Now, back to the origonal quest in, heat and cold damage.
Yes, heat will damage fountain pens. Typical damage is a change of shape, such that the pen looks bent in the manner of a banana. This has never happened to a pen I have owned while I owned it, but I have both been given pens that were misshapen in this manner and I have purchased pens that were misshapen in this manner for parts as the nibs in both cases were undamaged and in good condition.
Yes, cold will damage fountain pens. I have had this happen to a fountain pen I have owned, a Parker 45. I left it in my car for a few weeks in very cold weather, well below freezing, and the upper barrel, the part which fit under the cap became misshapen such that there is an indentation completely around part of the barrel which matches where the cap constricted the plastic. I have seen this on several other Parker 45s. The pen otherwise is fine. I have not attempted this with other pens.
I have also had one pen start to fall apart while in a climate controlled environment, an early Sheaffer balance in a color known to do this. Thankfully it didn't effect any of the other pens in the case it was in and the damage was limited to the cap edge, which may have also been subject to stress repeatedly for years prior to my getting it and led to it literally starting to crumble while not under stress, simply siting in a case. Other pens are also known for having this problem, including some Sheaffer balance 2s in some colors, so it may be a design flaw long standing which coupled to certain inferior materials results in that failure. There are many other pens made by other manufacturers in many different eras which are known to fail in this manner. I don't know if heat and cold makes it worse. Storage in a non breathable environment which does not allow for out gassing supposedly does.
Edited by Parker51, 10 April 2020 - 18:22.