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MotorLogic

Fluids

Transmission, brake and coolant service — including the ones called "lifetime".

Every fluid in a car except gasoline degrades by chemistry rather than by consumption. Brake fluid absorbs water. Coolant loses its corrosion inhibitors. Transmission fluid shears down and oxidizes. None of those changes show up on a dipstick until they are well advanced.

The phrase "filled for life" appears in a lot of modern owner's manuals, most often for automatic transmission fluid, and no manufacturer we could find defines what it means in miles or years. If you intend to keep the car past 150,000 miles, servicing the transmission fluid is one of the highest-return decisions available to you — and how often it is actually due is more contested than any source will admit.

Fluids services