what does the normal engine oil temp have to be before it will run normally
167° F.
That's the short answer. Here's the full Nelson:
The cold ambient pkg includes high-idle and exhaust back pressure valve operation. They are controlled by the engine computer (PCM) based on both intake air temp (IAT) and engine oil temp (EOT).
Per the Ford diagnostic manual:
Exhaust Back-Pressure Sensor
The Exhaust Back-Pressure sensor is a variable capacitor sensor that is supplied a 5-volt reference signal by the PCM and returns a linear analog voltage signal that indicates pressure. The Exhaust Back-Pressure sensor measures the pressure in the RH exhaust manifold. This sensor is used in conjunction with the exhaust back-pressure regulator to form a closed loop exhaust back-pressure control system.
The exhaust back-pressure is controlled by the PCM to provide more heat to the coolant for cab heating when ambient air temperature is below 7°C (45°F) and engine oil temperature is below 75°C (167°F) during low load, low speed operating conditions.
An open or short in the Exhaust Back-Pressure sensor wiring will result in a low out of range voltage at the PCM, and the PCM will disable Exhaust Back-Pressure control.
Engine Oil Temperature Sensor
The Engine Oil Temperature sensor is a thermistor mounted to the oil reservoir whose resistance decreases as engine oil temperature increases. The Engine Oil Temperature signal is used by the PCM to calculate fuel quantity, injection timing, glow plug operation and exhaust back-pressure.
At low ambient air temperatures, and oil temperature below 50°C (122°F), low idle is increased to a maximum of 1300 rpm to increase engine warm-up. Fuel quantity and timing is controlled throughout the total operating range to provide adequate torque and power.
An Engine Oil Temperature signal detected out of range, high or low, by the PCM will cause the PCM to assume an engine oil temperature of 20°C (68°F) for starting purposes and 100°C (212°F) for operating purposes. The Malfunction Indicator Lamp in the instrument cluster will be illuminated as long as the fault condition exists.
Intake Air Temperature Sensor
The Intake Air Temperature (IAT) Sensors are thermistor devices in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The IAT signal provides air temperature information to the PCM. The PCM uses the air temperature information to operate the Exhaust Back-Pressure (EBP) system and to determine the cold idle setpoint. During long idle periods at cold ambient temperatures, the setpoint will increase engine rpm.
