Mazda 323 Problem Report
Mazda 323 Transmission Shifts In and Out of Overdrive
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.