Automatic Transmission Fluid

Transmission fluid check

Automatic transmission fluid is either a highly refined mineral oil or a newer synthetic blend. 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 residue created in the engine's combustion chamber. This does not occur in transmissions. The red-colored automatic transmission fluid turns brown from heat and oxidation.

For older vehicles, transmission fluid should be changed every 30,000 miles. With many late-model vehicles, a transmission fluid flush is recommended every 100,000 miles. The fluids life depends upon several factors:

Type of Fluid: Fluids offer different levels of protection. They contain surfactants, anti-oxidation compounds, detergents, anti-foam additives, anti-wear additives, and friction modifiers to help protect and add life to the transmission.

Debris in the Transmission Pan

Debris in an automatic transmission pan.

Transmission Service: Older transmissions require fluids that don't last as long as the newer designs. Some vehicles use a screen-type filter designed to catch the larger debris, leaving smaller particles circulating with the fluid. The good thing about a metal screen filter is that it can be cleaned and reused. The problem is the cloth screen does a better job of cleaning and picks up the smaller particles more efficiently. Ideally, transmission fluid should be flushed every two years or 24,000 miles.

Pink and Milky Transmission Fluid

Transmission Cooler

If the transmission fluid appears pink and milky, check for water contamination. The transmission cooler is located in the radiator. If there's a leak, transmission fluid, and coolant mix. This contamination results in pink milky transmission fluid.

Transmission Fluid Temperature

Transmission fluid's ability to withstand temperature depends on its design. Typically ATF is designed to operate at around 175┬░ F. It breaks down quickly as it exceeds this temperature. A 20┬░ F increase in temperature decreases the fluid's 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.

Transmission Fluid Level Check

Check the transmissions dipstick cold and hot.

When the fluid level is low, the transmission will slip and suffer delayed engagement. When fluid levels are high, the fluid becomes sudsy and aerated. Aerated transmission fluid causes noise and slippage. It's vital to check and keep the transmission fluid at the correct level.