If your vehicle is showing gurgling or waterfall sound behind the dashboard, here are the most likely causes and the parts you'll need to fix each one.
Air pockets in the engine's cooling system flow through the heater core behind the dashboard, creating a rushing water or gurgling noise. This is frequently caused by low coolant levels, a minor leak, or failing to properly bleed the system after recent cooling system maintenance.
Condensation from the air conditioning system normally drains outside the vehicle. If the drain tube becomes clogged with dirt or debris, water pools inside the HVAC box behind the dash and sloshes around while driving.
The heater core acts like a small radiator behind the dashboard. If it develops a leak, coolant can pool in the HVAC housing, causing a gurgling sound along with a sweet smell and foggy windows.
A failing cylinder head gasket can allow high-pressure combustion gases to escape into the cooling system. This continuously forces air bubbles through the heater core, resulting in a persistent waterfall sound.