getting speedometer to work on a 91 chev it is most likely the vehicle speed sensor on transaxle pass. side, about 40 dollars at part store
1991 Corsica its under the trottle body
For a 1991 Chevrolet Corsica : My Chilton's Auto Repair Manual shows : ( 15.6 U.S. gallons )
It doesn't have one, it is distributorless.
The speedometer is controlled by the speed sensor and it also sends signals to the transmission on when to shift so your problems could be related. The speed sensor is easy to replace and is located on the transmission.
13.6 gallons
You have to take the door apart
Green coolant (prestone, etc)
16.5 to 17.1 gal
Depends on which engine it has. Try a Google Search.
Broken cable?
Remove the wiring harness from the back of your 1991 Chevy Corsica turn signal. Remove the turn signal retaining bolts. The entire turn signal will come out. Reverse the process to install the new turn signal.
Need to figure out what's wrong with them, first.