temp/cooling sys. please read need help! on 1991 BMW 735i

this car was well taken care of and i drove to work the other day and smoked a cig.w/ac on, as always, and bofore i was done it was dinging saying coolant temp. so i shut off car and waited 2hrs. Then tried to add water but was full. So drove to the store and back and the upper hose on radiator was still squeezable after warmed up .... should it be or is the thermostat sticking. today it went above half but back below half once i started moving and never did before. owned car for 10 months thanks

There is a burping valve on the thermostat( a 8mill bolt that sticks out of the top of themostat). When topping off always open the burping valve untill h2o or coolent flows out. Tighten up bolt, but keep resivor cap off and start car. Once 735I is at running temp open burp valve if only fluid runs out, without presureized air spray. Close it up and top off resivor and tighten up lid. If there is still air in system keep filling and burping untill air is gone.
Don't fill resivor to top while motor is cold. This can potentailly split resivor if overflow is cloogged or nonopp.

Good luck
I would change the thermostat, fan and coolant temp sensor with the coolant and if you have a cap change also plus bleed the air as said and you should be on your way> I will mention do not ever use water in that car again only antifreeze / coolant and when ever you are interested in selling call me just send me a pic of vehicle 3476865031
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Have your radiator cap, viscous and thermo electric fan and water pump checked.