Heat causing windows to fog

PeteFalk78 · 06-02-2015 9:16am #1

Hi,

My 2001 Passat has started to fog up when I turn on the heating. There is definitely something going on and is not your standard run-of-the-mill condensation.

My coolant has been dropping slowly over the past year (refill every 3-4 months) but the fogging up has only started in the last 2 weeks. I can't say I smell antifreeze when driving.

Could it be my pollen filter or perhaps the dreaded heater core?

corkgsxr · 06-02-2015 10:04am

I'd bet on heater core.

PeteFalk78 · 06-02-2015 12:49pm

Ok I'm a motor noob so excuse the potentially obvious questions

Considering it requires a dash removal (which isn't gonna happen)

1)Other than keeping an eye on the coolant should it be ok to keep driving
2)Heat is optional to me

- I presume if I keep the heating off then the car shouldn't/wont fog up.

Atlantic Dawn · 06-02-2015 12:52pm

When are they fogging up? Is it first thing in the morning when heat turned on? If you were out middle of the day, no rain and then turned on heat would they fog up? Do you have air con in the car and do you use it? When was pollen filter last changed?

PeteFalk78 · 06-02-2015 1:04pm

Atlantic Dawn wrote: »

When are they fogging up?

Is it first thing in the morning when heat turned on? If you were out middle of the day, no rain and then turned on heat would they fog up? [/QUOTE]
Fog up the whole time - any time of day. Any time I put on heating. When the car isn't being used the windows don't fog up. As soon as I turn on heat - instant fogging up.

Atlantic Dawn wrote: »

Do you have air con in the car and do you use it?

Don't have air con

Atlantic Dawn wrote: »

When was pollen filter last changed?

I've never changed the pollen filter and unsure it it has ever been done

PeteFalk78 · 07-02-2015 12:55pm

I've cleaned the pollen filter and it seems to have cleared the problem

Skatedude · 07-02-2015 1:03pm

using air con can help a lot as air con systems have a dryer which removes moisture especially in winter. not a fix but works

demanufactured · 08-02-2015 3:26am

PeteFalk78 wrote: »

I've cleaned the pollen filter and it seems to have cleared the problem

Replace the filter!

Diemos · 10-02-2015 8:22am

As above, replace the filter cost less than €10.

GalwayRonan · 16-02-2015 8:17pm

Do you have a leak in your car...this can cause car windows to get fogged up...

PeteFalk78 · 17-02-2015 9:00am

Hi Ronan,

I bought a new pollen filter and it has cleared the problem. I was worried that it was a leak in the heater core because it didn't gradually get worse. Luckily it wasnt.

harper61 · 09-10-2021 11:37am

My 2004 Passat has a/c, until now condensation was absolutely no problem but recently the windows fog up really badly immediately the heater is turned on. The only way I can drive is to tun heater to coldest setting & use the a/c.

There is no leak, the carpets, incl. boot, are dry & I've changed the pollen filter.

Could there be a leak under the battery tray?

Atlantic Dawn · 09-10-2021 3:49pm

https://www.boards.ie/discussion/comment/117996914#Comment_117996914

I presume you are also running fresh air through the car and not recirculated?

I'd start by checking the carpets in the car and the boot to see if there's any dampness. Are you sure the air conditioning is actually working?

Cass · 13-10-2021 8:19pm

Have you hot air from the heater?
Is there a smell when the heater is on/blowing?
Have you, as said above, checked the carpets front and back for dampness/wet, and by check I mean pull them back a little to check under them? (as you could have dry carpets on top, but water/moisture under)
The twin rubber pipes from the engine to through the firewall should both be hot, when at running temp.
Any loss of coolant, no matter how little?

Any of the above could signal a heater core issue. Failing any of the above issues it could be a number of other things.

As said above check the recirc air settings.
Check door seals and sunroof, if you have one, for block drains.
Check the antenna base for damage/perishing.
AC drain is blocked.
Foam gasket around the pollen filter "housing"

Heat causing windows to fog

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