Ford Mustang Owner's Manual page 226

Coolant refill capacity
To find out how much fluid your vehicle's
cooling system can hold, refer to Refill Capacities
in the Capacities and Specifications chapter.
Have your dealer check the engine cooling
system for leaks if you have to add more than a
quart (liter) of engine coolant per month.
Severe winter climate
If you drive in extremely cold climates (less than
-34˚F [-36˚C]), it may be necessary to increase
the coolant concentration above 50%. Refer to
the chart on the coolant container to ensure the
coolant concentration in your vehicle is such that
the coolant will not freeze at the temperature
level in which you drive during winter months.
Never increase the engine coolant concentration
above 60%. Leave a 50/50 mixture of engine
coolant and water in your vehicle year-round in
non-extreme climates.
Engine Coolant Drain and Flush
Proper procedures for a complete coolant drain
and flush of the cooling system can be found in
the Car Service Manual. Following these
recommended procedures will ensure that the
specified coolant level and a 50/50 or
appropriate mixture of coolant and water is
maintained.
Engine Coolant Refill Procedure
When the entire cooling system is drained and
refilled, the following procedure should be used
to ensure a complete fill:
NOTE: It is imperative the following
procedure be adhered to. Failure to do
so could result in damage to your
engine.
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