Car still burning antifreeze

The computer of the car is not responding, so the mechanic recommend me to change it, I need to know if i can check if the computer is working before replacing it. Also the prior problem was, that i had a cooler tempeture connection or something like that old, that was avoiding the fan to turn on. The problem now is that the antifreeze is still very hot, the fun works but it it wasting the antifreeze 'til a point when i run out of it. I'm going to change the thermostat too, just in case.

So, what do you recommend to do about it?
How can i check if the computer doesn't work?
should i change the Thermostat?

I have a olds cuttlas ciera 90 3.3l
I have a previous threat about the same.

Thank you guys, you are amazingly helpfull