Piston Slap: Black Lights, Camera, Action

Sajeev Mehta
by Sajeev Mehta

Rick writes:

I was walking home and passed an independent mechanic shop. He appeared to be passing something like a black light (rectangle case with a “purple” cylindrical bulb) over the rim or tire of an older BMW 3 Series. What’s up with that?

FYI: while I enjoy the column and the rest of the writing, I suggested online that there is some follow up to the problems. I’ve learned a lot about what might be wrong but not so much about what was wrong. Thanks for reading.

Sajeev answers:

Good point: I now email each Piston Slap contributor on the day of their question’s unveiling, hoping they’ll contribute to the discussion. That happens often, but not every time. Not sure what else I can do. Your thoughts?

Now to your query: I haven’t heard of using a black light on a tire, but that’s how any automotive subsystem (that has pressurized fluid) is tested for leaks. Throw some UV dye in the fluid, let it circulate, run the black light over the entire system and bada-bing, there’s your leak. The only true bummer is when you “dye” your air conditioning system and can’t find a leak under the hood: the dye is under the dash in the evaporator. And that fix is almost never a fun job.

While a little OTT, perhaps this patent filing might put it into a better context. Or maybe it’ll “shine some light” on the situation. Thank you, I’m here all week. Please tip your waitress!

[Send your technical queries to mehta@ttac.com]

Sajeev Mehta
Sajeev Mehta

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4 of 7 comments
  • Dkulmacz Dkulmacz on Aug 04, 2009

    This is also used to find leaks in evap systems on vehicles (California regs call for no greater than a 0.020" leak), so it can be used with a gas and not only fluid.

  • Bolhuijo Bolhuijo on Aug 04, 2009

    Urine glows under a black light - it's handy to spot (no pun intended) where pet accidents have happened. Perhaps this guy was just trying to clean the bimmer. (smirk)

  • Maxo Maxo on Aug 04, 2009

    You could also pre/ap-pend any resolutions you hear about from contributors on the next day's piston slap column along with a link to the original column (as this wouldn't necessarily always be referring to the previous day's column).

  • Nopanegain Nopanegain on Aug 04, 2009

    Those are some serious old-school fiberglass IASCA floorboards Sajeev. Nice find.