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Windows fog up on the inside

Informational, low priority

windshield fogs up from inside · condensation inside car windows

Symptom description

The inside of the windows or windshield fogs up with condensation, especially in cold or humid weather, or with passengers in the car.

Common causes

  • Normal humidity from breathing and wet clothing/shoes with insufficient ventilation
  • A clogged cabin air filter reducing airflow and defrost effectiveness
  • A coolant leak into the cabin from the heater core (if the condensation feels oily or smells sweet)

What to check

Try running the AC with the heater (most cars can do both at once) - AC removes moisture from the air, which clears fogging much faster than heat alone.

Can you keep driving?

Clear the windows before driving for visibility. If the fogging has a sweet smell or oily film, get the heater core checked rather than just clearing the glass repeatedly.

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Descriptions are for guidance only and do not replace a workshop inspection. If you are ever unsure whether it is safe to keep driving, pull over in a safe spot.

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