Transmission Fluid Service

Why it matters

Automatic transmissions depend on fluid to transmit power, cool the internals, and keep clutch packs from slipping. Heat is what kills them: cooked fluid loses its friction properties and stops protecting the valves and solenoids that decide when you shift. A fluid service is one of the few inexpensive things you can do for a transmission.

Signs it is time

• Fluid is dark brown or smells burnt
• Shifts feel delayed, harsh, or flare between gears
• Slipping when you accelerate from a stop
• Fluid level low, or weeping around the pan
• Mileage past the interval in your manual, often 60,000 to 100,000 miles

If you wait

Contaminated fluid accelerates wear inside the transmission. Where a service costs a few hundred dollars, a rebuild or replacement runs into the thousands — and it is rarely worth it on an older car.