Im new to this as well but, the 15-20 days it stayed steady, was that before you added the eggs? Is it possible that the eggs themself could of raised the temp a degree or two? I'm not sure how early they start to build a little heat themself but I do remember reading at some point they do. Either way, i would think your best bet is just to drop your thermostat a degree or two and keep a close eye on your temps. If the temp stays consistent at the lower setting, then problem solved. Good luck with your clutch.