I was waxing the family car last night, late evening so a flashlight was helpful, the trusty Convoy M1, i was washing my hands from the oily dirt (pre washing) and realized why not use cold tap water to cool the head of the flashlight.
It worked quickly and effectively.
Any harm in this?
Well, that would depend on the rating of watertightness, or (since those ratings are almost always bogus) on how properly the O-rings do seat and seal.
Now, I haven’t had a Convoy light myself, yet, but on any Fenix and 4Sevens I’ve had the opportunity to get my hands on, they held up nicely under water. The very same applies for the later $urefire 6Ps (wouldn’t try it with the older Laser-Products 6P, but who of us does actually own one of those, really?) and of course all the clones, most notably the SolarForce ones. No problems with any maglites of any year, too, IMHO.
Check the seals. Are there O-rings, everywhere? If you feel confident about the seals, it’s try and error. I’ve only had one letdown, so far - one of the older tank E007 2xAA; which leaked water past the lens.
I’ve done that too. I don’t think it’s a problem because cooling fins are usually thick and resist warpage well, especially considering that the fins might be max 150 degrees F. And using tap water of 60 degrees isn’t much of a difference.
I actually use my crelant 7g5 v2 for swimming at night. I’ve only ever gone like 6 feet under, but I do it for a good half hour at a time.
most people who are 6 feet under don’t come back 30 minutes later :~
The first sign of water entry is usually condensation on the inside of the lens. If that did not occur, you are probably safe.
My analysis of the M1 tells me it is probably good for just about any nonsubmerged situation except for a high pressure spray.
cold tap water was very effective and surprisingly quick (well not surprising once i thought about it)
A while back I rigged up a water cooling system for my DRY, with it I was able to run the DRY for 24 hours straight with no damage to the light. For anyone wondering all I did was get a 12 volt water pump and some copper tubing, I wrapped the tubing around the heatsink fins and pumped water through it (along with through a bunch of tubing not on the light to give it a chance to cool down) while the pump was powered off the same supply as the light.
It can be a problem...
I was once torture testing UF-980L, C8 and Romisen T602.
I ran them down for about 3-4 batteries on table, changing them on the fly to see if I can fry any of them.
They worked fine but were too hot to touch after the test, so I thougt I could dip them to cool them down.
Tail-first I put them to water, 3" deep. Head was on surface.
They ALL socked water up to the driver level. All of them.
All of them had intact O-rings with lube.
Why?
Heat generates over pressure. When you cool them down in water, it lowers the pressure and they suck the water up probably from around the tailcap boot.
This is my theory...
After all, they all worked fine once I poured the water out. All cells were working also.
Yes, if they are immersed when hot, they will suck in water. That’s why I suggested non submerged only.
If a watertight light starts out in the water, it’s probably going to be OK.
Actually, I thought of a scenario that may let in a little water even in a splash situation. If water splashed on the light sits in the seams where the O-rings are. When the light cools, the cooling air inside will suck in whatever is on the outside of the O-rings, including any water sitting there.
The only lights that will assuredly prevent something like this is a true diving light, maybe a IPX7 (2m safe) or IPX8 (min. 2m safe) light.
Very interesting, i never thought of that, i instinctively avoided getting water on the openings where the o-rings are because if water was to somehow get in, that would have to be the entry point, but this scenario seems plausible.
Time to call mythbusters 
I can't speak for these dry orings, but I deal with silicone-lubed rubber o-rings with pools alot, and I don't think I'd recommend letting the water get any of the seals. The rubber is notorious for expanding/contracting with temperature changes. It's gonna do this at a different rate than the metal...so I could be totally wrong, but I can see that possibly letting water slip past the o-ring.
Does anyone know if the ipx8 rating on crelant lights is always true? It seems to work on mine…
Don’t really notice a difference between an ipx8 rated light and a normal light, except for having thick orings.
Try Dow Corning 111 silicone grease. It has a putty-like consistency. I used some on a tight o-ring and it got even harder to screw together.
“It can be used as a sealant in applications such as vacuum and pressure systems, equipment subject to washing and harsh environments, electrical service entrances and underground connections, and transformer gaskets and equipment enclosures.
Dow Corning 111 Valve Lubricant and Sealant maintains a serviceable consistency from approximately –70° to 400°F (–57° to 204°C)…”
(ice) cold water is great for chilling beer….but flashlights???
ice cold is not needed, just room temperature is more then adequate, i put it under a running tap
Submerging just the tail used to do wonders when I ran runtime tests on my smaller lights. I used to pour an inch of water into a cereal bowl, tail stand the light in the bowl, and let it run. The head usually never got above lukewarm.
I’m not sure what the practical use for external water cooling would be outside of stuff like doing extended runtime tests. If you’re using a light outdoors, the combo of the night air and heatsinking through your hand is enough to keep most lights reasonably cool.
interesting idea
i also noticed that outdoor it doesn’t get as hot as indoor, i didn’t think slight air movement could cause so much heat dissipation
A light that would leak this way might be called water resistant but certainly isn’t waterproof to any depth. Watches are often rated to 100m that can’t stand a trip through the shower. O rings should either be under compression or contact mated surfaces rather than threads and always need to be cleaned and relubed prior to immersion.
Myth busters is an entertaining show but I wouldn’t put too much stock in their results. Their science is not good often using tests that don’t scale well or drawing doubtful conclusions from poor modeling. They’re not always wrong but often enough not to rely on. But it was fun seeing them blow up a concrete truck.
Really?
i think they sometimes draw broad conclusions based on their tests, but i would find it hard to believe they are wrong as much as you say.
When they say something is confirmed you have watched them do it, what incentive do they have to fake it, their profits don’t depend on a confirmed to busted ratio
Mind you for some of the busted things, there may be a different way that would work or it could be a one in a million result, those can happen but not show up in their tests, hence the broad range conclusions may not always be accurate