Tranny Temp

jeremesh · **Posted:** Mon Sep 15, 2008 5:13 pm

So while I was driving on the beach the other day, I had to stop twice because my trans temp light came on. What should I do to make sure this doesn't become a common occurrence? Also, is there a fairly cheap and easy to install trans temp gauge out there that I could put in?

tjkj2002 · **Posted:** