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Windows Keep Fogging Up

Windows that mist up quickly and clear slowly usually mean too much moisture inside: damp carpets, a blocked cabin filter, recirculation left on or a heater core leak.

Normal risk

Fix it soon: poor visibility is dangerous.

Short answer · Why do my car windows fog up so much?

Moisture from breath, wet clothes and damp carpets condenses on cold glass. Recirculation traps that moisture, and a blocked cabin filter reduces airflow. If the mist is greasy and smells sweet, coolant from the heater core may be the cause, which needs checking.

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Safe checks you can do

  1. Use AC and fresh airAC dries the air even in winter; turn recirculation off.
  2. Check for damp carpetsWater leaks keep the cabin humid.
  3. Wipe the glassA greasy film suggests a heater core leak.

Questions that narrow it down

  1. Greasy film on the windscreen?Coolant.
  2. Wet footwell?Water leak.
  3. Is recirculation on?Moisture stays inside.

Possible causes

Listed without ranking. Use the questions above to see which ones fit your car.

  1. Recirculation left onHumid air stays in.
  2. Damp carpetsLeaks or wet shoes.
  3. Blocked cabin filterWeak airflow.
  4. AC not workingAir is not dried.
  5. Heater core leakCoolant mist.

Questions about Windows Keep Fogging Up

Does using AC in winter waste fuel?

It uses a little fuel, but clear windows are worth it.

Should I clean the inside of the glass?

Yes, dirt on the glass makes it mist faster.