Ford 2003 Ranger Owner's Manual page 203

Your vehicle was factory-filled with a 50/50 engine coolant and water
concentration. If the concentration of coolant falls below 40% or above
60%, the engine parts could become damaged or not work properly. A
50–50 mixture of coolant and water provides the following:
• Freeze protection down to -36° C (-34° F).
• Boiling protection up to 129° C (265° F).
• Protection against rust and other forms of corrosion.
• Enables calibrated gauges to work properly.
• 2.3L engines
• 3.0L and 4.0L engines
When the engine is cold, check the level of the engine coolant in the
reservoir.
• The engine coolant should be at the "cold fill level" or within the "cold
fill range" as listed on the engine coolant reservoir (depending upon
application).
Maintenance and Specifications
203