Runs to cool
10-24-2011, 01:59 AM
#1
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Year: 1995
Model: Cherokee
Engine: 4.0HO
Runs to cool
I know alot of people have problems with overheating, but mine runs really cool, too cool I think. I have read these are suppose to run at 210, but mine doesn't really get above about 1/4 on the gauge, unless it sits and idles for a long time, then it gets close to the 210 mark, but will come right down when I start to drive. I have replaced the t-stat with no effect. It doesn't even have a fan shroud. The summers here get real hot, but it didn't have any effect on it.
Guess I should be happy it doesn't overheat like many do, but if it is designed to run hotter then it might be affecting other things. Whatcha think?
Guess I should be happy it doesn't overheat like many do, but if it is designed to run hotter then it might be affecting other things. Whatcha think?
10-24-2011, 02:43 AM
#2
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Model: Cherokee (XJ)
Engine: 4.0
to cool
I had the overheating issue, I replaced everything and put a 160* t-stat in and now mine runs the same temp your describing. You could go hi-tech and block 1/2 of your radiator with a piece of cardboard...
10-24-2011, 05:47 AM
#3
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There is a good chance that what you are seeing on your dash gauge is inaccurate.
Get a hold of an infrared point and shoot thermometer. They are now widely available and not expensive. Every shop has one of these and they may come out and use it on your engine for free.
Point it directly at the thermostat housing of a hot engine. This will give you a temperature that should be within a few degrees.
Inaccuracy can be caused by the coolant temperature sensor (#1 cause) or even a faulty dash gauge.
You really need an accurate read of what temp the engine is running at.
Get a hold of an infrared point and shoot thermometer. They are now widely available and not expensive. Every shop has one of these and they may come out and use it on your engine for free.
Point it directly at the thermostat housing of a hot engine. This will give you a temperature that should be within a few degrees.
Inaccuracy can be caused by the coolant temperature sensor (#1 cause) or even a faulty dash gauge.
You really need an accurate read of what temp the engine is running at.
10-24-2011, 07:30 AM
#4
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your computer is in open loop until 190 degrees, and therefore doesn't start collection information until then. If you're not getting up to about 200-210, chances are your thermostat is stuck open or you don't have one in there.
10-24-2011, 09:20 AM
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i had this prob once and i figured it out
the temp sensor is located on the driver side top of the radiator and i didnt have enought coolent to make it up to the sensor there for it was only reading the hot air in the radiator. filler up and bam i was reading normal again
the temp sensor is located on the driver side top of the radiator and i didnt have enought coolent to make it up to the sensor there for it was only reading the hot air in the radiator. filler up and bam i was reading normal again
10-24-2011, 09:40 AM
#6
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pretty sure this open loop is a myth, how does coolant temperature control anything? From the research i have done, its the exhaust going to the o2 sensors that controls open and closed loop. i have 160 t-stats in all three of my XJ's and i actually get better gas mileage and they run better. have had zero negative problems. on a hot day in traffic they will still get up to 210 fairly easy. cruising down the highway they sit at 160, a cooler engine will last longer. That is just my opinion, no bashing intended.
10-24-2011, 10:33 AM
#7
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pretty sure this open loop is a myth, how does coolant temperature control anything? From the research i have done, its the exhaust going to the o2 sensors that controls open and closed loop. i have 160 t-stats in all three of my XJ's and i actually get better gas mileage and they run better. have had zero negative problems. on a hot day in traffic they will still get up to 210 fairly easy. cruising down the highway they sit at 160, a cooler engine will last longer. That is just my opinion, no bashing intended.
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10-24-2011, 02:03 PM
#9
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I'd be willing to bet if u plug a scan tool into the ALDL port under the dash, u'll see "closed loop" is entered well before coolant is any where close to so called normal operating temp. Heated O2 sensors reach operating temp within seconds of motor start-up. The loop closes when the O2 sensor(s) starts to function.
10-24-2011, 02:22 PM
#10
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This whole closed or open loop is why I'm posting about it. I still get 20-21 mpg on the hiway. As far as the guage being accurate, I have been meaning to check things out with a laser gun, but it doesn't even seem that hot when I open the hood.
10-24-2011, 02:23 PM
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Engines were engineered to run a certain way. They have tolerances that are designed to be ideal at operating temp for long life. Running an engine cold allows more leakage past the rings to contribute to oil contamination. Another problem with running cold is the inability to boil off water and fuel contaminates from the oil which hurts engine life as well.
I run factory temp thermostats in all engines. A thermostat is not a fix for overheating, it just masks the real problem if it even helps at all.
