Which Thermostat???
CF Veteran
Joined: Jun 2010
Posts: 2,117
Likes: 3
From: Ohio
Year: 1998
Model: Cherokee
Engine: 4.0 stock
You are saying that as a universal thing for all vehicles of all years? Who is spreading myths now?
There are so many variables that makes the ECU enter closed loop mode coolant temp is just one. I don't have software for my Jeep but I know my Camaro goes into closed loop mode when the coolant temp reaches 170'F within 5 minutes. If not I get a code P0125. BTW both have heated O2 sensors so that makes no difference.
There are so many variables that makes the ECU enter closed loop mode coolant temp is just one. I don't have software for my Jeep but I know my Camaro goes into closed loop mode when the coolant temp reaches 170'F within 5 minutes. If not I get a code P0125. BTW both have heated O2 sensors so that makes no difference.
Member
Joined: May 2010
Posts: 193
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Model: Cherokee
Banned
Joined: Oct 2009
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Hey guys. I'm replacing the thermostat in my 96 Cherokee as part of a water pump replacement. I know the 195* t-stat is stock, but I've heard guys say that a 180* t-stat actually helps in hotter climates. I'm in Tampa, FL, and it's freakin hot. I don't really even understand the differences in the temp ratings on t-stats... why would a 180* serve me better than a stock 195*? Can someone educate a novice please? Thanks!
While all these cats are arguing over what stats work and which don't. Some over look simple crap like air filter and clean fluids and making sure there are no debris in the air box. Assuming your just trying to maintain "normal" temps.
CF Veteran
Joined: Nov 2009
Posts: 8,172
Likes: 17
From: The Republic of TEXAS
Year: 1998
Model: Cherokee
Engine: 4.0L HO
I believe the t-stat allows the coolant to flow to the radiator, when it opens. Coolant will flow to the heater core the moment the engine is started, presuming of course the heater controls on the dash are set to heat. Your just kidding with me, right?
CF Veteran
Joined: Nov 2009
Posts: 8,172
Likes: 17
From: The Republic of TEXAS
Year: 1998
Model: Cherokee
Engine: 4.0L HO
You are saying that as a universal thing for all vehicles of all years? Who is spreading myths now?
There are so many variables that makes the ECU enter closed loop mode coolant temp is just one. I don't have software for my Jeep but I know my Camaro goes into closed loop mode when the coolant temp reaches 170'F within 5 minutes. If not I get a code P0125. BTW both have heated O2 sensors so that makes no difference.
There are so many variables that makes the ECU enter closed loop mode coolant temp is just one. I don't have software for my Jeep but I know my Camaro goes into closed loop mode when the coolant temp reaches 170'F within 5 minutes. If not I get a code P0125. BTW both have heated O2 sensors so that makes no difference.
The ScanGauge on our XJ as well as our Saturn, Toyota and Pontiac show all of them to enter closed loop within seconds of engine start-up. That means they're running clean and lean, almost from the get-go.
Why would it be necessary for coolant to reach a certain temp in order for the engine to run clean and lean?
CF Veteran
Joined: Jun 2010
Posts: 2,117
Likes: 3
From: Ohio
Year: 1998
Model: Cherokee
Engine: 4.0 stock
You have plugged a scan tool into your Camaro's ALDL port and watched the system go from open loop to closed loop and the system waits until coolant temp reaches 170F before entering closed loop??????? So it's polluting the air 4 1/2 minutes longer than most other vehicles with heated O2 sensor(s).
The ScanGauge on our XJ as well as our Saturn, Toyota and Pontiac show all of them to enter closed loop within seconds of engine start-up. That means they're running clean and lean, almost from the get-go.
Why would it be necessary for coolant to reach a certain temp in order for the engine to run clean and lean?
The ScanGauge on our XJ as well as our Saturn, Toyota and Pontiac show all of them to enter closed loop within seconds of engine start-up. That means they're running clean and lean, almost from the get-go.
Why would it be necessary for coolant to reach a certain temp in order for the engine to run clean and lean?
wait... your kidding right? I hooked no such "scan tool" to my Camaro's OBD port. I hooked up a laptop using an interface cable.
I didn't "pollute" as I used this new thing they call "charts". I can do what they call "logging" which means that I can show many different readings on a graph as well as a table for time vs whatever I want while driving around.
This means other drivers and pedestrians are safer around me then you because I don't have to look at readings on a tiny LCD screen while swerving to avoid the mom with kids crossing the street. With my tuning setup I can do a lot more then the dinky scan tools displaying questionable data.
Oh and my Camaro has 2 heated O2 sensors. 1 on each bank and 1 downdraft O2 sensor
Last edited by razor02097; Jul 1, 2010 at 06:30 PM.
CF Veteran
Joined: Nov 2009
Posts: 8,172
Likes: 17
From: The Republic of TEXAS
Year: 1998
Model: Cherokee
Engine: 4.0L HO
I guess that makes you 'da man.....one hand on the wheel, one hand on a keyboard and one or both eyes on a 17" monitor going from one non-street legal fuel map to another.
CF Veteran
Joined: Jun 2010
Posts: 2,117
Likes: 3
From: Ohio
Year: 1998
Model: Cherokee
Engine: 4.0 stock
You have absolutely no idea what you are talking about. your ignorance really shows.
Last edited by razor02097; Jul 1, 2010 at 08:42 PM.
