Car Engine and Other Systems - Maintain your transmission
Change automatic transmission fluid and filter after the first 5,000 miles (8,000 km) and after every 25,000 miles (40,000 km) or two years thereafter, or as recommended in your owner's manual. If you use your vehicle for towing, change the fluid and filter every year. For manual transmissions, change the lubricant (motor oil or gear oil, depending on the car) after the first 5,000 miles and after every 50,000 (80,000 km) thereafter. Use synthetic motor oil or gear lube for longer transmission life unless the manufacturer recommends otherwise.