What lubricant should I use for an outside garage door lock?
You'll want to use a dry silicone lubricant like this.



Or a graphite lubricant like this.



The liquid part of these lubricants evaporates quickly, leaving behind a protective coating that will keep the lock functioning properly for quite some time.

You don't want to use a lubricant like WD-40, because it will not evaporate completely and will collect dirt and debris and eventually freeze the lock again.

For an exterior lock exposed to the elements, you'll want to reapply the lubricant occasionally (about once every year or two depending on the weather), or anytime the lock seems sticky.