That's not good, your killing your HDD by doing that. less lifetime expectancy. higher temperatures. higher chance of data corruption due to high temps, if the drive gets too hot it will shut down don't think it won't because it will. your better off using a usb 3.0 dock that supports 2.5"/3.5" HDD's and using a 7200 RPM HDD with a 64MB Cache
My harddrive never overheats. It's an old 160GB from a TX1000 HP laptop that fried it's graphics chip. I stuffed it (with it's USB interface board) into an old DMG Gameboy for aesthetic purposes, and also to give it some breathing room. Runs flawless, and always stays cool. And My USB 3.0 dock accepts both harddrive sizes, but it will only run at 2.0 speed, so the 7200 RPM harddrive seems useless since it won't read data any faster than say, 30MB/s at any given time. 5400RPM does the job just fine, and without the excess noise, vibration, power draw, and heat.