Never, if you are low on fluid there is a leak - take it in to be inspected. Check your owners manual for proper fluid change schedules.
60.000
Ford recommends changing your transmission fluid every 30,000 miles
Change the fluid and filter every 36,000 miles.
transmission fluid level and what brand should I use in it
The type of automatic transmission fluid to use should be engraved on the transmission fluid dipstick
Mercron transmission fluid is used in a 1978 Ford Thunderbird. Type F fluid can also be used but should not be mixed.
The type of fluid to use should be engraved into the automatic transmission fluid dipstick on a 1998 Ford F-150
The manual transmission on a Ford Ranger should be changed on a regular basis. Fill the transmission with any good quality regular or synthetic transmission fluid.
YOU should use type F transmission fluid in all Ford products prior to 1980.
On a 1991 Ford Explorer : The A4LD automatic transmission uses MERCON automatic transmission fluid according to my Haynes Ford Explorer repair manual * the type of fluid used should be engraved into the automatic transmission fluid level dipstick
The type should be engraved in the automatic transmission fluid dipstick . ( if you have the 5 speed manual transmission it would have Motorcraft MERCON automatic transmission fluid in it from the factory )
It should tell you right on the transmission dipstick.