1991 Mercury Cougar LS, 3.8 4FACTORY OEM SERVICE PROCEDURE

Cold Engine Lock-Out Function

During cold weather, engine coolant temperature switch controls cold engine lock-out function when ATC system is set for AUTO operation. During lock-out, fan will not operate until engine coolant temperature is above 100Β°F (38Β°C). Switch is located in heater inlet hose.

Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.

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