Mercury 1999 Mountaineer Owner's Manual page 202

Maintenance and care
4.0L SOHC V6 engine
5.0L V8 engine
1. Start the engine and let it run until it reaches normal operating
temperature (the engine coolant temperature gauge indicator will be
near the center of the normal area between H and C).
2. While the engine idles, turn the steering wheel left and right several
times.
3. Turn the engine off.
4. Check the fluid level in the reservoir.
5. The fluid level should be between the MIN and MAX lines. Do not add
fluid if the level is in this range.
7. If the fluid is low, add fluid in small amounts, continuously checking
the level until it reaches the correct operating range. Be sure to put the
cap back on the reservoir.
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