1997 Chevrolet Astro Owner's Manual - Page 276

Automatic TransmissionFluid When to Check and Change A good time to check your automatic transmission fluid level is when the engine oil is changed. If you do it yourself, be sure to follow all the instructions here, or you could get a false reading on the dipstick. NOTICE: Too much or too little fluid can damage your transmission. Too much can mean that some of the fluid could come out and fall hot engine on parts or exhaust system parts, starting a fire. Be sure to get an accurate reading if you check your transmission fluid. Change both the fluid and filter every 15,000 miles (25 000 km) if the vehicle is mainly driven under one or more of these conditions: 0 In heavy city traffic where the outside temperature regularly reaches 90 O F (32 " C ) or higher. In hilly or mountainous terrain. 0 ~ When doing frequent trailer towing. Uses such as found in taxi, police or delivery service. Wait at least 30 minutes before checking the transmission fluid level if you have been driving: 0 0 0 0 If you do not use your vehicle under any of these conditions, change the fluid and filter every 30,000 miles (50 000 km). See "Scheduled Maintenance Services" in the Index. When outside temperatures are above 90°F (32°C). At high speed for quite a while. In heavy traffic -- especially in hot weather. How to Check Because this operation can be a little difficult, you may choose to have this done at your GM dealership Service Department. While pulling a trailer. To get the right reading, the fluid should be at normal operating temperature, which is 180°F to 200°F (82°C to 93°C). 6-20