Automatic Transmission Fluid: Caring for Your Automatic Transmission

The transmission is one of the hardest working systems and one of the most expensive to replace if it fails. Symptoms of an issue with your transmission include: slipping, hesitation, bucking, grinding gears and difficulty shifting.

According to ATRA, 90% of ALL transmission failures are caused by overheating. Most of these can be blamed on worn out transmission fluid. At elevated operating temperatures, Automatic Transmission Fluid oxidizes, turns brown and smells like burnt toast. Heat destroys the fluid's lubricating qualities and friction characteristics, varnish forms on internal parts which interferes with the operation of the transmission. At higher temperatures the transmission begins to slip and rubber seals harden, which lead to leaks and pressure losses. Any number of things can push automatic transmission fluid temperatures beyond the system's ability to maintain safe limits: towing a trailer, mountain driving, driving at sustained high speeds during hot weather, stop-and-go driving in city traffic, "rocking" an automatic transmission from drive to reverse to free a tire from mud or snow, etc. Problems in the engine cooling system itself will diminish automatic transmission fluid cooling efficiency since the cooling systems are interconnected.

Most vehicle owner's manuals do not specify a change interval for automatic transmission fluid, unless the vehicle is used for towing. The vehicle manufacturers say their fluids can go upwards of 100,000 miles under normal driving conditions. Yet most transmission experts say regular transmission fluid flushes and filter changes every 25,000 to 30,000 miles or every 2 years can significantly prolong the life of the transmission. As a rule of thumb every 20 degree increase in operating temperature above 175 degrees F. cuts the life of the fluid in half!

For most vehicles, checking the automatic transmission fluid consists of pulling the transmission dipstick out while the engine is warmed up and running and with the transmission in park. We suggest that you check your owner's manual, however, since some manufacturers may have a different procedure. Of course, always check your fluid level if you notice a leak of any kind. However, unlike engine oil, automatic transmission fluid doesn't burn up. So if you're low on transmission fluid, you almost certainly have a leak. When refilling automatic transmission fluid use the type specified in your owner's manual or printed on the transmission dipstick.

CAUTION: Do not overfill the transmission. Too much fluid can cause the fluid to foam, which in turn can lead to erratic shifting, oil starvation and transmission damage. Too much fluid may also force automatic transmission fluid to leak past the transmission seals.

Automatic Transmission Rebuilders Assoc. recommends these tips to help reduce heat, and keep your transmission working longer:

1. Avoid Jackrabbit Starts

2. Help the Shift — just before the shift; back off on the gas just a bit

3. Keep the Cooling System in Good Shape

4. Add a Transmission Cooler — especially if you travel a lot in extremely high temperatures or carry heavy loads.