[dougmcp]

Yes I'm sure. The solenoids that you see welded shut, and there are many, are from years of making and breaking of the contacts under a high current load which causes them to arc, get rough and then stick closed (on position). The reason for this is that the spring is not strong enough to release the contact or it is fact welded closed.

Operating at a higher voltage, given the same power requirement in wattage will require less amperage and therefore less wear on the contacts with an end result in less sticking. 48v applied to a 36v coil is a little tough on it but in actuality the contacts close faster and have less arcing than it would have at 36v. The spring solenoid release is set so there is no difference between 36v and 48v.

Regarding the actuation portion of the solenoid, the disadvantage to running a 36v coil on 48v is that you are overdriving it by 20% and the coil could fail leaving you with a solenoid stuck in the off/open position.

This is just the theory portion of it.
Usually people who upgrade to a higher voltage also run them harder and demand more amperage from them which can create the sticking problem.

You have tons of experience with these and we all know sh*t happens all the time to these carts for reasons no one can seem to explain.

Just for clarification, a solenoid (actually a contactor) has 2 parts, the actuation coil and the contacts.
When a solenoid is welded, it is the contacts stuck together, considered "closed" or "on".
When the coil is burned out it is considered "open" because it cannot actuate and close the contacts.