Thankfully, it's not difficult at all to keep your sunroof's drains and seals clear
This happens more than a few times, where someone with a sunroof takes a short trip through an automated car wash. Everything goes smoothly until the sunshade goes back, only to greet the driver (and passengers) with a deluge of water instead of sunlight coming through the sunroof. Convertible owners probably won’t get caught in this situation, for the overwhelming majority would never think of taking this water-logged cruise. But owners of cars equipped with a sunroof or glass roof can run into this on a regular basis, usually thinking, “It’s a sealed hardtop. What could go wrong?”
First, read your owner’s manual. Some will include a warning about taking a vehicle through an automated carwash, but unfortunately for the wet-seated, not all. While a glass roof panel may seem watertight from a glance, looks don’t always hold water.
Factory-installed units contain a trough that runs around the entire perimeter of the inside of the frame. Located at each corner of this trough are water drains, with small-diameter rubber tubes attached. These tubes allow any water collected in the trough to harmlessly exit the vehicle at the undercarriage.
However, the inner diameter of these drain tubes are small enough that they can easily be overwhelmed with a sufficient volume of water, such as the deluge from most car washes. As high water pressure may push moisture past the sunroof seals, often water can collect in the drain trough and overflow onto you and your passengers.
To completely eliminate these risks, you can simply avoid automated car washes. But if you like taking chances, there are a few things to do to improve your odds. First, clean the seals at least once every fairweather season. Dust, dirt, and grit can easily become embedded in the rubber seals that are exposed when the roof is open.
These particles can easily reshape the seals to allow gaps, but damp microfibre cloth and very little elbow grease is all it takes to clean them up. If you notice any debris lying in the bottom of the trough, a vacuum cleaner with an upholstery attachment can make short work of the problem. Finally, a quick shot of silicone lubricating spray can help bring dried out seals back to life.
Running about a cup of water in each of the 4 corners of the sunroof trough, with it open, can help verify if the drain tubes are clear or blocked. Look for the water to drain out from the undercarriage just behind the front wheels and just ahead of the rears; if one appears blocked, a gentle blast from an aerosol can of electronics air-cleaner may do the trick.
If not, resist the temptation to increase the length of the compressed air shot as it may damage or dislodge the tube.
