Anyone who’s watched a detective show knows that when the blacklight comes out, things are about to be discovered. As it turns out, that applies to car repair, too.
TikTok creator and mechanic Pete (@slapmehard77) recently posted a viral video about solving a customer’s waterlogged 2021 Honda HR-V dilemma using UV light. “I learned something new today,” the creator wrote in the text overlay on-screen.
The video has 2.1 million views and almost 38,000 likes.
“Customer states water pooling on passenger rear floor. Found spare tire well filled with water. Turns out the clues were hidden in the headliner. Never thought to use a UV light for this,” the caption of the video read.
Pete demonstrated the process on camera. “I spent several hours looking for this water leak,” he wrote, panning to a spare tire compartment filled with liquid.
In trying to deduce the cause, he removed the interior trim around the spare and hosed down the roof. He even took the car through a high-pressure car wash. No clues revealed.
“As it turns out you can trace the origin of a water leak with a UV light,” he wrote, and he did just that, using a handheld UV flashlight (and proper eye protection gear).
The video showed comparisons of areas of the car without UV light applied (they look fine) and with UV light shining (water stains are visible).
The culprit, according to Pete? The spare tire well had filled with water from a previous sunroof drain issue. When the driver stopped the car, water would slosh out onto the floor of the backseat.
“My buddy’s 98 accord has wet floors but the headliner looks fine. Imma need him to use his black light I gave him for uranium glass,” one commenter wrote.
“That’s pretty awesome tip about the UV light … I’m gonna order one just to have it in case I ever needed it,” another commenter wrote.
Most viewers reported that they’ve seen sunroof drainage issues like this one before.
“This is why I will never own a vehicle with a sunroof. They all leak eventually,” a viewer chimed in. Another viewer responded, “Clean the sun roof drains it takes 3 seconds. My car is a 15 year old bmw and it doesn’t leak.”
“In our car, one of the roof drainage openings that comes out the back had slipped out of its holder and was hanging inside the vehicle,” another person commented.
One person wrote, “my grandpa’s car has a sunroof and makes a sloshing sound too, the sound drives me mad. thanks for the vid, imma go check it out now!”
Another viewer offered, “ive got a 22 year old car with a sunroof that still doesnt leak. did technology regress? im hearing about way too many sunroof issues in new cars.”
“Bought a used CRV and returned it the next day because of water sitting with spare tire when we got home from dealership. They said ‘we must have washed the spare & it wasn’t dry when put away,’” someone commented.
“I just drilled a hole in the trunk to let the water out and moved on with life. it’s worked great since,” a viewer wrote.
“The UV light trick was just something that popped in my head when I was trying to answer the question ‘where did all this water come from?’” Pete told the Daily Dot in an interview over TikTok direct message. “In this case you could clearly see that the sunroof drain had backed up, the water then traveled across the headliner to the C pillar, and from there into the spare tire well. It’s hard to say if this would work in all scenarios but it’s just another useful tool for diagnosing leaks.”
UV leak detection is a common practice—you can find plenty of kits online, including on Amazon. It’s often used in HVAC repair scenarios. Many such UV leak detectors use fluorescent dyes to find pesky leaks, according to JB Tools.
“If an object contains chemicals called phosphors, which absorb energy and re-emit it as visible light, a black light will make it appear to glow,” according to Sciencing. “Black light emits [most] of its light waves just beyond the range humans can perceive, in what is known as the ultraviolet (UV) part of the spectrum. A black light converts UV light into visible white light as a form of radiation. When a UV light wave from a black light hits an object containing phosphors, those phosphors will glow.”
Pete told the Dot that he didn’t use any type of dye in his test. He speculated that any number of things could have made the UV light reveal the water stain—perhaps glue from the headliner, mold, or grease from the sunroof track. Some common substances that glow under UV light are biological fluids, laundry detergents, certain minerals, antifreeze, and anything containing quinine, like tonic water, according to reference website ThoughtCo.
@slapmehard77 2021 Honda HR-V. Customer states water pooling on passenger rear floor. Found spare tire well filled with water. Turns out the clues were hidden in the headliner. Never thought to use a UV light for this. #mechanic #automotivetechnician #waterintrusion ♬ Five Nights at Freddy's – The Newton Brothers
Pete told the Dot, “I make these videos for sheer entertainment. After being in the field for so long I started to feel like a robot. TikTok just became my outlet. I will be a sad sad boy if they decide to enforce a ban on the app.”
The Daily Dot reached out to Honda via email.