Junior Member
Joined: Dec 2009
Posts: 69
Likes: 0
From: South Florida, USA
Year: 1995
Model: Cherokee
Engine: 4.0
My guess is that the XJ PCM doesn't actually send anything saying it switched from open to closed loop and the ScanGauge is guessing (incorrectly) based on some other parameter. Should be an easy test, disconnect your CTS and see if the ScanGauge display reverts from closed to open loop.
-E
CF Veteran
Joined: May 2009
Posts: 10,423
Likes: 61
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
The "myth" is perpetuated by the FSM in section 14-30. It says both that the O2 sensor is not monitored during warm-up and that engine temperature triggers the switch to closed loop.
My guess is that the XJ PCM doesn't actually send anything saying it switched from open to closed loop and the ScanGauge is guessing (incorrectly) based on some other parameter. Should be an easy test, disconnect your CTS and see if the ScanGauge display reverts from closed to open loop.
-E
My guess is that the XJ PCM doesn't actually send anything saying it switched from open to closed loop and the ScanGauge is guessing (incorrectly) based on some other parameter. Should be an easy test, disconnect your CTS and see if the ScanGauge display reverts from closed to open loop.
-E
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 determine
how the PCM responds to the various input signals.
MODES
² Open Loop
² 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:
² Ignition switch ON
² Engine start-up (crank)
² Engine warm-up
² Idle
² Cruise
² Acceleration
² Deceleration
² Wide open throttle (WOT)
² 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
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 determine
how the PCM responds to the various input signals.
MODES
² Open Loop
² 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:
² Ignition switch ON
² Engine start-up (crank)
² Engine warm-up
² Idle
² Cruise
² Acceleration
² Deceleration
² Wide open throttle (WOT)
² 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
Member
Joined: May 2010
Posts: 193
Likes: 1
Model: Cherokee
I have data logged several cars of mine and the whole point of doing this is so the info the car is reading while driving is saved for AFTER the drive so you don't have to look at it while driving...
Thread Starter
Junior Member
Joined: Jun 2010
Posts: 51
Likes: 1
From: Rockingham County, VA
Year: 1996
Model: Cherokee
Engine: 4.0 I6
Don't let her lie to you.
I've recently solved this overheating problem. Figured it would be a good idea to post some follow-up on this overheating problem I've been having... I know this is one of the mantras of this forum. Hopefully this helps someone.
So I had my water pump crap out back in June, and the repair journey went like this:
Few days ago, I took it into my mechanic, and he tells me that after driving it and putting an infared gun on it, the temp gauge is lying. It's actually running cool. Looking for the right temp sender now.
Anyway, I guess the moral here is that when she tells you she's running hot, don't take the gauge as the final authority.
Hope this helps those like-minded with me who want to still see XJ's on the road 20 years from now.
So I had my water pump crap out back in June, and the repair journey went like this:
- Replaced water pump, t-stat & housing, temp sensor, cleaned hoses, gave it new coolant, burped - still overheating (almost in red, according to dash gauge)
- Replaced temp sender unit (in the back of the block), cause I thought maybe I was getting a false reading, and new gauge still says overheating.
- Replaced radiator w/ 2-row all aluminum (still overheating, though not as bad).
Few days ago, I took it into my mechanic, and he tells me that after driving it and putting an infared gun on it, the temp gauge is lying. It's actually running cool. Looking for the right temp sender now.
Anyway, I guess the moral here is that when she tells you she's running hot, don't take the gauge as the final authority.
Hope this helps those like-minded with me who want to still see XJ's on the road 20 years from now.
Newbie
Joined: Nov 2010
Posts: 14
Likes: 0
From: Colorado
Year: 1997
Model: Cherokee
Engine: 4.0L
You guys might find this link interesting in regards to coolant temp and PCM.
http://www.aa1car.com/library/coolant_sensors.htm
http://www.aa1car.com/library/coolant_sensors.htm
Senior Member
Joined: May 2010
Posts: 889
Likes: 2
From: Detroit, MI
Year: 1994
Model: Cherokee
Engine: 4.0
You guys might find this link interesting in regards to coolant temp and PCM.
http://www.aa1car.com/library/coolant_sensors.htm
http://www.aa1car.com/library/coolant_sensors.htm
That was excellent. A "must read" before changing your thermostat...
Newbie
Joined: Nov 2010
Posts: 14
Likes: 0
From: Colorado
Year: 1997
Model: Cherokee
Engine: 4.0L
Ok. It appears I have solved my No Heat in the cabin problem. I hooked a scanner up to the car and drove it around. The coolant temp never got above 167 degrees. That was after I went through the whole radiator burping process.
So I bought a failsafe 195 degree thermostat and replaced it. I went through the whole burping process again. Which I can't believe is such a process on these xj's. The spill-free funnel system would be a big plus. But I couldn't find one and they are like $30. I had a piece of radiator hose that fit snuggly into the radiator opening so I kept it filled up with coolant. Ran the engine, sqeezed the radiator hose, brought the RPM's up, Blah, Blah, Blah.
The heat blowing out will not cook a hot dog, but it diffinity has heat now where there was none.
So I bought a failsafe 195 degree thermostat and replaced it. I went through the whole burping process again. Which I can't believe is such a process on these xj's. The spill-free funnel system would be a big plus. But I couldn't find one and they are like $30. I had a piece of radiator hose that fit snuggly into the radiator opening so I kept it filled up with coolant. Ran the engine, sqeezed the radiator hose, brought the RPM's up, Blah, Blah, Blah.
The heat blowing out will not cook a hot dog, but it diffinity has heat now where there was none.