Heater-core coolant leak into the cabin

Tags: #hvac

Symptoms. A dripping sound from the passenger side, moisture found under the driver-side floor mat, and the heater ceasing to produce heat — together these point to coolant leaking from the heater core or its associated hose circuit directly into the cabin, rather than a rainwater/sunroof/condensate source.¹² Context in this case: the car had a prior air-lock (air pocket) in the heating system, after which coolant had been refilled — a possible link between that earlier service and the later leak was suspected but not confirmed.³

Locating the source. Note which footwell is wet: dampness centered on the driver's side rather than the passenger's side points toward the heater hoses/core routing on that side rather than a more general source.⁴ Diagnostic steps: check the antifreeze/coolant level under the hood first (a drop supports an internal leak rather than condensation);³ then inspect the heater hoses and the heater-core connection points for wetness or corrosion.⁵

Fix. Replace the heater core, or repair/replace the specific cracked/degraded tube(s) feeding it, once the exact leak point is confirmed — most reports in this thread pointed to the hoses themselves rather than the core body.⁵⁴

Related pages

• Heater core — part number and alternatives
• Dashboard panel removal — A/C and heater access
• Heater blower motor fan — no separate part
• Windshield air-intake water leak in rain
• Heater fan motor failure — diagnosis and repair

Sources

This page is compiled from 5 community messages. Every fact carries a numbered reference to its original author and message.

Last updated: 2026-07-24