Fluid Level Check
Remove the automatic transmission dipstick from the tube
Check the transmission fluid level on the dipstick
Automatic transmission dipstick marks; the proper level for a hot transmission is within the shaded area
Check the automatic transmission fluid level at least every 7500 miles (12,000 km). The dipstick can be found in the rear of the engine compartment. The fluid level should be checked only when the transmission is hot (normal operating temperature). The transmission is considered hot after about 15-20 miles (24-32 km) of highway driving.
Although the transmission should be checked while the fluid is at normal operating temperature, do not check it if it is at the extreme high end of the operating temperature range. Wait at least 30 minutes if you have just be driving the vehicle in ambient temperatures in excess of 90°F (32°C), at highway speeds for a long time, in heavy traffic (especially in hot weather) or have been pulling a trailer.
When moving the selector through each range, DO NOT race the engine.
Park the truck on a level surface with the engine idling, then shift the transmission into Park and firmly set the parking brake.
With your foot on the brake pedal, move the selector through each gear range (pausing for about 3 seconds in each gear), then place it in Park. Allow the engine to run at idle about 3 more minutes.
Most of the transmissions for the 4.3L engine are equipped with a flip-top handle on the dipstick. To withdraw these, flip the handle upward, then pull the dipstick from the guide.
With the engine running at a low idle, remove the dipstick, wipe it clean and then reinsert it firmly. Be sure that it has been pushed all the way in, then pause 3 seconds. Remove the dipstick again and check the fluid level while holding it horizontally. The fluid level should be between the upper notch and the FULL HOT line. If the fluid must be checked when it is cool, the level should be between the lower 2 notches.
If the fluid level is low add DEXRON®III automatic transmission fluid. The fluid must be added through the transmission dipstick tube, which is easily accomplished using a funnel. Add fluid gradually, checking the level often as you are filling the transmission. Be extremely careful not to overfill the transmission, as this will cause slippage, seal damage and overheating. Approximately one pint of ATF will raise the fluid level from one notch/line to the other.
Always use DEXRON®III ATF. The use of ATF Type F or any other fluid will cause severe damage to the transmission.
The fluid on the dipstick should always be a bright red color. If it is discolored (brown or black), or smells burnt, serious transmission troubles, probably due to overheating, should be suspected. The transmission should be inspected by a qualified technician to locate the cause of the burnt fluid.