Ford Mercury Villager 1997 Owner's Manual page 294

Power steering fluid reservoir
5. If the power steering fluid is low, add fluid in small
amounts, continuously checking the level, until the fluid is
between the minimum (MIN) and maximum (MAX) lines on the
reservoir. Do not overfill. To find out how much fluid your
vehicle's reservoir for the power steering fluid will hold, see
Refill Capacities, Motorcraft Parts, and Lubricant Specifications
in the Capacities and Specifications chapter.
Use only power steering fluid that meets Ford Specification such
as MERCON ATF XT-2-QDX (or equivalent).
NOTE: If the power steering fluid is low, do not drive your
vehicle for a long period of time before adding fluid.
This can damage the power steering pump.
If you must check the power steering fluid when it is cold, make
sure that the fluid reaches at least the minimum (MIN) mark.
The reading will only be accurate if the fluid temperature is
approximately 70° to 100° F (21° to 38° C).
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