Automatic Transmission Fluid
Automatic transmission fluid is either a highly refined mineral oil or a newer synthetic. The manufacturers add detergents and other compounds to reduce oxidation, foaming, and other general wear concerns. Transmission fluid lasts much longer than engine oil because engine oil suffers from the residue created in the engines combustion chamber.
For the older vehicles transmission fluid should be changed every 30,000 miles while some of the newer vehicles every 100,000. The fluids life depends upon the several factors:
Type of Fluid: Fluids offer different levels of protection: surfactants, anti- oxidation compounds, detergents, anti-foam additives, and anti-wear additives, friction modifiers and such are added to help protect and add life to the transmission.
Type of Transmission: Older designs require fluids that won’t last as long as the newer type that use the DEXRON lll and MERCON fluids. Some vehicles use a screen-type filter designed to catch the larger debris while leaving the smaller particles to circulate with the fluid. The good thing is a screen type filter can be cleaned and reused the bad is the cloth type does a better job of cleaning. Ideally transmission fluid should be flushed every 2 years or 24,000 miles.
Temperature: Transmission fluids ability to withstand temperate depends on its design. Typically ATF is designed to operate at 175° F. Transmission fluid breaks down quickly as it exceeds this temperature. Remember a 20° F increase in temperature will decrease the fluids life by half.
Transmission fluid breakdown is the result of heat generated by the torque converter, debris caused by friction surfaces on the bands and clutch packs, and just normal wear. If the transmission fluid appears milky check for contamination. The transmission fluid can mix with the coolant in the transmission cooler giving it a pink milky appearance.
When fluid level is low the transmission will slip and have a delayed engagement. When fluid levels are high the fluid becomes sudsy and aerated. Aerated transmission fluid will cause noise and slippage. It’s vital to check and keep the transmission fluid at the correct level.
Discolored fluid is a sign of overheating and oxidation. Transmission fluid is red in color and begins to turn brown and then black. Discolored transmission fluid requires a transmission flush to completely remove the fluid from the transmission. A transmission drain and fill can leave much of the oxidized fluid still in the case.
