The Mercedes Benz E320, unlike most cars, does not come with transmission fluid dipsticks. For this reason, you must purchase one from a dealer or car parts store before checking and adding to your fluid levels. Once a dipstick is purchased, the process of adding and checking transmission fluid is identical to most other cars. Fluids should be checked once a week and changed every 30,000 miles to keep your Mercedes in good condition.
Turn you car on, allowing it to run for about 10 or 15 minutes to let the engine warm up.
Pop the bonnet of the car and locate the transmission cap. You will see a red cap behind the engine and near the transmission.
Unscrew the transmission cap. Insert the dipstick into the fluid well. Let it set for about 10 or 15 seconds.
Pull the dipstick out and check the readings. You will notice a line on bottom that says "LOW" and one on top that says "FULL". If fluid does not reach the "LOW" line, you will need to add more.
Pour transmission fluid directly into the hole where you unscrewed the cap. To recheck levels, wipe the dipstick clean with a rag and repeat the process. Once the fluid level is correct you may screw the cap back on and turn off your vehicle.