i have a 86 gxl and the temp gauge goes up more than half way some times but only some times when you run the car kind of hard or high rpms what might be the problem it was doing this for a while then went away then just came back i think it might be the thermostat any ideas what it might be

 

mine did that till i replaced the thermostat....now it stays at 1/4 way and mabey crawls close to 1/2 going hard or going up hill....but never tries to go over anymore.... makesure you get a mazda replacement.... or an after market one with a breather hole in the thermostant