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An automatic transmission is second only to the engine as the most complex and costly mechanical component on your car. To work properly, an automatic transmission must be filled with a specific fluid that is maintained at a precise level. Automatic transmission fluids serve many purposes. They transmit power, operate hydraulic systems, provide lubrication, keep seals soft, protect internal transmission components and act as coolants. To preserve these capabilities, the automatic transmission fluid level should be checked regularly, and the fluid may need to be replaced periodically at intervals recommended by the vehicle manufacturer.

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Modern automatic transmission fluids are carefully formulated chemical compounds and are often developed for specific transmission designs. While some companies market “universal” transmission fluids, most vehicle manufacturers have proprietary specifications for the fluids used in their automatic transmissions. Failure to use the proper fluid can affect shift quality, reduce transmission life and may void your car’s warranty. When topping up or changing transmission fluid, make sure the product used by the auto repair shop meets the requirements stated in your owner’s manual.

Automatic transmissions have become marvels of precision and durability in recent years. Many late-model cars use synthetic “lifetime” transmission fluids and have sealed transmissions without a dipstick to check the fluid level. As long as the transmission has no leaks, the fluid will remain at the proper level. Even some cars with dipsticks use "lifetime" fluids that either never need changing, or are changed only at extended intervals that can exceed 100,000 miles.

Checking the transmission fluid level

On vehicles that have dipsticks, the automatic transmission fluid level should be checked monthly with the transmission at full operating temperature and the engine idling. Around 15 minutes of driving is typically required to fully warm up the transmission. You can check the fluid level in six easy steps:

    1. Stop the vehicle on a level surface, apply the parking brake and allow the engine to idle.

    2. Apply the brake pedal and move the gear selector through all gear positions, pausing for a few seconds in each. Then, place the transmission in park or neutral as specified in your owner’s manual.

    3. Open the hood, locate the transmission dipstick and carefully remove it making sure to avoid any hot or moving engine parts.

    4. Wipe the dipstick clean with a rag, and note the level markings near its end. Some dipsticks have one mark for FULL and another for ADD, some have small holes that indicate the maximum and minimum oil levels, and some have crosshatch markings to designate the acceptable fluid range.

    5. Insert the dipstick fully back into its tube, then remove it and read the level.

    6. If the fluid level is at or below the ADD mark, add enough fluid to bring the level up to the FULL mark. Do not overfill. Typically, the distance between the ADD and FULL marks is equal to one pint of fluid.

When checking the fluid level, also inspect its color. New automatic transmission fluid has a red or pink tint. Fluid that is reddish-amber to medium brown has been in service for some time, but a color change of this type is normal and not a cause for immediate fluid replacement. However, a dark brown or black color is a sign of deteriorated fluid that needs to be changed. Fluids that have a milky appearance, or smell burnt, indicate more serious transmission problems that call for diagnosis by a qualified auto mechanic as soon as possible.

Changing the transmission fluid

As already mentioned, many newer cars never need transmission fluid changes, or changes are required only at extended intervals. However, millions of cars on the road still need regular transmission fluid replacement. The recommended intervals for this service will vary, depending on the car’s factory maintenance schedule and whether the vehicle is used in normal or severe service. In some cases, the transmission contains a filter that is changed at the same time as the fluid. Consult your owner’s manual to identify the intervals appropriate for your car and the type of driving you do.

When having the transmission fluid changed, make sure the auto repair shop uses a replacement fluid that meets the automaker’s specifications. It is also very important that the transmission not be overfilled, as this will cause fluid foaming that can lead to other transmission problems.

Finding Quality Auto Repair

AAA recommends that you plan ahead for vehicle service by finding an auto repair shop and technician you can trust before you need them. provides information on nearly 7,000 Approved Auto Repair facilities that have met AAA’s high standards for appearance, technician training and certification, insurance coverage and customer satisfaction. AAA regularly inspects every Approved Auto Repair facility and surveys their customers to ensure ongoing performance. In addition, AAA members receive special benefits that include auto repair discounts, an extended 24-month/24,000-mile parts and labor warranty, and AAA assistance in resolving repair-related issues.

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