If the automatic transmission shifts in and out of overdrive while cruising, it may be due to the thermostat that is stuck open. The 323 transmission is especially effected by the engine running too cool. If possible, check to see the engine is running at full operating temperature while cruising. The temperature gauge in the 323 may also read normal when the engine is not reaching normal operating temperature.
Car Problem Reports
Mazda 323 Transmission Shifts In and Out of Overdrive
Mazda 323 Problem
the light for the over drive keeps going on and off and it seems that the car is very heavy
Visitor, 1990 Mazda 323, 77,000 mi
During the winter, the car will sometimes lock the torque converter, but then release it. Stays in top gear, but you can tell it isn't locked by varying the throttle pressure and watching the tach. Temp is running at 170, but will try a higher temp thermostat. Mine is a mercury capri, but same engine/tranny