This explains why some of the gauges "jump" from one position to other, instead of slow steady increase:
This is for 98-04 Seville/00-05 Deville (Analog Cluster), 92-97 Sevilles, 92-02 Eldorados similarFactory Service Manual - All Year/All Models said:The engine coolant temperature sensor is located in the engine water jacket and is a resistive type sender. The sensor supplies the engine coolant temperature to the powertrain control module (PCM) via discrete input. The filtered coolant temperature data is sent from the PCM to the IPC, via class 2 serial data messages. The IPC uses the temperature data received from the PCM and a software program to determine the proper coolant temperature to display. When the IPC receives the coolant temperature via class 2 serial data message, it compares the data to a calibratable look up table for the engine configuration. The coolant temperature is transmitted via class 2 serial data message on a change of 1.5°C (2.7°F) or more.
This is for 00-05 Deville (Digital VF Cluster)Factory Service Manual - 2000 Deville / 2000 Seville - Instrument Cluster Gauge Operation said:The IPC determines the proper pointer position on the engine coolant temperature gauge in order to display the relative engine coolant temperature. The engine coolant temperature gauge is labeled C on the left for cold, less than 32°C (90°F) and H on the right for hot, greater than 128°C (262°F). The gauge will be at the center position when the engine coolant is at the nominal temperature, between 88-104°C (190-219°F). The DSPL MODE button on the DIC is used to turn the display ON and OFF. The display will be ON when the speedometer gauge is ON and OFF when the speedometer gauge is OFF.
This is what the FSM tells you about the cooling fan operation:Factory Service Manual - 2000 Deville - Instrument Cluster Gauge Operation said:The IPC has a VF display that shows bars in order to display the relative engine coolant temperature. The engine coolant temperature display is labeled C at the bottom with no bars for cold, less than 40°C (104°F). The engine coolant temperature display is labeled H at the top with 8 bars for hot, greater than 128°C (262°F). The display will be at 4 bars when the engine coolant is at the nominal temperature, between 86-113°C (187-235°F). The DSPL MODE button is used to turn the display ON and OFF.
About Camel Mode/Limp Home ModeFactory Service Manual - All Year/All Models said:PCM will command fan operation when:
Low Speed Fan Operation
Engine coolant temperature exceeds approximately 106°C (223°F).
Transmission fluid temperature exceeds 150°C (302°F).
A/C operation is requested.
After the vehicle is shut OFF if the coolant temperature at key-off is more than 151°C (304°F) and system voltage was more than 12 volts. The fans will stay ON for approximately 3 minutes.
The fans will switch from low to OFF when the coolant drops below 102°C (216°F).
High Speed Fan Operation
Engine coolant temperature reaches 112°C (234°F).
Transmission temperature is more than 151°C (304°F).
When certain DTCs set.
The fans will switch from high to low (except DTCs set) when the coolant drops below 106°C (229°F).
Factory Service Manual - All Year/All Models said:The PCM has the ability to disable 4 injectors during an engine over temperature condition. The engine is considered over temperature whenever the ECT reaches 131°C (268°F). This protection mode permits the PCM to alternate between groups of cylinders, thereby reducing coolant temperature. This is accomplished by disabling the fuel injectors. DTC P1258 is set to show that an overtemperature condition was or is observed by the PCM and that the protection mode has been engaged.
PCM turns ON the SERVICE ENGINE COOLING SYSTEM message.
Engine operates in alternating 4 cylinder mode.
The PCM will illuminate the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.
The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.
A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test.
Use a scan tool to clear DTCs.
Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation.