Could be from damaged or misplaced o-rings in the tank. Could be a difference in air temperature or a difference in air pressure when going from a hot to cool area, or vice versa. You may have crossthreaded the coil or crossthreaded the top or bottom of the tank during assembly. See the last two items in the troubleshooting/tips below:
crossthreading
Have you been able to determine the specific location on the tank the leaking is coming from?
Clearomizer Troubleshooting and Tips:
"Flooding" is a common occurrence in e-cigarettes. The definition of flooding is getting juice into the air passage of the tank. This can include any point between the mouth piece and the very bottom part that connects to the battery. Each tank has holes in that air passage, where the wicks passthrough. This is required for the device to work properly. Unfortunately, this opens up the possibility for flooding. The trick with flooding, is knowing how to avoid it. I’ll explain a little more, but a few common causes for flooding a tank include: improper filling, over filling, pulling too hard when hitting the device, and the temperature can even play a role and/or damage.
"Dry" or "burnt" hits are also a common occurrence in e-cigarettes. This happens when an inadequate quantity of e-liquid reaches the coil. This can occur from using an e-liquid which is too thick for a tank, intake holes for the e-liquid being inadequate, or using a bad wick or coil. Doing "primer puffs", which is taking a puff or two without power on, may eliminate this phenomenon.
Before I get into the explanation, let me explain how an e-cig works a little more in depth. Nearly every tank has a wick that is used to absorb the juice in the tank. This wick cuts through the air passage. Each wick has a piece of wire that wraps around it in a coil. When you activate the button on the battery, you send electricity through the wire. As the wire heats up, it vaporizes the juice that is in the wick.
Improper Filling: When filling your tank, you have to be careful not to get juice into the center tube of the tank. This center tube is the air passage. When you take a draw, air comes from the bottom of the tank, through the air passage and into your mouth. If you get juice into this passage way, your tank is flooded.
Over Filling: If you over fill a tank (specifically a top coil like the ones that come with the starter kits and gift boxes), the wicks can become over saturated and just like a rain cloud, they will leak into the air passage. Once this happens, you have a flooded tank.
Pulling Too Hard: As I mentioned the wicks absorb the juice in the tank. As you pull on the device, you cause a vacuum effect that pulls juice into the wicks. If you pull too hard, you can pull in more juice then the coil can vaporize. If this happens, the juice leaks into the air passage and you have a flooded tank.
Temperature: E-Juice is a viscous liquid. Which means that as it warms up, it will thin out. And in the opposite form, it will thicken when it gets cold. When it thins, it is more difficult for the wicks to hold back the thin juice. This usually causes the wicks to over saturate and, you guessed it, it will leak into the air passage and you have a flooded tank.
Damage: There are o-rings and gaskets used that can wear out with usage. If certain ones fail or get lost, leaking will occur, in turn flooding the air passage and causing you to have a flooded tank. Other than accidentally losing something, damage can occur when its carried in a purse or a pocket or by over tightening the tank to the battery. Over tightening is a very common cause of leaking due to the damage it creates.
Why does my Tank Leak and what can I do about it? | E-Cigarette Forum
