Making Automatic Transmissions Last

With today's automobile engines lasting 200,000 - 300,000 miles or more when properly serviced, how come so many transmissions are still dying early in the game?

It's estimated that over 13 million automatic transmissions fail every year, and $2,000 or more for repair is not unusual.

Automatic Transmission

In the interest of curbing air pollution and increasing efficiency and fuel mileage, the transmission has been downsized from the cars 40 years ago and is in the engine compartment where there is more heat and wind tunnel-designed bodies reduce air flow over the transmission.

The Automatic Transmission Rebuilders Association estimates a high percentage of transmission failures are due to transmission and transmission fluid overheating. The oxidation rate (which determines the useful lubrication life) of automatic transmission fluid doubles for every 20 degrees F. temperature increase over the normal operating level. This means fluid that's formulated to last 100,000 miles at 175 degrees F. will only go 50,000 at 195 degrees F., or a mere 3,000 miles at 275 degrees F. Oxidized transmission fluid does not lubricate the transmission properly, causes seals to harden and leads to early failure.

Regular servicing of the transmission can extend your Automatic Transmission's life dramatically. The recommend servicing interval for the type of driving normally encountered by the average driver is every 30,000 miles with standard fluid and 60,000 - 100,000 miles with long-life fluid. Vehicles that do excessive stop and go driving or towing should be serviced more often.

Improved fluids have allowed service intervals to extend for many vehicles with automatic transmissions, utilizing “lifetime fluids.” In the past, service recommendations for automatic transmissions were based on time/mileage tied to requirements of new vehicle warranties (2-3 years or 30,000 miles). Lifetime fluid recommendations are now 5-10 years or the life of the vehicle (100,000 miles) unless the vehicle is subjected to "severe duty".

But what is severe duty? Taken directly from OEM owner's manuals, severe duty has historically been defined as:

Operation of vehicle when ambient temperature is above 100F or below 0F.
Carrying heavy loads or multiple passengers on a daily basis.
High speed highway or interstate driving for extended periods of time.
Driving in hilly or mountainous areas.
Stop and go driving.
By definition, most drivers are engaged in severe duty vehicle operation most of the time.

Transmission Flushing

If the tranmsisson is serviced regularily, flushing is not usually necessary, once the transmission fluid becomes oxidized or burnt though, a flush is recommended, since under normal servicing, only about 50% of the fluid can be drained out.

Transmission coolers are also recommended for any vehicle towing often or anytime towing heavy loads.

Most manufactures now have special fluids for their transmissions that differ from make to make. While there are universal fluids out there, they may not perform as well as the manufactures specified fluid and may cause shifting problems or eventual transmission failure.

Because of damage caused by incorrect fluids being put in their automatic transmissions, many manufactures have removed the dipstick/filler tubes from newer cars and trucks, requiring special procedures to check fluid levels and add fluid.


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