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Thread: Windows wont defog in extreme conditions

  1. #1
    Join Date
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    1978 635Csi, 1988 735iM

    Windows wont defog in extreme conditions

    So first off you guys just stay helpful to all us here on the board trying to keep clunkers going haha.

    My car was brought back from the dead as some of you know and one of the first things I had to do was replace the heater core. I also repaired the two stepper motor mounts on the top of the ihka housing and ensured they all moved freely.

    Now that were getting rain almost every day Im sadly noticing the car seems extremely lacking in the defog arena.

    On a cold day the windows will fog up but if the suns out you can pop a window and take care of it pretty easily.

    If its raining though fuhgettaboutit! I can pop the window and turn the defrost on and the windsheild will about 90% defog but the side windows will just stay wet if not get wetter, and the back window never even thinks about it.

    My findings are this:

    Positive:
    The sunroof doesnt leak
    The drains work flawlessly
    The ac drains are VERY clean
    The heater vents have zero coolant in them
    the carpet is bone dry with no signs of ever being wet.
    and the door seals seem relatively quiet (also dont show signs of leaking)

    Negative:
    Theres water int he trunk, not alot, but some. (suspecting taillight gaskets)
    Im not 100% but the ihka could still be working improperly


    My question is this then. Could the trunk having moisture cause the entire cabin to fog up? past that Im out of ideas short of buying all new seals for everything.





  2. #2
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    2001 740iL /1991 E32
    Your compressor coming on?


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  3. #3
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    11/88 E32 750iL+98 E36M3
    does the car have a cabin filter? Did you change that?
    Airflow of fresh air is in front the IHKA flaps below the windshield, thru the cabin, out thru the airholes below the parcel shelf into the trunk, of out the trunk into the open air thru the flaps left and right side trunk bottom next to the fenders
    Shogun tricks and tips for the E32 series are HERE!

  4. #4
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    Yep the compressor runs and defies the windshield to a point but just can’t over come the moisture. And she’s too early, no cabin filter





  5. #5
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    There are drain holes under the windshield which go into the fenders, when these are clogged, rain water can enter the interior in the area where the IHKA goes thru the firewall below the wipers.
    http://i44.servimg.com/u/f44/14/94/56/00/ablauf10.jpg
    Shogun tricks and tips for the E32 series are HERE!

  6. #6
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    Alrighty! I’ll check and report back. Wouldn’t that dampen the carpet or would it go into the ihka box and out the drains?





  7. #7
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    normally it will drop into the carpet, not into the drain pan under the IHKA which has the drain holes, so carpet would be wet then.
    How about coolant level? Is that dropping? If so, then it could be coolant, usually the o-rings on the pipes from heater core to heater valves
    Shogun tricks and tips for the E32 series are HERE!

  8. #8
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    Welp, the windshield drains were totally clear. And the carpet isn’t wet and doesn’t look to have ever been wet.

    i did decide to redo the vapor barriers on the doors after I popped the sunroof today and felt quite a bit of cold air rushing in around the door handles.





  9. #9
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    Are the door seals o.k.? You can fix that like I did https://www.bimmerforums.com/forum/s...pping-Seal-Fix
    Shogun tricks and tips for the E32 series are HERE!

  10. #10
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    Yep! Used that very how to this summer, quite helpful





  11. #11
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    So I removed the door panels and none of them had any vapor barrier. I could tell someone had been in them because the window track frame in the rear had a loose cross threaded bolt. So I took some time and made some insulated vapor barriers for all the doors and while its hard to tell if it made a difference, we had a cold morning here yesterday and the windows in fact still fogged a bit once the car was warmed up and the defrost button was disengaged.

    Now! My suspicion the whole time has been the trunk and today while prepping for a big trip in the car I decided to pull the trunk mats out andc let everything dry (nothing is WET but it all is sort of slightly damp). Then, once all the mats were out I reached to grab the little black mat towards the front of the trunk against the rear bulkhead and realized that it was just the top of a giant piece of foam that fills in a cubby in the floor and of course the foam is SOAKED.

    Now, three new questions. Is there a way for that much moisture to make it from the trunk to the cabin and cause the fog headache?

    What is the likely cause there besides the trunk seal which admittedly isnt great?

    AND, why is that cubby there and rendered useless by packing it with foam? Are there higher models that have a little cubby door and storage tray down in there?





  12. #12
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    The key to demisting (even when your trunk is damp) is a fully working A/C system - not only should the compressor run but it should have the right amount of refrigerant and be able to pull the evaporator down to low temperatures to remove moisture from the incoming air.

    The first indication of low refrigerant (in the UK) is steamy windows - and a fully working system will clear the windows of moisture even if the carpets are damp. I would recommend getting the system re-gassed with one of those automatic machines and get a full charge and a health check on the system.

    I think your damp trunk is a separate problem!
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  13. #13
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    So I think you may be onto something there Timm. Though everything works I’m not absolutely certain it’s working right.

    Howrver, I’m sitting in Columbus Ohio tonight after a seven hour road trip through almost constant rain and I had literally zero fog the whole way! It’s rainibf now so I’ll see if the trunk has any water inside in the morning. Before the trip I’d removed every piece of trim and dried it out thoroughly so hopefully if there’s water I can find where it’s getting in too.





  14. #14
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    I would be checking rear sunroof drains and rear window for leaks.
    Time to get in the boot with a torch and get a (trusted) friend to hose down the car

  15. #15
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    So we just took the car on a 7hr road trip to my girlfriends parents place in Columbus Ohio and had a very unexpected journey to say the least. I’ll be doing a whole write upon it. But needless to say the windows were great! Redoing the vapor barriers no doubt did it, possibly drying the trunk helped.,which also allowed me to realize when the car sits still water runs under the trunk seal from the corners where it hits the rear window as the seal is lifting there.





  16. #16
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    you can fix the trunk the the same way as the door seals. They shrink over the years. Here is a write-up for the door seals, same procedure for trunk seal, just cut it and move it back into position. https://www.bimmerforums.com/forum/s...pping-Seal-Fix
    Shogun tricks and tips for the E32 series are HERE!

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