Coolant leaking into the cabin floor

Symptoms

• Wet carpet, usually on the passenger side floor
• Sweet smell strongly noticeable inside the car
• Possible dripping visible from under the dash
• Foggy or oily film on the inside of the windshield

Likely causes

• CommonHeater core leaking directly into the duct system or footwellA significant heater core leak can drip enough coolant to actually pool on the floor rather than just create a smell.
• CommonHeater core hose or fitting leaking under the dashConnections under the dash can leak directly into the footwell area.
• PossibleHeater control valve leaking (where equipped)A valve controlling flow to the heater core, if leaking, can drip into the same general area.
• PossibleCondensation drain blocked, causing water (not coolant) to pool insteadIt's worth confirming the fluid is actually coolant and not backed-up AC condensation, which is a separate, unrelated issue.

What to do

1. Confirm the fluid is coolant (sweet smell, often slightly colored) rather than clear water from a blocked AC condensation drain.
2. Check the coolant reservoir level, since a heater core or hose leak of this size usually causes a noticeable drop.
3. Avoid running the heater or defroster until this is diagnosed, to reduce further leakage and interior damage.
4. Have a mechanic inspect the heater core, its hoses, and any control valve as the most likely sources.
5. Get the confirmed component repaired or replaced, since dashboard disassembly is often required for heater core work.
6. Have the carpet and padding dried out or replaced if soaked, to prevent mold or lingering odor.
7. Recheck coolant level and interior dryness after the repair and a few days of normal driving.

Tools and parts

• Flashlight

When to call a pro

See a mechanic to properly diagnose and repair a heater core or related leak, since dashboard access is usually needed and it's not a practical DIY job for most people.

Safety