Symptoms
- Sweet smell inside the car, especially with the heater on
- Wet or damp carpet on the passenger side floor
- Foggy or oily film on the inside of the windshield
- Coolant level dropping with no visible leak underneath the car
Likely causes
- CommonWorn or corroded heater coreThis small radiator-like component inside the dash corrodes and develops leaks with age, similar to the main radiator.
- PossibleDamaged heater core hose or fittingThe hoses carrying coolant to and from the heater core, or their connections, can leak instead of the core itself.
- PossibleCracked heater core from a freeze eventIn cold climates, coolant that's too diluted can freeze and crack the core.
- Less commonManufacturing defect or age-related failureSome heater cores fail earlier than expected due to design or material issues.
What to do
- Check for a sweet smell inside the car, especially when the heater or defrost is running.
- Check the passenger side floor and carpet for dampness or a wet spot, since heater cores are usually on that side.
- Check the windshield for an oily film when the defroster is on, which is a classic heater core leak sign.
- Check the coolant level; a heater core leak often shows as coolant loss without any puddle under the car.
- Avoid running the heater or defrost if you suspect a leak, since it pushes more coolant through the leaking core.
- Have a mechanic confirm the heater core is the source, since a leaking hose or fitting nearby can sometimes look similar.
- Get the heater core or associated hose replaced, since this typically requires significant dashboard disassembly on many vehicles.
Tools and parts
- Flashlight
Heater coreSearch: “heater core for [make model year]”
When to call a pro
See a mechanic to confirm and repair a heater core leak, since replacement is often labor-intensive due to dashboard access requirements.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.