people

my e30 ´s been having problems due to a stupid mechanic which does not know about e30.
anyway... the issue.
My heat indicator usually was showing before the half let´s say (1/4 or so)
now is showing on the (1/2).
It goes to that point after a couple of miles driving and it stays there.
I feel the car a little bit warmer than normal tho.
All this happens after my ´´mechanic´´ did the replacement of the timing belt and the valve adjustment.
please advise the following:
-when do you usually get to the (1/2) of the heat indicator after start driving.
-what is the normal tempeture for one of this engines?
-could it be the thermostat misfiring?
Another thing that is happening is that the water is getting hot, and the cool water sensor turns the light on at least once a week, the tank is still full of water tho.
Please advise me is very important for me.
JT
my engine is 320i (2000 cc)L-JETRONIC fuel injection, chassis e30, year 1985, production date is 09/84.