it's not an option. The downside of efficient use of fuel is few Btu's left over for heat. The 190 you see on the temperature guage is only to mock you. You will never feel anything near that temperature coming out of the vents. It's a shock for initiates who are accustomed to driving their gassers in the dead of winter with so much hot air blasting out of their vents that they drive with their windows open. Crank up the heated seats, punch the recirc air button on the dash and wear long johns. It's one of the reasons my wife hates my car. Swanky shoes and stockings are a no go in a diesel. Better luck with birkenstocks and knee socks. I have a blanket in the back seat that I put over my legs in the dead of winter.

Some folks block the radiator or invest in block heaters and various electrical heaters. I've just decided to live with it.

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I am thinking there is something wrong with your car. I would suggest at least to try changing the thermostat. I don't have much real winter experience with mine yet but so far the heat has been acceptable and I do not believe I will be wearing longjohns any time soon.

Its not an issue with it being a diesel. I currently have four TDI's and I've been through a dozen MB diesels. This is a unique problem, which others on the forum have posted about.

Just wondered if there is a way to get at the foam surrounding the blend door without ripping out the dash???

Thanks

Diesel Don

nighthawk62 said:

I am thinking there is something wrong with your car. I would suggest at least to try changing the thermostat. I don't have much real winter experience with mine yet but so far the heat has been acceptable and I do not believe I will be wearing longjohns any time soon.

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What?? No winter experience in Manitoba?? Global warming's gone further than I thought!!

To be specific the heat is adequate, but hardly generous. The measured discharge temp at the vents is 105 degrees at best with air recirc and high fan after a half hour of steady driving in colder weather. That's only a few degrees over body temperature. The colder the interior the longer it takes to get to that 105 degrees. The engine temp indicator remains steady at 190. If you click into defrost that automatically kicks you into vent mode so you're taking outside air at whatever temperature that is and heating it up as best the coil can do. At forty degrees OA that might give me 85 degree discharge. Eighty five degree moving air does not feel warm and once it washes over that cold windshield it is cold. At ten degrees stop and go traffic you'd be barely using any fuel: no fuel, no heat. At ten degrees going 60 MPH with single glazed windows, heat is being sucked out through the glass and body a lot faster than 105 degree discharge air can put it in. Compared to my Mazda gasser (which gushes out 130 degree air at low fan no matter how cold it is outside or what speed I'm driving) the V-dub is an ice box.

I want to see numbers people. What's the delta T for the heater coil? What's the expected rate of rise? They don't put electric resistance heaters in the european models for nothin'. The heat is barely adequate standing still. I'm hard pressed to think that air blowing in is causing the problem but I'm open to the possibility there's a design flaw in the fan/ducting.

RT

Notice these words from oilhammer on another thread.....

'When all the foam blows off the temp blend door, it can no longer duct the air through the heater core, and you get no (or very little) heat.

The doors are full of holes, and are covered in foam (very common design in many cars). It keeps them lighter and the foam allows for a cushioned operation. Once the foam goes away, the air blow right through the holes.

If you saw the HVAC case out and apart, it is very clear how it works.

Now, what I always found odd is that Valeo is the supplier for HVAC cases for both Chrysler and VAG. Yet VAG products hardly ever have evaporator core failures yet Chrysler does almost constantly. And I have yet to see a Chrysler HVAC door's foam blow off, yet it happens somewhat commonly on VAG products. Go figure.'

That is exactly my problem. My three other TDI's are fine, plenty warm/hot.

My question again is whether or not one can rig something up by going through the floor vents

Thanks

Diesel Don

Feel both of the heater core hoses, are they the same temperature ? You have to remove the lower, center section of the a/c, heater core assembly. That requires removal of some of the center control. Go to wal mart or some craft store and get something called Presto Felt which is a velt material with a peel off sticky back. Cut it to size, squeeze your hand into the opening of the blend door area and try to get the material about centered on the door. You just really need to cover the holes in the door.

Thanks!

Diesel Don

I'm intrigued now. Maybe I'm maligning the heaters capability unfairly...

ninedee_golf_tdi said:

Feel both of the heater core hoses, are they the same temperature ? You have to remove the lower, center section of the a/c, heater core assembly. That requires removal of some of the center control. Go to wal mart or some craft store and get something called Presto Felt which is a velt material with a peel off sticky back. Cut it to size, squeeze your hand into the opening of the blend door area and try to get the material about centered on the door. You just really need to cover the holes in the door.

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Those doors remind me of an old girlfriend...she could be felt but she couldn't be suede....

I don't know about the heating capabilities being so luke warm. My B4V will absolutely cook me out in nothing flat!

MarsBar said:

I don't know about the heating capabilities being so luke warm. My B4V will absolutely cook me out in nothing flat!

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The same with mine. I am nearing the 500k mark and I drive about 80 miles one way to work and last year when it was about 10-15 below zero I had to turn the heat down after about 20 miles. Joe

you can inrease the concentration of antifreeze to get better heat faster but remember to reduce it in the summer.

Would this also be a problem on the A3 Jetta?

sootwagen said:

Would this also be a problem on the A3 Jetta?

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Did you ever see black foamy stuff blowing out of your vents? If so, you should expect to have the described blend door problem sooner rather than later. I think spraying a microbicide into my vents hastened the detachment of the foam?

diesel300dmanual said:

..........
2. Any other suggestions other than ripping into the dash, heater core, etc?

Thanks

Diesel Don

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I'm assuming you've confirmed proper operation of the recirc door (a common problem with these cars)? If the door's closing as it should, do you really think a thin line of foam gasket is really going to make a big difference in the temperature of the air coming out? IMO not worth the work involved to replace it.

Where is that recirc... door?

thanks

Don

VWWV said:

Did you ever see black foamy stuff blowing out of your vents? If so, you should expect to have the described blend door problem sooner rather than later. I think spraying a microbicide into my vents hastened the detachment of the foam?

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No, and my A3 isn't a diesel. I was just curious as to whether the A3 ventilation system is vulnerable to the same age-related issue as the B4.

sootwagen said:

No, and my A3 isn't a diesel. I was just curious as to whether the A3 ventilation system is vulnerable to the same age-related issue as the B4.

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Yes. I also believe some A4s have had the same problem.

diesel300dmanual said:

Where is that recirc... door?...

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Under your cabin air filter, under the hood, against the firewall, right side.

You can hear if it's working or not without opening the hood. Simply put the fan on high and push the recirculation button. There's a significant change in airflow niose when the door closes or opens. No change, no workie