From the service manual:
Cooling System Capacity 15.1 Liters (16.0 Quarts)
Cap pressure 89-124 kPa (13-18 psi)
Thermostat Opening Temperature
Starts to Open 90°C (194°F)
Fully Open 99°C (210°F)
I believe that the coolant system capacity is 8.6 quarts ( 8.1 liters ) for your Explorer ( if it has air conditioning )
The two door , 1999 Ford Explorer has a ( 17.3 U.S. gallon gas tank )
The 1999 Ford Explorer owners manual shows ( 20.8 U.S. gallons ) for the 4 door
The repair manual reads...7.8 to 13.2 qts.
( 16.8 gallons ) in the 2003 Ford Explorer Sport
According to the 2013 Ford Explorer Owner Guide : ( 18.6 U.S. gallons )
( 21 ) U.S. gallons on the 2000 Ford Explorer four door
12.5Qts
The 2000 Ford Explorer 4 door is - 21 U.S. gallons ( 79.5 liters )
The gas tank on the 2010 Ford Explorer holds 22.5 gal..
The gas tank on the 2013 Ford Explorer holds 18.6 gal..
The gas tank on the 2004 Ford Explorer holds 22.5 gal..