You can tell a lot about your car's automatic transmission simply by looking at the color of its fluid. Here's a quick primer on how to deduce your transmission's overall health with just a quick fluid check.

Bright Red

Crack open a bottle of transmission fluid, and remember how it looks now because this is how it'll look when it's fresh and new. Once it goes inside your transmission, however, the combination of heat and wear will cause it to take on a darker hue as time goes on.

The vast majority of transmission fluid is dyed bright red to help distinguish it from other fluids in your vehicle. Keep in mind that some varieties of ATF can be dyed differently for a variety of reasons. The exceptions often include fluids used on certain imports and aftermarket performance fluids.

Cherry Red or Dark Red

After spending a few miles inside your transmission, the fluid will slowly transition from its original bright red color to a slightly darker hue. How dark your transmission fluid gets depends on the amount of wear it's subjected to, as well as the amount of heat it dissipates.

Check the dipstick after you have driven a few thousand miles since the last change. You can expect the transmission fluid to have a cherry-red or maroon-ish color without any signs of metal flakes or strange odors. This is how healthy transmission fluid is supposed to look.

Very Dark Red or Brownish

Transmission fluid gets progressively darker as the lubricants, dyes, friction modifiers, and various other additives wear out with use. As the fluid reaches the end of its usable lifespan, it'll take on a very dark red or even brownish hue. Seeing extremely dark transmission fluid shouldn't be a cause for alarm as long as the transmission itself shifts properly. However, it is a sign that the fluid needs changing as soon as possible.

Following your vehicle manufacturer's recommendations on fluid changes can help you avoid the worries that come with dark transmission fluid. Manufacturers may recommend fluid changes as early as 30,000 miles or as late as 100,000 miles, depending on transmission type and the level of usage.

Black

If your transmission fluid looks pitch black, you definitely have a problem on your hands. Using worn transmission fluid well past its change-by mileage can have harmful consequences. Slipping clutch bands and worn gears are common results of transmission fluid with little to no lubricating properties left. Metal-on-metal friction also increases internal temperatures, making your transmission too hot for the fluid to handle.

Once the transmission fluid gets to this point, there's no turning back. A simple drain and fill won't do much for your transmission's health, and it can even make it perform worse. Only extensive service can help undo the damage that's been done.

Pink or Extremely Light Red

When water or antifreeze mixes with transmission fluid, the end result is often a pinkish, foaming mess. This usually happens when engine coolant leaks through the transmission cooler integrated into the radiator. Transmissions can also pick up water when driving through flooded areas.

Take your car to an auto transmission service for more information.