Rick's Free Auto Repair Advice

Wet passenger carpet

What causes wet passenger carpet?

There are several types of leaks that can cause a wet passenger carpet. The liquid could be coolant from a leaking heater core, water from the AC evaporator, a leaking windshield seal or a leaking sunroof drain.

Heater core leak can cause wet passenger carpet

A leak in a heater core is usually caused by neglecting cooling system maintenance. Coolant does far more than just transfer heat from the engine to the radiator and heater core. The additives in coolant also prevent electrolysis and corrosion. When you put off coolant changes, the additives wear out and the cooling system corrodes from the inside. That causes pinhole leaks in the radiator and heater core.

Since the heater core is located inside the vehicle, a leak can appear as a greasy film on the windshield and/or wet carpet on the passenger side. The leak onto the carpet is due to the fact that the coolant seeps out of the heater box and drains onto the passenger side carpet. The only fix is to replace the heater core, which often requires removing the entire dash from the vehicle. Then, you must replace the carpet padding and shampoo the carpet to remove the coolant.
To determine whether the leak is water or coolant, rub with your fingers. Coolant will be slippery and have a slight color. Water will be clear.

Clogged evaporator drain causes water to overflow onto the passenger carpet

When you run your car’s AC, moisture from the air condenses on the cold evaporator fins. The water drains down to the bottom of the heater box and out to the ground through a drain tube. However, since air flowing across the evaporator coil also contains dust and bacteria, the water on the evaporator coil can start to grow bacteria and mold slime. That slime slides down to the drain tube and plugs it. From that point on, condensate water continues to build inside the heater box until if finds a seam and causes wet carpet on the passenger side.

To unclog the drain, lay an old towel on the carpet on the

Kool it cleaner

Kool-it AC and heater cleaner

passenger side. Then remove the drain tube and allow the water to run out and soak into the towel. Once the water stops running, use compressed air to clear the drain tube. Then treat the evaporator coil with an antibacterial product like Kool-it.

Leaking windshield seal can cause wet carpet on passenger side

If you have a leaking windshield seal, the wetness on the passenger will be more noticeable right after a heavy rainstorm or right after washing your vehicle. Fixing a leaking windshield is a job for pros. Contact an auto glass replacement company for a quote. They have the right tools and adhesives to do the job correctly.

Leaking sunroof drains can cause wet passenger carpet

All sunroofs leak and the car makers purposely install drains to remove the leaking water. You’ll usually find a drain tube in each corner of the sunroof. Those drains can clog from leaves and dirt. If your passenger carpet is wet and you have a sunroof, check the sunroof drains for signs of clogging. If the drains are clogged, water can run down the outside of the drain, through the front A pillar and saturate the carpet on either the driver or passenger side. Use a vacuum to suck the debris up through the drain tube. Do NOT use a coat hanger to clear the drain—the tubes are just thin rubber and a coat hanger will puncture the tubing, making it leak even more.

©, Rick Muscoplat

Posted on by Rick Muscoplat


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