Automatic Transmission Fluid
The next time you check the fluid level in an automatic, sniff the fluid on the end of the dip stick. If it smells like burned toast and/or has a discolored brown appearance, the fluid has cooked itself and is no longer capable of providing proper lubrication to the transmission. If you’re lucky, you may have caught the problem before serious damage has been done — but more often than not by the time the fried fluid is discovered, the transmission is also toast.
Compared to motor oil, ATF has live pretty easy. There’s no soot, gasoline or condensation from combustion blowby to contaminate the fluid. The only physical contaminants the fluid must deal with are particles that wear off the friction plates, gears and bearings inside the transmission. Most transmissions have some type of internal filter to keep the fluid clean. Some do a pretty good job, but others don’t. Most Asian transmissions only have a plastic or metal strainer that can only trap the larger pieces of debris. The rest circulates with the fluid and accelerates wear. Changing the fluid is the only way to get rid of these contaminants.
Heat is the main concern for ATF. Automatic transmissions create a lot of friction, and friction produces heat. The fluid is constantly churning inside the torque converter and being pumped through metering orifices and hydraulic circuits. Every time the transmission shifts gears, the clutch packs generate even more heat that must be carried away by the fluid. The greater the load on the transmission, the more heat it generates and the hotter the fluid gets. Most ATF can withstand normal operating temperatures of around 200 degrees F for tens of thousands of miles. But if the temperature of the fluid rises above 220 degrees F the fluid starts to break down quickly. Above 300 degrees, fluid life is measured in hundreds, not thousands of miles. And above 400 degrees, the fluid can self- destruct in 20 to 30 minutes!
ATF contains ingredients to improve its oxidation stability as well as other additives to reduce foaming and inhibit corrosion. Over time, the protective additives can also break down causing the fluid’s lubrication properties and viscosity to change for the worse. That’s why fluid breakdown is the leading cause of transmission operating problems and failure. Most experts still recommend changing the fluid and filter every 2 to 3 years or 24,000 to 36,000 miles — or once a year or every 15,000 miles if a vehicle is used for towing or other severe service use.
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