1999 Chevrolet Express Van Owner's Manual - Page 254

yellowblue D Uses such as found in taxi, police or delivery service. If your vehicle's GVWR is not over 8,600 and you do not use your vehicle under any of these conditions, change the fluid and filter every 100,000 miles (166 000 km). See "Scheduled Maintenance Services" in the Index. Wait at least 30 minutes before checking the transmission fluid level if you have been driving: How to Check Because this operation can be a little difficult, you may choose to have this done at the dealership service department. If you do it yourself, be sure to follow all the instructions here, or you could get a false reading on the dipstick. D D D D When outside temperatures are above 90_F (32_C). At high speed for quite a while. In heavy traffic -- especially in hot weather. 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). Get the vehicle warmed up by driving about 15 miles (24 km) when outside temperatures are above 50_F (10_C). If it's colder than 50_F (10_C), drive the vehicle in in DRIVE (D) until the engine temperature gage moves and then remains steady for 10 minutes. Then follow the hot check procedures. 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 on hot engine parts or exhaust system parts, starting a fire. Be sure to get an accurate reading if you check your transmission fluid. 6-18