Mercury 1999 Mountaineer Owner's Manual page 19

Instrumentation
OIL LIFE RESET TO 100%. (If you have established a personalized oil
reset percentage, the display will show that percentage instead of 100%.)
This reset procedure should be performed only after an oil change to
ensure accurate oil life indications.
Your personalized oil reset percentage allows you to establish a smaller
oil change interval than the manufacturer's recommended interval. To
establish your personalized oil reset percentage:
1. Press and hold the OIL CHANGE RESET control and press the RESET
control while the display is still counting down the 5 seconds to reset.
The display will change to START OIL LIFE AT XXX%.
2. Press the OIL CHANGE RESET control until the displayed percentage
is the personalized oil reset percentage you desire. Your choices are
100%, 90%, 80%, 70%, 60%, 50%, 40% and 30%.
3. Press the RESET control to
complete the procedure. Pressing
any control other than RESET or
FUEL
OIL CHANGE RESET will abort this
procedure and will not establish
your new personalized oil reset
percentage.
When your personalized oil reset
percentage has been established, it
will be used beginning with the
completion of your next OIL CHANGE RESET procedure.
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