How long does transmission fluid last?
The best guideline for when to change automatic transmission fluid comes from the manufacturer of the transmission itself. The owner’s manual for each vehicle provides the recommended mileage intervals for service. Typical recommendations generally range from 30,000 to 60,000 miles. Some manufacturers build transmissions which claim to have lifetime fluid, though when reading the fine print it’s usually decided that “lifetime” means about 100,000 miles. Never changing the fluid in the transmission is usually not a good idea, since the fluid breaks down as part of normal operation.
Many new style CVT (continuously variable transmission) and double clutch transmissions have very strict service guidelines, requiring the fluid to be changed every 30,000-40,000 miles, along with the filter.