Engine Coolant Temperature Gauges / Cooling Fans Operation Explained
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  • 2 Post By Submariner409
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Northstar Engines and System Technical Discussion Discussion, Engine Coolant Temperature Gauges / Cooling Fans Operation Explained in Cadillac Engine Technical Discussion; ...
  1. #1
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    Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    This explains why some of the gauges "jump" from one position to other, instead of slow steady increase:
    Quote Originally Posted by Factory Service Manual - All Year/All Models
    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 1.5C (2.7F) or more.
    This is for 98-04 Seville/00-05 Deville (Analog Cluster), 92-97 Sevilles, 92-02 Eldorados similar
    Quote Originally Posted by Factory Service Manual - 2000 Deville / 2000 Seville - Instrument Cluster Gauge Operation
    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 32C (90F) and H on the right for hot, greater than 128C (262F). The gauge will be at the center position when the engine coolant is at the nominal temperature, between 88-104C (190-219F). 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 for 00-05 Deville (Digital VF Cluster)
    Quote Originally Posted by Factory Service Manual - 2000 Deville - Instrument Cluster Gauge Operation
    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 40C (104F). The engine coolant temperature display is labeled H at the top with 8 bars for hot, greater than 128C (262F). The display will be at 4 bars when the engine coolant is at the nominal temperature, between 86-113C (187-235F). The DSPL MODE button is used to turn the display ON and OFF.
    This is what the FSM tells you about the cooling fan operation:
    Quote Originally Posted by Factory Service Manual - All Year/All Models
    PCM will command fan operation when:

    Low Speed Fan Operation
    Engine coolant temperature exceeds approximately 106C (223F).
    Transmission fluid temperature exceeds 150C (302F).
    A/C operation is requested.
    After the vehicle is shut OFF if the coolant temperature at key-off is more than 151C (304F) 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 102C (216F).

    High Speed Fan Operation
    Engine coolant temperature reaches 112C (234F).
    Transmission temperature is more than 151C (304F).
    When certain DTCs set.
    The fans will switch from high to low (except DTCs set) when the coolant drops below 106C (229F).
    About Camel Mode/Limp Home Mode
    Quote Originally Posted by Factory Service Manual - All Year/All Models
    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 131C (268F). 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.
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    Good post - damn good post.

    Now you see why my temp gauge picture (posted everywhere) says "Your results may vary". Jake posted, a year ago, that the gauges were highly damped at the 12:00 position............see the sticky post just below this one........

    For your car the only way to get the real gauge picture is to use a real time logging function on the OBD port - that will give you YOUR temperature readings in YOUR car.
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    This also explains why we don't see any 00-05 Deville (digital dash) members talking about temp gauge fluctuations. That gauge is even more damped than the analog one for Seville/DTS(or some DHS with options).
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    Based on this sticky and some further work with temp guns and cardboard, the revised temp gauge for the late 90's - 2004 FWD series of cars is in my albums. Click my username, open the profile. Left column, 2 albums, 6 pages of Northstar stuff. it's also later in this thread - Post #14.

    Celsius to Farenheit converter: www.wbuf.noaa.gov/tempfc.htm
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    This is very normal, nothing to worry about - about 215 degrees:

    (The dash temp readout is ambient (outside) temperature........)




    But, you should start worrying about it when you see something like this:






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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    Something that i just never have been able to get over is
    when i drive around ac on and its 95 of or high outside and im in heavy traffic i have seen my guage go to where it is in the second picture here
    ones i get moving it start to back down
    i get really nervous when that happens i know im used to it running around 225-230 every now and then but still worry about it
    i know that 215-220 is normal to see even 220-225 at times
    but it has gotten up to 240 on me and nothing is wrong i do a block test it all comes back good no smoke no loosing coolant no burning smell or anything
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    You'd be better off starting a thread. Before that, search for "Northstar overheating" and "Northstar head gaskets" to gather some info about cooling system diagnosis.

    EDIT #1: Oops, you already have a thread on Seville/Eldorado forum. Please post symptoms in your thread to organize it.
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    For reference to gauges and cooling system parts, click on my username, open my profile. Two picture albums in there with many cooling system pictures and diagrams.
    maeng9981 and maeng9981 like this.
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    How do you get the current temp to show in the display (as shown in Thumperpup's picture)?
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    Quote Originally Posted by Kiwi-nadian View Post
    How do you get the current temp to show in the display (as shown in Thumperpup's picture)?
    No way for a 98-04 unless you get a secondary scanner system like ScanGauge. Those are ambient temperature readings.

    If you are talking about the ambient temperature reading, you can scroll through DIC using INFO up and down button.
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    So, based on this post, I could assume that if the cooling fans aren't coming on when the AC is engaged or when the engine is over heating, but will come on when I disconnect the ECT sensor, then I have a PCM fault?
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    Not necessarily. There are fuses, relays, ECT senor, the fan motors to be considered.
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    Northstar thermostats are designed to start opening at 188 and it fully opens at 206. Running temperature anywhere between 188-224 is normal and it's designed to run within that temperature range. Northstar thermostats are very reliable (honestly I never heard of the problem actually being thermostats). If you are letting your car idle, it should reach up until 222-224 and switch the fan on. That's the normal operation.
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    Updated this last November ..................... any Northstar temp gauge with 9 tick marks total will have the same temperature readings per mark.
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    Re: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained

    Quote Originally Posted by maeng9981 View Post
    Northstar thermostats are designed to start opening at 188 and it fully opens at 206. Running temperature anywhere between 188-224 is normal and it's designed to run within that temperature range. Northstar thermostats are very reliable (honestly I never heard of the problem actually being thermostats). If you are letting your car idle, it should reach up until 222-224 and switch the fan on. That's the normal operation.
    222-224 Fans ON LOW. temp drops to 211-213 Fans OFF. Temp back up to 222-224 and the cycle begins anew.
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