Automatic Transmission Temperatures
and how manny dings Il get..
JK Jedi
Joined: Feb 2008
Posts: 7,215
Likes: 10
From: Georgia
Ultimately, the two most important places to be concerned with trans fluid temp are the clutch packs and torque converter. These two areas are where almost ALL of the friction in the transmission takes place. The pan is just a reservoir to hold the fluid. Fluid is really not WORKING in the pan.
Thread Starter
JK Jedi Master
Joined: Feb 2008
Posts: 12,907
Likes: 185
From: Maine
Ultimately, the two most important places to be concerned with trans fluid temp are the clutch packs and torque converter. These two areas are where almost ALL of the friction in the transmission takes place. The pan is just a reservoir to hold the fluid. Fluid is really not WORKING in the pan.
The combustion chamber of an engine is a lot hotter than the water in the jacket. However, it is the water temp (and sometimes oil temp) which is universally monitored. (Admittedly a stretch, but sometimes it is good to think in extremes.)
Anyway, the data in the first post is there for whoever is interested. I like knowing my temps are taken from the same area of the transmission all the manufacturer's data is taken. How else would you make a comparison?
Last edited by ronjenx; Jun 9, 2008 at 05:10 PM.
JK Freak
Joined: May 2007
Posts: 571
Likes: 0
From: Marietta, GA
I did a lot of research before I installed my gauge and decided on the inline location to monitor the actual working temp of the fluid. Many people install 2 sending units switched to 1 gauge so t
ey can monitor two points. This may be a good way for you to compare if you wanted to install a second sending unit.
I did mine inline after the cooler, but in previous trucks, I have done them inline before the cooler. After having experience with both, I prefer the "before the cooler" install. A little more fluxuation in the gauge, but no "anxiety" caused by it! I believe this location gives the most accurate representation of the operating temperature of the primary transmission components. I want to know how hot the fluid is getting at the hottest point...logically, that would be before the cooler....not after it and not in the pan.
ey can monitor two points. This may be a good way for you to compare if you wanted to install a second sending unit.
I did mine inline after the cooler, but in previous trucks, I have done them inline before the cooler. After having experience with both, I prefer the "before the cooler" install. A little more fluxuation in the gauge, but no "anxiety" caused by it! I believe this location gives the most accurate representation of the operating temperature of the primary transmission components. I want to know how hot the fluid is getting at the hottest point...logically, that would be before the cooler....not after it and not in the pan.
JK Newbie
Joined: May 2007
Posts: 47
Likes: 0
From: Germany
The highlighted words above are incorrect. The factory sensor projects down into the sump fluid. Here is a quote from the factory service manual:
"The transmission temperature sensor (2) is located in the transmission range sensor (1) and communicates transmission sump temperature to the TCM.
OPERATION
The transmission range sensor (TRS) has an integrated thermistor that the TCM uses to monitor the transmission's sump temperature. Since fluid temperature can affect transmission shift quality and convertor lock up, the TCM requires this information to determine which shift schedule to operate in. The TCM also monitors this temperature data so it can energize the vehicle cooling fan(s) when a transmission “overheat” condition exists. If the thermistor circuit fails, the TCM will revert to calculated oil temperature usage."
Did you read the following, linked in the first post of this thread?
This is what my research has revealed about trans temp probes located in the various points on the 42RLE transmission.
The following is what I have concluded based on my best effort to get the facts.
Line out to the cooler:
This will show temperature of fluid coming out of the trans, but it will be variable with short term spikes as the TC locks and unlocks. Short term temp spikes are normal and not detrimental to transmission fluid life. A probe in this location can lead to unnecessary anxiety.
Line from cooler to transmission:
This will show the fluid after cooling, and will be lower than what the pump picks up from the pan.
In one of the many pressure ports on the side of the transmission:
This will show temp of the fluid only when the particular circuit is in operation. You would have to choose which port to monitor. They are torque converter clutch on, torque converter clutch off, reverse, low/reverse, 2/4, underdrive, overdrive.
