If you’ve noticed a musty smell coming from your car’s vents especially after it rains or when you run the AC it might not just be dirty filters or a clogged drain. In some vehicles, water can sneak past worn or damaged strut mounts and end up pooling near the HVAC intake, creating a perfect environment for mold to grow. Testing strut mounts for mold infiltration into car ventilation isn’t something most drivers think about, but it’s a real issue in certain makes and models where the strut tower sits close to the fresh-air inlet.

What does “testing strut mounts for mold infiltration” actually mean?

Strut mounts sit at the top of your vehicle’s suspension struts, usually under the hood near the firewall. Over time, the rubber seals in these mounts can crack or shrink. When that happens, rainwater or moisture from washing the car can drip down into the cabin air intake area instead of draining properly. If that dampness lingers near the evaporator case or ductwork, mold spores already present in the air can take hold and start growing. “Testing” here means checking whether your strut mounts are leaking water that could feed mold inside your ventilation system not testing the mounts themselves for mold directly.

When should you check this?

You don’t need to inspect your strut mounts every oil change. But if you’re dealing with a persistent mildew odor from the vents that returns shortly after cleaning the system or replacing the cabin filter, it’s worth looking further. This is especially true if:

  • Your car has had recent suspension work
  • You park outside often in rainy climates
  • The smell gets worse right after driving in wet weather
  • You’ve already ruled out a clogged AC condensate drain

In these cases, water intrusion through compromised strut mounts could be the hidden source feeding the problem.

How to test for water entry near the strut towers

Start by opening the hood and locating the strut towers typically found at the corners of the engine bay, near the base of the windshield. Look for signs of moisture, dirt streaks, or pooled water around the mount area. Shine a flashlight and check the rubber boot covering the mount. Cracks, tears, or gaps between the rubber and metal housing are red flags.

A more hands-on test: on a dry day, pour a small amount of water (about a cup) slowly around the base of each strut tower. Wait 10–15 minutes, then check inside the cabin near the HVAC intake (usually behind the glove box or under the dash on the passenger side). If you see water droplets or damp insulation, the seal isn’t holding and that path could let in enough moisture over time to encourage mold growth in your vents.

For a step-by-step visual guide to this inspection process, including how to differentiate normal wear from problematic leaks, see our detailed walkthrough on how to test strut mounts for mold-related water intrusion.

Common mistakes people make

One big error is assuming the cabin air filter is the only defense against odors. While a clean filter helps, it won’t stop water from entering upstream. Another mistake is replacing the entire HVAC assembly without first checking simpler, cheaper entry points like strut mounts or cowl seals. Also, using compressed air or harsh cleaners inside the vents might mask the smell temporarily but won’t fix the root cause if water keeps getting in.

It’s also easy to confuse symptoms. A moldy smell could stem from a blocked evaporator drain but if that drain is clear and the odor persists, look outward toward body seals. There’s a documented link between aging suspension components and declining cabin air quality in certain vehicles, as outlined in our piece on the connection between strut mount condition and interior air problems.

What to do if you find a leak

If your strut mounts are leaking, you’ll likely need to replace them. Most modern mounts come as an assembly with new bearings and seals. While it’s a job that often requires spring compressors and mechanical skill, some DIYers with experience can handle it. If you’re not comfortable doing it yourself, a trusted mechanic can inspect and replace them just make sure they check the surrounding cowl area for additional damage or debris that might worsen water entry.

After fixing the leak, thoroughly dry out the HVAC plenum. Run the fan on high with heat (no AC) for 20–30 minutes to evaporate residual moisture. Consider using an EPA-registered HVAC cleaner designed for automotive systems never household bleach or vinegar, which can damage sensors and leave residues.

Prevention matters too. Regularly clearing leaves and debris from the cowl grille (the vent-like panel at the base of the windshield) reduces water buildup that can overwhelm even intact seals. Learn more about proactive checks in our guide to assessing strut mount health before odors start.

Quick checklist if you suspect mold from strut mount leaks

  • Confirm the cabin air filter is clean and properly seated
  • Verify the AC condensate drain is unclogged (look for dripping under the car when AC runs)
  • Inspect strut mount boots for cracks, gaps, or soft, spongy rubber
  • Perform a controlled water test around the strut towers
  • Check for dampness or staining near the HVAC fresh-air inlet under the dash
  • If leaking, plan for mount replacement and full HVAC drying

If multiple signs point to water intrusion near the strut towers and you’ve ruled out other common causes it’s reasonable to treat the mounts as a likely contributor to your ventilation mold issue. Fixing the leak stops the moisture supply, which is the most effective way to keep mold from coming back.

Explore Design