The average automatic transmission is quite possibly one of the most complicated components on any vehicle. It also happens to the one of the most stressed components on the average vehicle, thanks in large part to the constant use and abuse it takes on a regular basis.

Dozens of mechanical, hydraulic and electronic components work together in harmony to smoothly and efficiently transfer power from the engine to the wheels. Keeping these components in great shape throughout the life of your vehicle means more than just checking the dipstick now and again – you’ve got to pay very close attention to the transmission fluid.

Automatic transmission cutaway
This cutaway of a Ford six speed automatic transmission shows just how complex a modern transmission can be. Image courtesy Ford Motor Company.

The transmission fluid is the lifeblood of any automatic transmission. Not only does it depend on the fluid’s lubrication properties to function properly, the fluid also transfers heat away from the transmission itself. When this fluid becomes worn out, it can easily spell disaster for any vehicle owner – is not unheard of for an automatic transmission to fail due to neglect.

When to Change Transmission Fluid

Most car owners know about the importance of changing their engine oil on time. On the other hand, most owners are clueless when it comes to knowing when to change their transmission fluid. Like engine oil, transmission fluid needs to be changed at regular intervals to ensure component longevity as well as performance and efficiency.

Conventional wisdom from most manufacturers dictates that drivers have their transmission fluid changed at 30,000-mile or two-year intervals. Some transmission fluids don’t have to be changed until the 100,000-mile mark or even greater. Of course, it’s a good idea to change the fluid at earlier intervals if the vehicle’s subject to any of the following conditions:

  • Towing
  • Hauling
  • Driving in constant stop-and-go traffic
  • Driving in severe heat or cold
  • Racing, sanctioned or not

When NOT to Change Transmission Fluid

Believe it or not, there is a certain point where changing the transmission fluid becomes more trouble than it’s worth. Knowing when to leave the transmission alone at a certain point can help squeeze in a little more life out of it while preparing for a major repair:

  1. The transmission fluid has a burnt odor. Aging transmission fluid can easily deteriorate under the extreme heat generated by the transmission itself. In most cases, the internal temperatures within an automatic transmission are up to 150 degrees higher than engine temperatures.
  2. The transmission fluid contains grit and debris. Finding metal debris in the transmission fluid is a definite sign of the major component that’s on its way out. That grit seen in old transmission fluid is actually bits of metal that has worn off the gears and clutches within the transmission.
  3. The fluid hasn’t been changed in over 100,000 miles. At this point, it’s better to plan ahead for a rebuild or replacement. Deliberate or accidental neglect of transmission fluid can easily cause one of the two above scenarios to occur.

Bottom Line: Knowing when to change transmission fluid can mean the difference between miles of carefree motoring and an expensive repair.

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