Checking & Preventing Sunroof Leaks: Why drains that slurp are better

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I’ve been reporting on used cars on a weekly basis for many years, and in that time, I’ve come across several curious issues that seem to pop up time and again regardless of the make or model of vehicle. These often include things like transmission hiccups, software and sensor-related issues, oil consumption, and battery trouble. Regardless of what people drive, these are some of the more serious issues that pop up fairly consistently in my research of used cars and trucks. Of course, the very vast majority of used cars and trucks won’t have problems like these — but as a shopper, it pays to be on the lookout nonetheless. 

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One rare but consistent problem you’ll find is the dreaded sunroof leak. Reported by owners of everything from Volkswagens to Kias to Chevys, sunroof leaks can be a source of frustration — not to mention rust, mould, electrical system damage, and of course, sopping wet carpeting. Sunroof leaks are almost always a bad time because they can be difficult to diagnose, particularly irritating since there’s water involved, and also, very expensive to fix. They can also cause extensive damage to your vehicle, reducing its safety and resale value.

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The sunroof in your car or truck consists of a piece of glass on a motorized track, mounted to an assembly that’s embedded within an opening in the roof of the vehicle. That upward-facing opening can collect water when it rains or snows, or when you go though a car wash. Imagine being parked in a rainstorm for hours — even if your sunroof is closed, some of the standing water on the roof of your car will make its way past the exterior glass seal. This is normal. 

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To keep it from overflowing, drainage channels are installed to the sunroof opening. As water builds up in the sunroof opening, gravity feeds it into one of several drainage holes built in. These holes connect to plastic or rubber tubes that route the water harmlessly through the car’s body and down to drip out on the ground below, usually near each wheel.

Over time, this drainage system can become blocked or plugged with debris like sand, sticks, bugs or seeds. With such blockages, accumulated water can’t drain out of the sunroof as quickly, if at all. In heavy rain, or during a car-wash, the sunroof opening could overflow, allowing water to leak around seals and elsewhere into the cabin.

Depending on numerous factors, you may notice water leaking through an overhead dome light, elsewhere in the ceiling liner, or appearing in the footwell carpeting of the vehicle. A small trickle of water can find its way into your vehicle, and go unnoticed for weeks.

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Water leaks to the interior of the vehicle can cause staining, mould, a permanently-humid cabin, foul odours, rust, electrical problems, reduced resale value, and even fires.

Fortunately, protecting yourself from the usual causes of a sunroof leak is relatively simple — if you know what you’re doing. If you currently own a car with a sunroof and it’s not leaking, spending a few minutes a year can help keep it that way for the long term.

Open the sunroof and pour some water carefully into the trough around the opening. This will help reveal the location of the drain holes, if they’re not immediately visible. Usually, sunroofs have four drain holes, one at each corner. If the system is working, you’ll see water flowing down the drain holes and notice it leaking out near your car’s wheels.

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Once you’ve found the drain holes, clean them. You’ll need something stiff, long, and flexible — but not sharp, lest you pierce the tube and let water seep where it shouldn’t. I like to use a piece of electrical wire, or weed-whacker wire.

Next, clean the holes. Carefully fish your wire in and out of each hole, being gentle. Move the wire up and down to clear away any debris that might be built up. If debris is visible in the sunroof opening, remove it with a shop-vac, or by flushing it down the tubes.

If you have an air compressor, a blast of air can help clean out the drainage tubes, too. Clean and flush the drain holes until water flows easily out of each one.

In some cases, you’ll hear a humorous slurping sound as the water drains from the sunroof. Remember: sunroofs that slurp are better. The slurping noise is one sign of a healthy sunroof drainage system, though not all will do this.

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The cleaning procedure takes about 10 minutes. Do it on an annual basis, and you dramatically reduce the likelihood of ever having a sunroof-related leak. And remember: listen for the slurp!

If you’re buying a used car with a sunroof, open it and check for excessive debris within the sunroof opening. Inside the vehicle, carefully inspect the ceiling liner, dome light, a-pillar covers, and upper roof edge near the windshield for signs of mouldy smells, water staining, or dampness.

Next, remove all floor mats, and all items from the vehicle’s trunk or cargo area. Inspect all carpeting carefully for moisture. Move to the cargo area, and lift the cargo floor or trunk floor cover. You’ll likely see the vehicle’s spare tire here, and some bare sheet metal beneath it. Check this area carefully for signs of rust, moisture, or standing water. The spare tire well is another common place for water to collect if there’s a leak. Finding evidence of a water leak in a used vehicle you’re considering is a good reason to move to another unit.

Now you know how your sunroof drainage system works, how to keep it healthy, and how to check a used car for problems with the sunroof drainage system.