I run factory temp thermostats in all engines. A thermostat is not a fix for overheating, it just masks the real problem if it even helps at all.
10-24-2011, 02:42 PM
#12
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Have fun... Took an hour to format.
Originally Posted by 95 FSM
OPEN LOOP/CLOSED LOOP MODES OF OPERATION
As input signals to the powertrain control module (PCM) change, the PCM adjusts its response to the output devices. For example, the PCM must calculate different injector pulse width and ignition timing for idle than it does for wide open throttle (WOT). There are several different modes of operation that deter-
mine how the PCM responds to the various input signals.
MODES:
*Open Loop
*Closed Loop
During Open Loop modes, the powertrain control module (PCM) receives input signals and responds only according to preset PCM programming. Input from the oxygen (O2S) sensor is not monitored during Open Loop modes.
During Closed Loop modes, the PCM will monitor the oxygen (O2S) sensor input. This input indicates to the PCM whether or not the calculated injector pulse width results in the ideal air-fuel ratio. This ratio is 14.7 parts air-to-1 part fuel. By monitoring the exhaust oxygen content through the O2S sensor, the PCM can fine tune the injector pulse width. This is done to achieve optimum fuel economy combined with low emission engine performance.
The fuel injection system has the following modes
of operation:
* Ignition switch ON
* Engine start-up (crank)
* Engine warm-up
* Idle
* Cruise
* Acceleration
* Deceleration
* Wide open throttle (WOT)
* Ignition switch OFF
The ignition switch On, engine start-up (crank), engine warm-up, acceleration, deceleration and wide open throttle modes are Open Loop modes. The idle and cruise modes, (with the engine at operating temperature) are Closed Loop modes.
IGNITION SWITCH (KEY-ON) MODE
This is an Open Loop mode. When the fuel system is activated by the ignition switch, the following actions occur:
* The powertrain control module (PCM) pre-positions the idle air control (IAC) motor.
* The PCM determines atmospheric air pressure from the MAP sensor input to determine basic fuel strategy.
* The PCM monitors the engine coolant temperature sensor input. The PCM modifies fuel strategy based on this input.
* Intake manifold air temperature sensor input is monitored
* Throttle position sensor (TPS) is monitored
* The auto shutdown (ASD) relay is energized by the PCM for approximately three seconds.
* The fuel pump is energized through the fuel pump relay by the PCM. The fuel pump will operate for approximately three seconds unless the engine is operating or the starter motor is engaged
* The O2S sensor heater element is energized through the fuel pump relay. The O2S sensor input is not used by the PCM to calibrate air-fuel ratio during this mode of operation.
* The up-shift indicator lamp is illuminated (manual transmission only).
ENGINE START-UP MODE
This is an Open Loop mode. The following actions occur when the starter motor is engaged.
The powertrain control module (PCM) receives inputs from:
* Battery voltage
* Engine coolant temperature sensor
* Crankshaft position sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Starter motor relay
* Camshaft position sensor signal
The PCM monitors the crankshaft position sensor.
If the PCM does not receive a crankshaft position sensor signal within 3 seconds of cranking the engine, it will shut down the fuel injection system.
The fuel pump is activated by the PCM through the fuel pump relay.
Voltage is applied to the fuel injectors with the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
The PCM determines the proper ignition timing according to input received from the crankshaft position sensor.
ENGINE WARM-UP MODE
This is an Open Loop mode. During engine warmup, the powertrain control module (PCM) receives inputs from:
* Battery voltage
* Crankshaft position sensor
* Engine coolant temperature sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Camshaft position sensor signal (in the distributor)
* Park/neutral switch (gear indicator signal—auto. trans. only)
* Air conditioning select signal (if equipped)
* Air conditioning request signal (if equipped)
Based on these inputs the following occurs:
* Voltage is applied to the fuel injectors with the powertrain control module (PCM). The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
* The PCM adjusts engine idle speed through the idle air control (IAC) motor and adjusts ignition timing.
* The PCM operates the A/C compressor clutch through the clutch relay. This is done if A/C has been selected by the vehicle operator and requested by the A/C thermostat.
* If the vehicle has a manual transmission, the upshift lamp is operated by the PCM.
* When engine has reached operating temperature, the PCM will begin monitoring O2S sensor input.
The system will then leave the warm-up mode and go
into closed loop operation.
