Be aware that longevity decreases with lower temperatures unlike the opposite preconception common these days. The longest lifespan occurs if the drives are kept at around 40C.
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Google has a large amount of disks and data to support this and they were the ones who showed that preconception to be false. Google have implemented heated cabinets to increase the longevity of their disks.
Yes, my guess on that was that drives are designed for a specific tolerance window of physical expansion and contraction due to temperature changes (and corresponding air pressure), and it's uncommon for drives to be below room temperature. On a related note, you haven't seen this, it's an interesting read about how precisely drives are manufactured and assembled:
http://www.overclock.net/t/1312694/information-as-to-why-not-to-open-a-hard-drive-to-repair-it"In the past I have seen users ask about opening drives to attempt to do a platter swap and whatnot, but that is not a feasible thing to do. Let me just go through a few things here as to why you should NEVER open a drive on your own and attempt a "fix".
Just the seemingly simple act of removing the cover on the drive will cause it to no longer work properly. The reason being is that each and every one of the screws on the cover have a specific torgue that they MUST be tightened with. The top cover with proper torque settings "set" the rest of the drive as the drive is calibrarted for the ever so slight warping of the casing caused by the torque from the screws on the cover!
Additionally dust is a HUGE concern. The heads that fly across the platters at 10000 Gs of acceleration are literally floating above the platters on a blanket of air caused by the platters spinning at 75MPH (7200RPM). These heads are just several 1000ths of an inch off the surface of the platter, so all it takes is a piece of dust to come along and it is hitting a car with a boulder. The platter and the heads can get damaged severely!
Along with the fact that the heads are "floating" across the plattters, they are also aligned within microns of where they have to be. Each drive has the heads aligned perfectly. Plus, you have to use a specific technique to get the heads back onto the platters if you remove the head stack and the heads have to be clean for proper functionality.
One last thing is the platters. They don't seem like much, but they are PERFECTLY aligned and tampering with the bolts that hold down the platters or even removing them can screw up the alignment of the platters. Not only are the aligned to be PERFECLY spaced (tolerances are within the 1000ths of an inch, if not less). Furthermore, they are also aligned so that the tracking information that is across all the platters are also perfect. If this is out of alignment even a hairs width, the data is in accessible as ALL the heads use this data to know where they are on the platters at all times. What this means is that platter swapping is COMLETELY out of the question, unless you got the equipment to realign the platters and tracking information (which differs from manufacture and even from drives from different manufacturing dates even though they are the same model). After that, realign the heads again (which differs from drive model and manufacturer and is a closely guided secret). If you do, then have fun. Then while you are at it, also re-write the firmware on the logic board so that it understands tracking information on the platters so it then knows how to modulation the voice coil to put the heads properly on the disk.
One last bit of trivia. You know that little hole on the drive that says "do not cover"? The drives operate to have the same air pressure as that on the outside and are not hermetically sealed. That is why when you go above 10000 feet you get head crashing and drive failure. There isn't enough air to float the heads across the platters.
This is a super simple down explaination. If you have questions, feel free to ask them here and I will answer them to the best of my ability.
TL;DR? DON'T OPEN HARD DRIVES!"
