Hmmm... Maybe you got the lemon of the bunch, or I got the one good one out of the lot. I have mine set up on an outer wall also, but don't have any problems with temp spikes... And for the price, it works great for me. I got mine through reptilesupply.com for just over $20...

http://www.reptilesupply.com/product.php?products_id=75