2009 Hummer H3T Owner's Manual - Page 254

5-18 Service and Appearance Care 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. Too little fluid could cause the transmission to overheat. Be sure to get an accurate reading if you check your transmission fluid. Wait at least 30 minutes before checking the transmission fluid level if you have been driving: Get the vehicle warmed up by driving about 15 miles (24 km) when outside temperatures are above 50°F (10°C). If it is colder than 50°F (10°C), drive the vehicle in 3 (Third) until the engine temperature gage moves and then remains steady for 10 minutes. A cold fluid check can be made after the vehicle has been sitting for eight hours or more with the engine off, but this is used only as a reference. Let the engine run at idle for five minutes if outside temperatures are 50°F (10°C) or more. If it is colder than 50°F (10°C), the engine might have to idle longer. Should the fluid level be low during this cold check, check the fluid hot before adding fluid. Checking the fluid hot gives a more accurate reading of the fluid level. Automatic Transmission Fluid When to Check and Change Automatic Transmission Fluid A good time to check the automatic transmission fluid level is when the engine oil is changed. Change the fluid and filter at the intervals listed in Additional Required Services on page 6-6, and be sure to use the transmission fluid listed in Recommended Fluids and Lubricants on page 6-12. • When outside temperatures are above 90°F (32°C). How to Check Automatic Transmission Fluid Because this operation can be a little difficult, you may choose to have this done at the dealer/retailer service department. If adding it yourself, be sure to follow all the instructions here, or there could be a false reading on the dipstick. • 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).