IDLE MODE
When the engine is at operating temperature, this is a Closed Loop mode. At idle speed, the powertrain control module (PCM) receives inputs from:
* Air conditioning select signal (if equipped)
* Air conditioning request signal (if equipped)
* Battery voltage
* Crankshaft position sensor
* Engine coolant temperature sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Camshaft position sensor signal (in the distributor)
* Battery voltage
* Park/neutral switch (gear indicator signal—auto.trans. only)
* Oxygen sensor
Based on these inputs, the following occurs:
* Voltage is applied to the fuel injectors with the powertrain control module (PCM). The PCM will then control injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
* The PCM monitors the O2S sensor input and adjusts air-fuel ratio by varying injector pulse width. It also adjusts engine idle speed through the idle air control (IAC) motor.
* The PCM adjusts ignition timing by increasing and decreasing spark advance.
* The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been selected by the vehicle operator and requested by the A/C thermostat.
The optional Extended Idle Switch is used to raise the engine idle speed to approximately 1000 rpm.This is when the shifter is in either the Park or Neutral position. A rocker type 2-wire switch (extended idle switch) is mounted to the instrument panel. This switch will supply a ground circuit to the powertrain control module (PCM). The switch is available only with 4.0L engine when supplied with the optional police package.
CRUISE MODE
When the engine is at operating temperature, this is a Closed Loop mode. At cruising speed, the powertrain control module (PCM) receives inputs from:
* Air conditioning select signal (if equipped)
* Air conditioning request signal (if equipped)
* Battery voltage
* Engine coolant temperature sensor
* Crankshaft position sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Camshaft position sensor signal (in the distributor)
* Park/neutral switch (gear indicator signal—auto. trans. only)
* Oxygen (O2S) sensor
Based on these inputs, the following occurs:
* Voltage is applied to the fuel injectors with the PCM. The PCM will then adjust the injector pulse width by turning the ground circuit to each individual injector on and off.
* The PCM monitors the O2S sensor input and adjusts air-fuel ratio. It also adjusts engine idle speed through the idle air control (IAC) motor.
* The PCM adjusts ignition timing by turning the ground path to the coil on and off.
* The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been selected by the vehicle operator and requested by the A/C thermostat.
ACCELERATION MODE
This is an Open Loop mode. The powertrain control module (PCM) recognizes an abrupt increase in throttle position or MAP pressure as a demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width in response to increased throttle opening.
DECELERATION MODE
When the engine is at operating temperature, this is an Open Loop mode. During hard deceleration, the powertrain control module (PCM) receives the following inputs.
* Air conditioning select signal (if equipped)
* Air conditioning request signal (if equipped)
* Battery voltage
* Engine coolant temperature sensor
* Crankshaft position sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Camshaft position sensor signal (in the distributor)
* Park/neutral switch (gear indicator signal—auto. trans. only)
If the vehicle is under hard deceleration with the proper rpm and closed throttle conditions, the PCM will ignore the oxygen sensor input signal. The PCM will enter a fuel cutoff strategy in which it will not supply battery voltage to the injectors. If a hard deceleration does not exist, the PCM will determine the proper injector pulse width and continue injection.
Based on the above inputs, the PCM will adjust engine idle speed through the idle air control (IAC) motor.
The PCM adjusts ignition timing by turning the ground path to the coil on and off.
The PCM opens the ground circuit to the A/C clutch relay to disengage the A/C compressor clutch.
This is done until the vehicle is no longer under deceleration (if the A/C system is operating).
WIDE OPEN THROTTLE MODE
This is an Open Loop mode. During wide open throttle operation, the powertrain control module (PCM) receives the following inputs.
* Battery voltage
* Crankshaft position sensor
* Engine coolant temperature sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Camshaft position sensor signal (in the distributor)
During wide open throttle conditions, the following occurs:
* Voltage is applied to the fuel injectors with the powertrain control module (PCM). The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off. The PCM ignores the oxygen sensor input signal and provides a predetermined amount of additional fuel. This is done by adjusting injector pulse width.
* The PCM adjusts ignition timing by turning the ground path to the coil on and off.
* The PCM opens the ground circuit to the A/C clutch relay to disengage the A/C compressor clutch. This will be done for approximately 15 seconds (if the air conditioning system is operating).
If the vehicle has a manual transmission, the upshift lamp is operated by the PCM.
IGNITION SWITCH OFF MODE
When ignition switch is turned to OFF position, the PCM stops operating the injectors, ignition coil, ASD relay and fuel pump relay.
As input signals to the powertrain control module (PCM) change, the PCM adjusts its response to the output devices. For example, the PCM must calculate different injector pulse width and ignition timing for idle than it does for wide open throttle (WOT). There are several different modes of operation that deter-
mine how the PCM responds to the various input signals.
