Symptoms
- Sweet, syrupy smell noticeable when the fan, heat, or AC is running
- Windows may fog up faster than expected
- Coolant level dropping without an obvious external puddle
- Sometimes a faint mist visible near the vents
Likely causes
- CommonLeaking heater coreThe most common source of a sweet smell through the vents, since the heater core sits directly in the airflow path inside the dashboard.
- PossibleLeaking heater hose near the HVAC housingClose proximity to the cabin air intake can let a hose leak's smell reach the vents even if the core itself is fine.
What to do
- Check coolant level in the overflow tank and monitor it over the next several days for unexplained dropping.
- Check the front passenger floor carpet for dampness, a common early sign of a heater core leak.
- Feel the heater hoses at the firewall for any wetness or crusty coolant residue nearby.
- Limit heater use once a sweet smell is confirmed, since continuing to lose coolant risks overheating.
- Have the heater core (or leaking hose) repaired and the cooling system properly refilled and bled afterward.
Tools and parts
Heater core or heater hose for your vehicleSearch: “heater core”
Coolant matching your vehicle's specSearch: “coolant antifreeze”
When to call a pro
See a mechanic if a sweet smell from the vents is confirmed alongside dropping coolant, since driving with an unaddressed coolant leak risks overheating.
Safety
Use caution
Coolant is toxic to pets and children; clean up any spills promptly.