How warm is the room where the fishtank is? Keep it as far away from the heater/vents... Maybe move the tank a bit closer to the window (without putting it in direct sunlight)?
Do you think there's enough holes in the top for excess heat to escape?
I'm no newt expert, but I've played with my tank a TON to finally establish a happy temp.
I hopped around online and found this article. I dunno if it'll help, but may be a starting point.
http://exoticpets.about.com/cs/salam...liednewt_2.htm