Overheating?

Today out of the blue decelerating, coming of the highway, I noticed a tiny
bit of smoke coming out of the front drivers side hood. When I pulled over
and the car came to a stop the smoke increased and lasted for about 5
minutes before dissapating. There was a sizzling sound too, but that
stopped quickly as well. No engine light or any other apparent lights popped
on.However the electronics in this car are pretty messed up, lights often
come on for no reason, so there may be some that just don't come on?  I
attached a picture of where the temperature gage is, looks in ok, normal
range to me? The only other things I am considering ( in hindsight) are 1) I
have noticed a funny chemically burnt smell in the past month or so (leak?) 2
) The air conditioner has not been working as great as in the past. There was
coolant in the reservoir, but it was a little low so I added some water and
drove the 5 miles home slowly. No more smoke but I noticed the chemical
smell, again no lights went on.