MODES:
*Open Loop
*Closed Loop
During Open Loop modes, the powertrain control module (PCM) receives input signals and responds only according to preset PCM programming. Input from the oxygen (O2S) sensor is not monitored during Open Loop modes.
During Closed Loop modes, the PCM will monitor the oxygen (O2S) sensor input. This input indicates to the PCM whether or not the calculated injector pulse width results in the ideal air-fuel ratio. This ratio is 14.7 parts air-to-1 part fuel. By monitoring the exhaust oxygen content through the O2S sensor, the PCM can fine tune the injector pulse width. This is done to achieve optimum fuel economy combined with low emission engine performance.
The fuel injection system has the following modes
of operation:
* Ignition switch ON
* Engine start-up (crank)
* Engine warm-up
* Idle
* Cruise
* Acceleration
* Deceleration
* Wide open throttle (WOT)
* Ignition switch OFF
The ignition switch On, engine start-up (crank), engine warm-up, acceleration, deceleration and wide open throttle modes are Open Loop modes. The idle and cruise modes, (with the engine at operating temperature) are Closed Loop modes.
IGNITION SWITCH (KEY-ON) MODE
This is an Open Loop mode. When the fuel system is activated by the ignition switch, the following actions occur:
* The powertrain control module (PCM) pre-positions the idle air control (IAC) motor.
* The PCM determines atmospheric air pressure from the MAP sensor input to determine basic fuel strategy.
* The PCM monitors the engine coolant temperature sensor input. The PCM modifies fuel strategy based on this input.
* Intake manifold air temperature sensor input is monitored
* Throttle position sensor (TPS) is monitored
* The auto shutdown (ASD) relay is energized by the PCM for approximately three seconds.
* The fuel pump is energized through the fuel pump relay by the PCM. The fuel pump will operate for approximately three seconds unless the engine is operating or the starter motor is engaged
* The O2S sensor heater element is energized through the fuel pump relay. The O2S sensor input is not used by the PCM to calibrate air-fuel ratio during this mode of operation.
* The up-shift indicator lamp is illuminated (manual transmission only).
ENGINE START-UP MODE
This is an Open Loop mode. The following actions occur when the starter motor is engaged.
The powertrain control module (PCM) receives inputs from:
* Battery voltage
* Engine coolant temperature sensor
* Crankshaft position sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Starter motor relay
* Camshaft position sensor signal
The PCM monitors the crankshaft position sensor.
If the PCM does not receive a crankshaft position sensor signal within 3 seconds of cranking the engine, it will shut down the fuel injection system.
The fuel pump is activated by the PCM through the fuel pump relay.
Voltage is applied to the fuel injectors with the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
The PCM determines the proper ignition timing according to input received from the crankshaft position sensor.
ENGINE WARM-UP MODE
This is an Open Loop mode. During engine warmup, the powertrain control module (PCM) receives inputs from:
* Battery voltage
* Crankshaft position sensor
* Engine coolant temperature sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Camshaft position sensor signal (in the distributor)
* Park/neutral switch (gear indicator signal—auto. trans. only)
* Air conditioning select signal (if equipped)
* Air conditioning request signal (if equipped)
Based on these inputs the following occurs:
* Voltage is applied to the fuel injectors with the powertrain control module (PCM). The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
* The PCM adjusts engine idle speed through the idle air control (IAC) motor and adjusts ignition timing.
* The PCM operates the A/C compressor clutch through the clutch relay. This is done if A/C has been selected by the vehicle operator and requested by the A/C thermostat.
* If the vehicle has a manual transmission, the upshift lamp is operated by the PCM.
* When engine has reached operating temperature, the PCM will begin monitoring O2S sensor input.
The system will then leave the warm-up mode and go
into closed loop operation.
IDLE MODE
When the engine is at operating temperature, this is a Closed Loop mode. At idle speed, the powertrain control module (PCM) receives inputs from:
* Air conditioning select signal (if equipped)
* Air conditioning request signal (if equipped)
* Battery voltage
* Crankshaft position sensor
* Engine coolant temperature sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Camshaft position sensor signal (in the distributor)
* Battery voltage
* Park/neutral switch (gear indicator signal—auto.trans. only)
* Oxygen sensor
Based on these inputs, the following occurs:
* Voltage is applied to the fuel injectors with the powertrain control module (PCM). The PCM will then control injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
* The PCM monitors the O2S sensor input and adjusts air-fuel ratio by varying injector pulse width. It also adjusts engine idle speed through the idle air control (IAC) motor.
