I have a 2006 toyota camry, automatic, 4Cyl, 120K miles. I guess (because it's a used car) the previous owner never changed the automatic transmission fluid before. Google online these days, it seems like change automatic transmission fluid on a high mileage car would potentially damage the car. What do you think?

 

Just have the fluid changed/exchanged for new fluid. This means not doing a flush, power flush, back flush, using no compressed air and using no cleaning chemicals.

The best fluid changing machines uses the transmissions own oil pump. The old fluid is pumped out with engine running from a disconnected oil cooler return line from the radiator. This while new fluid is added to the trans at the same rate. When exiting fluid is clear, the job is done.

Have the trans pan cleaned and filter changed at the same time.

 

drain the refill today, one more question is I refill with 4qt new fluid and but it seems like the fluid level is still below the dipstick hot minimum. I checked it when the car is hot.
Any idea?

 

I guess I overfilled the ATF, how can I pull it out? What's the worst case of it if it's overfilled?

 

Get the trans fluid up to normal operating temp. Engine running, move gear selector from Park to Low and back to Park pausing in each gear. Engine running check trans fluid level. Wipe dipstick to accurately check level mark. .

Excess fluid foams up causing oil starvation, trans slippage, heated oil, blown trans seals and then trans damage.