Originally Posted by
mike_s
Never use WD-40 on a lock. Don't use oil on a lock. Either might help for a short time, but will only gum up/collect dirt over time and make things even worse. Flush it out with alcohol to get any dirt out, then use a dry lubricant made for locks, such as Lock-Ease (an alcohol/graphite mix - the alcohol carries the graphite, then evaporates, leaving only dry graphite).
This is bad advice more suited to the brass cylinder of a door lock than a U-lock out in the weather.
First of all the internal mechanism is steel and vulnerable to rust, and secondly water will weep into a dry lock. If you use it in freezing conditions water will freeze and jam the lock.
The goal is to provide a light lubrication of the mechanism and keep water out.
You can achieve these objectives using a very light oil/paraffin/solvent product like LPS-1, Boeshield, Frame saver, WD-40, or a homebrew mix of about 1:6 light oil:mineral spirits.