* The PCM adjusts ignition timing by increasing and decreasing spark advance.
* The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been selected by the vehicle operator and requested by the A/C thermostat.
The optional Extended Idle Switch is used to raise the engine idle speed to approximately 1000 rpm.This is when the shifter is in either the Park or Neutral position. A rocker type 2-wire switch (extended idle switch) is mounted to the instrument panel. This switch will supply a ground circuit to the powertrain control module (PCM). The switch is available only with 4.0L engine when supplied with the optional police package.
CRUISE MODE
When the engine is at operating temperature, this is a Closed Loop mode. At cruising speed, the powertrain control module (PCM) receives inputs from:
* Air conditioning select signal (if equipped)
* Air conditioning request signal (if equipped)
* Battery voltage
* Engine coolant temperature sensor
* Crankshaft position sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Camshaft position sensor signal (in the distributor)
* Park/neutral switch (gear indicator signal—auto. trans. only)
* Oxygen (O2S) sensor
Based on these inputs, the following occurs:
* Voltage is applied to the fuel injectors with the PCM. The PCM will then adjust the injector pulse width by turning the ground circuit to each individual injector on and off.
* The PCM monitors the O2S sensor input and adjusts air-fuel ratio. It also adjusts engine idle speed through the idle air control (IAC) motor.
* The PCM adjusts ignition timing by turning the ground path to the coil on and off.
* The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been selected by the vehicle operator and requested by the A/C thermostat.
ACCELERATION MODE
This is an Open Loop mode. The powertrain control module (PCM) recognizes an abrupt increase in throttle position or MAP pressure as a demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width in response to increased throttle opening.
DECELERATION MODE
When the engine is at operating temperature, this is an Open Loop mode. During hard deceleration, the powertrain control module (PCM) receives the following inputs.
* Air conditioning select signal (if equipped)
* Air conditioning request signal (if equipped)
* Battery voltage
* Engine coolant temperature sensor
* Crankshaft position sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Camshaft position sensor signal (in the distributor)
* Park/neutral switch (gear indicator signal—auto. trans. only)
If the vehicle is under hard deceleration with the proper rpm and closed throttle conditions, the PCM will ignore the oxygen sensor input signal. The PCM will enter a fuel cutoff strategy in which it will not supply battery voltage to the injectors. If a hard deceleration does not exist, the PCM will determine the proper injector pulse width and continue injection.
Based on the above inputs, the PCM will adjust engine idle speed through the idle air control (IAC) motor.
The PCM adjusts ignition timing by turning the ground path to the coil on and off.
The PCM opens the ground circuit to the A/C clutch relay to disengage the A/C compressor clutch.
This is done until the vehicle is no longer under deceleration (if the A/C system is operating).
WIDE OPEN THROTTLE MODE
This is an Open Loop mode. During wide open throttle operation, the powertrain control module (PCM) receives the following inputs.
* Battery voltage
* Crankshaft position sensor
* Engine coolant temperature sensor
* Intake manifold air temperature sensor
* Manifold absolute pressure (MAP) sensor
* Throttle position sensor (TPS)
* Camshaft position sensor signal (in the distributor)
During wide open throttle conditions, the following occurs:
* Voltage is applied to the fuel injectors with the powertrain control module (PCM). The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off. The PCM ignores the oxygen sensor input signal and provides a predetermined amount of additional fuel. This is done by adjusting injector pulse width.
* The PCM adjusts ignition timing by turning the ground path to the coil on and off.
* The PCM opens the ground circuit to the A/C clutch relay to disengage the A/C compressor clutch. This will be done for approximately 15 seconds (if the air conditioning system is operating).
If the vehicle has a manual transmission, the upshift lamp is operated by the PCM.
IGNITION SWITCH OFF MODE
When ignition switch is turned to OFF position, the PCM stops operating the injectors, ignition coil, ASD relay and fuel pump relay.
10-24-2011, 03:09 PM
#13
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Year: 1997
Model: Cherokee
Engine: 4.0, comp cam, 99 intake, apn header, neon injectors, Thunderbolt 2.5" High Flow Cat
10-24-2011, 05:03 PM
#15
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Year: 2000.1999,1996
Model: Cherokee
Engine: 4.0
Yup happened to me twice in a row one of those 2 cent t-stat from napa at that maybe a bad batch who knows.If it isn't that it could be the gauge hook up a mech. gauge to know for sure hook it up as close inside the cooling passage as possiable as to many fittings will give you an off reading.
Last edited by 413maxwedge; 10-24-2011 at 05:09 PM.