Ford F-650 2001 Owner's Manual page 170

Maintenance and care
Transmission fluid level should be checked by your dealer or a qualified
service technician.
If you must add transmission fluid, make sure the correct type of fluid is
being used. The type of fluid used is indicated in your Allison Automatic
Transmission Operator's Manual.
Use of a non-approved automatic transmission fluid may cause
internal transmission component damage.
Manual transmission fluid
Refer to your scheduled maintenance guide for transmission fluid level
checks and fluid change intervals.
Your manual transmission may be filled with an optional synthetic fluid
which allows the use of extended service intervals. A tag on the filler
plug will identify the use of the synthetic fluid.
Use only fluid that meets Ford specifications (refer to Lubricant
specifications in the Capacities and specification chapter).
Use of a non-approved transmission fluid may cause internal
transmission component damage.
For location of the transmission filler plug, refer to your transmission
operator's manual or Transmission Refill Capacities in the Capacities
and specifications chapter.
Check your transmission fluid level using the following procedure:
1. Park the vehicle on level ground.
2. Set the parking brake and shift into 1 (First) and turn the engine off.
3. Clean any dirt from around the filler plug.
4. Remove the filler plug and inspect the fluid level.
5. The fluid level should be up to the bottom of the filler plug opening.
6. If necessary, add enough fluid through the filler plug opening so that
the fluid level is at the bottom of the opening.
7. Clean and install the filler plug securely.
Drain and refill your transmission fluid using the following procedure:
1. Drain the transmission while the fluid is warm.
2. Park the vehicle on level ground.
3. Set the parking brake and shift into 1 (First) and turn the engine off.
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