This brings us to the pan:
This will show temp of fluid the pump picks up and sends through the transmission. The sump is sort of a "dampener" for fluid temperatures. It reflects the steady state temperature of the fluid. Long term temp rise, which is what degrades the transmission and fluid, will show in the sump. As mentioned above, short spikes in temp as the fluid leaves the transmission are not a factor.
The transmission's factory temp sensor monitors the fluid in the sump. The normal programs in the tranny controller respond to sump fluid temperatures.
The troubleshooting charts and operational limits are based on sump temps.
Some brands of transmission temp gauges recommend an inline probe location IF installing it in the pan is not possible for some reason.
Several local transmission shops recommend the pan location. However, they say most people choose one of the inline locations for ease of installation.
Based on what I have learned, I will be installing the temp sensor in the pan.
"The transmission temperature sensor (2) is located in the transmission range sensor (1) and communicates transmission sump temperature to the TCM.
OPERATION
The transmission range sensor (TRS) has an integrated thermistor that the TCM uses to monitor the transmission's sump temperature. Since fluid temperature can affect transmission shift quality and convertor lock up, the TCM requires this information to determine which shift schedule to operate in. The TCM also monitors this temperature data so it can energize the vehicle cooling fan(s) when a transmission “overheat” condition exists. If the thermistor circuit fails, the TCM will revert to calculated oil temperature usage."
Did you read the following, linked in the first post of this thread?
This is what my research has revealed about trans temp probes located in the various points on the 42RLE transmission.
The following is what I have concluded based on my best effort to get the facts.
Line out to the cooler:
This will show temperature of fluid coming out of the trans, but it will be variable with short term spikes as the TC locks and unlocks. Short term temp spikes are normal and not detrimental to transmission fluid life. A probe in this location can lead to unnecessary anxiety.
Line from cooler to transmission:
This will show the fluid after cooling, and will be lower than what the pump picks up from the pan.
In one of the many pressure ports on the side of the transmission:
This will show temp of the fluid only when the particular circuit is in operation. You would have to choose which port to monitor. They are torque converter clutch on, torque converter clutch off, reverse, low/reverse, 2/4, underdrive, overdrive.
This brings us to the pan:
This will show temp of fluid the pump picks up and sends through the transmission. The sump is sort of a "dampener" for fluid temperatures. It reflects the steady state temperature of the fluid. Long term temp rise, which is what degrades the transmission and fluid, will show in the sump. As mentioned above, short spikes in temp as the fluid leaves the transmission are not a factor.
The transmission's factory temp sensor monitors the fluid in the sump. The normal programs in the tranny controller respond to sump fluid temperatures.
The troubleshooting charts and operational limits are based on sump temps.
Some brands of transmission temp gauges recommend an inline probe location IF installing it in the pan is not possible for some reason.
Several local transmission shops recommend the pan location. However, they say most people choose one of the inline locations for ease of installation.
Based on what I have learned, I will be installing the temp sensor in the pan.
Well done!!! I totally agree to this thoughts ...
JK Jedi
Joined: Feb 2008
Posts: 7,215
Likes: 10
From: Georgia
Can it be said then, the pan is a bad place to put the temp sensor? I figured all the manufacturers put theirs in the pan because it is a good indication of the average temp of the "working" fluid. I could be wrong. Does anyone know a transmission design engineer we could ask?
The combustion chamber of an engine is a lot hotter than the water in the jacket. However, it is the water temp (and sometimes oil temp) which is universally monitored. (Admittedly a stretch, but sometimes it is good to think in extremes.)
Anyway, the data in the first post is there for whoever is interested. I like knowing my temps are taken from the same area of the transmission all the manufacturer's data is taken. How else would you make a comparison?
