Transmission fluid does wear out. New fluid has a pink color to it and the old fluid will appear brown and emit a slight burnt smell. The color and smell are from the normal wear of the many clutch discs located in the heart of a transmission.
Heat is the worst thing for transmission fluid—even the relatively mild temperatures here in good old Overland Park, Kansas, can cause problems. Elevated temperatures cause the fluid to lose its ability to withstand pressure when and where needed inside the transmission. This is why you find additional external coolers on many trucks and SUVs.
Transmissions are mostly all built with the same fundamental concepts, and automatic transmission fluid (ATF) is manufactured by fewer petroleum companies than one would think. ATF base stock is much the same—it is the additives that make the final difference. With that in mind, we recommend flushing an automatic transmission every 30,000 miles for best life and performance. Many transmission rebuilding companies recommend flushing on a frequent basis, since they constantly see the results of lack of maintenance.
The flushing procedure is like a blood transfusion. Fluid is pumped in one end and pulled out the other with a special machine. The fluid level is also critical and must be set at operating temperature. Too much fluid causes it to aerate or foam up, and too little will cause slipping, leading to excess heat.
Do-it-yourselfers are finding that many newer transmissions are sealed with no dipstick, so there is no easy way to check the level or even fill it back up.
The bottom line is this: an automatic transmission will easily last more than 200,000 miles if maintained periodically. Replacing one can cost thousands of dollars. It is easy to do the math. You can count on us to stay on top of changes in transmissions and their maintenance requirements.