The only change I've noticed with a well-used coil is that the taste starts to go off a little bit, and that's usually after weeks of steady use. In fact, whenever I put a new coil in, there is a noticeable increase in power, so I don't know why you're getting more heat with an older coil. Hopefully, smarter guys/gals than me (which means all of them) will be able to help you more.