: Engine Coolant Temperature Gauges / Cooling Fans Operation Explained



maeng9981
06-07-11, 05:21 AM
This explains why some of the gauges "jump" from one position to other, instead of slow steady increase:

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


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)


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:


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


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.

Submariner409
06-07-11, 11:18 AM
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.

maeng9981
06-07-11, 11:23 PM
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).

Submariner409
06-11-11, 05:46 PM
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 (http://www.wbuf.noaa.gov/tempfc.htm)

maeng9981
09-30-11, 04:20 AM
This is very normal, nothing to worry about - about 215 degrees:

(The dash temp readout is ambient (outside) temperature........)
http://i.imgur.com/VJwEn.jpg



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




http://img33.imageshack.us/img33/4729/01071818.jpg

http://img155.imageshack.us/img155/697/01071905.jpg

ThumperPup
10-02-11, 10:07 PM
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

maeng9981
10-06-11, 03:21 AM
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.

Submariner409
11-23-11, 10:44 AM
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.

Kiwi-nadian
12-01-11, 02:53 AM
How do you get the current temp to show in the display (as shown in Thumperpup's picture)?

maeng9981
12-01-11, 04:10 AM
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.

Kiwi-nadian
12-01-11, 03:01 PM
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?

Ranger
12-01-11, 03:43 PM
Not necessarily. There are fuses, relays, ECT senor, the fan motors to be considered.

maeng9981
12-10-11, 06:20 AM
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.

Submariner409
02-16-13, 12:22 PM
Updated this last November ..................... any Northstar temp gauge with 9 tick marks total will have the same temperature readings per mark.

CadillacLuke24
02-16-13, 12:45 PM
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.