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Healthy transmission fluid will have glossy a reddish hue. If yours looks brown or black or has a distinct burnt odor, it’s probably time to replace it.

Your transmission fluid doesn’t need to be changed anywhere near as often as your engine oil. In newer cars, the recommended service interval may be as high as 100,000 miles (160,000 km). Consult your owner’s manual to find more concrete guidelines for the model you drive. [11]

This fluid is responsible for lubricating the transmission, or your car's gear system.

For best results, do this while the engine is running and fully warmed up (either in neutral or park, depending on the make and model). It will be the second of two dipsticks on the engine, usually colored red. As you did with the oil dipstick, pull it out, wipe it off, push it all the way back in, then slide it out again and check the level. Once again, look for the fluid to fall between the two notches, grooves, or marks on the dipstick.