1997 GMC Suburban Owner's Manual - Page 303

If you do it yourself, be sure to follow all instructions the here, or you could get a false reading on the dipstick. Checking Transmission Fluid Hot 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 (lO"C), drive the vehicle in THIRD (3) until the engine temperaturegage moves and then remains steady for 10 minutes. Then follow the hot check procedures. I 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. Checking Transmission Fluid Cold A cold check is made after the vehicle has been sitting for eighthours or more with the engine off and is used only as a reference. Let engine run at idle for five the minutes if outside temperatures are 50°F ( 10°C) or more. If it's colder than 50°F (1 OOC), you may have to idle the engine longer. Should the fluid level be low during a cold check, you must perform a hot check before adding fluid. This will give you a more accurate reading of the fluid level. Wait at least 30 minutes before checking the transmission fluid level you have been driving: if 0 0 0 0 When outside temperatures areabove 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). 6-21