The combustion chamber of an engine is a lot hotter than the water in the jacket. However, it is the water temp (and sometimes oil temp) which is universally monitored. (Admittedly a stretch, but sometimes it is good to think in extremes.)
Anyway, the data in the first post is there for whoever is interested. I like knowing my temps are taken from the same area of the transmission all the manufacturer's data is taken. How else would you make a comparison?
I don't think I would go that far, because ANY trans fluid temp guage is better than NONE. Although "MY" opinion is that the place to install the trans temp guage is the hottest place that's feasable to install. To me, that's the outlet from the transmission going TO the transmission cooler. We obviously cannot tap a hole into the torque converter, cause it kinda moves. LOL. We cannot get a direct reading off the clutch packs cause taking fluid pressure away from them to read a temp guage would allow for slippage. Not good. I think the best overall place is the outlet going to the cooler. That's where I've always plumbed them in the past on race cars and it's always worked well. I'm not gonna sit here and say "expert" at all, but I've built, raced and torn up automatic transmissions since the late 1970s. I've heard people say stuff like "you know you can run trans fluid TOO cool" I just don't agree. I think the cooler the better.......unless maybe you're in an ultra cold climate or somethin, then it may be different.
Thread Starter
JK Jedi Master
Joined: Feb 2008
Posts: 12,907
Likes: 185
From: Maine
I don't think I would go that far, because ANY trans fluid temp guage is better than NONE. Although "MY" opinion is that the place to install the trans temp guage is the hottest place that's feasable to install. To me, that's the outlet from the transmission going TO the transmission cooler. We obviously cannot tap a hole into the torque converter, cause it kinda moves. LOL. We cannot get a direct reading off the clutch packs cause taking fluid pressure away from them to read a temp guage would allow for slippage. Not good. I think the best overall place is the outlet going to the cooler. That's where I've always plumbed them in the past on race cars and it's always worked well. I'm not gonna sit here and say "expert" at all, but I've built, raced and torn up automatic transmissions since the late 1970s. I've heard people say stuff like "you know you can run trans fluid TOO cool" I just don't agree. I think the cooler the better.......unless maybe you're in an ultra cold climate or somethin, then it may be different.
Last edited by ronjenx; Jun 10, 2008 at 02:10 PM.
JK Jedi
Joined: Feb 2008
Posts: 7,215
Likes: 10
From: Georgia
I can accept others' opinions. Like I said, I offer up my data to those who are interested. I'll continue to update the first post as I see rises in pan temp. One of my aims is to shed some light on the occasional chime I and others have heard as it relates to the fluid temp the computer sees (sump). If temps do climb under some conditions, I want to look at ways to mitigate them under those conditions without installing a supplemental cooler. On my first look under the Jeep, I became suspicious of the close proximity of the exhaust cross-over to the transmission pan. Blocking radiant heat would be good, but I want to see a rise in temp first.
Thread Starter
JK Jedi Master
Joined: Feb 2008
Posts: 12,907
Likes: 185
From: Maine
...and understand, I'm NOT disagreeing with you in the LEAST. I am just saying what has worked for ME for a very long time. No matter what the case, that doesn't necassarily make it right. These transmissions are pretty new beasts. While they are still hydraulic pumps, they are much more complex than a GM turbo 350 or a 727 TorqueFlight. I have not been into a 42RLE......yet. I think the data you have provided is great info. It's a good thread. Folks can see what affect the location of the temp guage has and make up their own minds. Talking about the "chime".....do happen to know where the sensor is that makes the chime sound? That might be an interesting place for the temp guage.
JK Jedi
Joined: Feb 2008
Posts: 7,215
Likes: 10
From: Georgia
The factory sensor is on the left side of the transmission, projecting vertically down into the sump. When I had the pan off, I did not notice if it was visible as my sliding in and out from under the vehicle was always from the right side. The fluid level is well above the pan parting line, and that is the shallow side of the pan. If you have one of these apart sometime, I would be interested in what you see and learn.