Metal gate in hot weather

More than likely, the column of blocks has settled slightly causing your problem. I can't see from your picture, but has the gap between the top blocks and wall also opened slightly? If it has, then your blocks have shifted. Usually the weight of a large gate, such as you have, causes this problem on a fairly new install, especially since you only have a one block column.

My suggestion would be to add some "L" bracket supports or other mounting directly to the wall and column. Use your imagination and I'm sure you can find or make something that would look nice with the finish of the wall and blocks. Whatever you use, be sure to mount it to the block first, flush to the finished edge. Then screw or lag it into a good solid point of the wall (stud or plate) in order to use the mechanical advantage to pull the column, close the gap and restore the column to the original plumb-line, or at least stop any additional settling and tilting. Mounting the brackets to the same block the gate hinges are mounted to would help support the weight of the gate and not stress the mortar joints of the rest of the column. Be sure to consider sealing any devices you may have to install in the wall to prevent any water from entering. If you end up needing to use some ugly but strong utility type brackets, you could build a nice looking small valance box covering and stucco it to match. Lots of decorating alternatives.

The bottom line is to devise a way to attach the sides or top of the column firmly to the building and stop the settling from getting worse and making your nice gate inoperative.

To me, it looks like you have a very old Zinc coated gate, which has many areas which have been touched up with a grey paint (I may be completely wrong)..

Typically the galvanization is done when the clean metal fence is dipped into molten zinc and effectively coated in a corrosive resistant zinc shell. if you would like to return the fence to original condition, your best bet would be to remove the entire gate and take the unit to a galvanizing plant for re-galvanizing. Unfortunately the fact that it may already be galvanized means that they need to acid remove the original coating which will cost double, and they would be worried that the acid burns into the mesh too much. (you would have to remove your lock and consult the galvanizing guys if the current hinges will be ok)

The other option is to simply remove all traces of the rust from the existing gate and re-apply a coating of paint. I would say if you choose to paint the gate do not remove, however if spraying is your intention, then i would recommend removal.

To prepare for painting. some sand paper and stainless steel brushes would do the trick, if you have some power tools you could really benefit from steel brush powertool accessories (drill, grinder or polisher)

Using some sand paper, and steel brushes (in the heavy rust areas) scrape away all rust. Once you are happy, I would apply a primer coating (zinc chromite metal primer) and then a final coat of good quality enamel paint.

The corrosion you are seeing are the zinc which has formed pots (are you near the coast?) if so... painting your fence with enamel is not advised.. since corrosion is too excessive near the coast.

another option would be to prepare the fence (sanding where the rust areas are) and then re-applying the galvanized coating with a brush. this will add some life back to the gate (but does not compare to actually having the gate professionally galvanized)

a Google search for galvanizing paint or spray should get some results.

Lastly, if you are worried about painting on the wall, simply use some masking tape on the edges.