facebook pixel

Water Leaking from Car When Heater Is On?

Moisture dripping from car exhaust

Managing problems with cars can be difficult, especially for the average person who doesn't have a mechanical understanding of cars.

Is water leaking from your car when the heater is on a bad thing, and what should you do about it?

In small quantities, water leaking from your A/C system isn't something to worry about as long as it's only a little condensation dripping from the underside of your car.

The exhaust also produces a little water, which doesn't typically indicate an issue; coolant leaks, on the other hand, are more serious, especially if the issue stems from your heater core.

In many cases, you don't have anything to worry about with condensation as long as it's water and as long as it's only a small drip.

If you smell coolant, it's worth diving into the issue more to find out what's wrong.

The rest of this article will dive into potential water leak issues and how to fix them.

Table Of Contents [show]

    Moisture dripping from car exhuast
    Moisture dripping from car exhuast

    Why Is Water Leaking from The Car when the Heater Is On?

    Water typically leaks from the car when your A/C or heating system is on due to condensation produced by the air conditioning unit. The exhaust also winds up, filtering out some water from the engine.

    You'll see water dripping from the front underside of your car or the tailpipe―as long as it's not coolant or dripping excessively, you've got nothing to worry about. Always confirm what is dripping before you try to diagnose the issue.

    If the water is dripping while your A/C isn't on, you might be experiencing the following problems:

    • Clogged evaporator drain

    • Faulty seal

    • Leaking evaporator core

    Clogged Evaporator Drain

    A/C drain hose or evaporator drain hose can experience debris buildup, causing it to clog.

    The first symptom of a clogged drain will be musty or unclean air emanating from the vents and ‘choppiness' in the A/C functionality.

    To fix the issue, you'll need to clean out any buildup and potentially replace the cabin filter.

    Faulty Seal

    A faulty seal in the evaporator system can cause excessive water leaks from your car.

    A clogged filter can also cause corrosion, damaging the seals that allow your evaporator core to work properly.

    Often, fixing a faulty seal requires the replacement of the entire unit.

    Leaking Evaporator Core

    A leaking evaporator core can cause your A/C system to malfunction, blowing air inconsistently or not cooling the air properly.

    If there's a leak in the core, replacement is your best bet for a fully functional A/C system.

    Car AC evaporator
    Car AC evaporator

    What to Do If Fluid Is Leaking from the Exhaust when the Heater Is On

    If fluid comes from your exhaust when the heater is on, the first step is to determine what is leaking since different fluids indicate different issues with your heater system.

    Check whether the fluid is one of these three:

    • Water

    • Coolant

    • Oil

    Water Leaking Out of the Exhaust While the Heater Is On

    A car produces water vapor when the car is running.

    This vapor condenses when the car is cool (aka when you turn it off), causing excess water to drip from the tailpipe.

    If the heater is still on and you notice condensation, it may be due to cold weather.

    Mixing hot engine components and chilly air can cause a whitish mist, and some water drips from your tailpipe.

    This is no cause for alarm; however, excessive water leakage could be due to a blown cylinder head gasket, damaged piston rings, or a faulty EGR cooler.

    Coolant Leaking Out of the Exhaust While the Heater Is On

    A coolant leak can indicate a blown head gasket.

    When the gasket blows, the connection between the engine block and cylinder head is no longer air-tight, allowing coolant to escape through the tailpipe.

    Structural flaws in the head or malfunctions in the intake manifold can also cause coolant to leak.

    Foamy oil indicates a blown head gasket
    Foamy oil indicates a blown head gasket

    Oil Leaking Out of the Exhaust While the Heater Is On

    Bad piston rings or blown head gaskets can cause oil to get where it's not supposed to and leak from the tailpipe.

    Common causes are obstructions in the PVC valve and worn seals in the valves.

    Check that you see oil and not soot. Whether your car is leaking oil or coolant, it's best to take it to a mechanic for inspection.

    How Do You Know If Your Heater Core Is Leaking?

    The heater core circulates coolant and provides heat to the car's interior.

    If you notice the following signs, you likely have a leaking heater core:

    1. A sweet smell

    2. Foggy windows

    3. Cold air in the cabin

    4. Excessive coolant consumption

    5. Cold cabin, hot engine

    6. Wet car floor

    Can You Drive a Car with a Leaking Heater Core?

    For a short period, it's ok to drive with a leaky heater core, but we recommend you use that driving time to make your way over to a mechanic.

    The heater core uses coolant from the engine, which will cause your car to devour coolant.

    A lack of coolant can cause overheating, as well as a bunch of other problems you just don't want.

    Signs Your Heater Core Is Leaking

    1. Your Car Smells Sweet

    If you smell sweet air coming through the vents, you are probably smelling leaked coolant from the radiator.

    2. Your Car Windows Become Foggy

    Coolant evaporates into steam and condenses on your windows when it leaks into your heater, causing your car's interior to become foggy.

    3. Your Car Is Blowing Cold Air into the Cabin

    Punctures or structural damage to the heater core can cause warm air to be diverted away from the cabin before it reaches you, leaving you with nothing but cold air even though the heater is on.

    4. Your Car Uses Lots of Coolant

    Of course, if your car is leaking coolant, it's not being used efficiently, resulting in the need for a top-up much more often.

    5. The Cabin Is Cold, but the Engine Is Hot

    Issues in the heater core can cause it to leech excess coolant from the engine, potentially causing it to overheat. If the engine stutters, idles rough or has poor acceleration, take your car to a mechanic to inspect it.

    6. Wet Car Floor

    When a heater core leaks it tends to make the floor of the car wet.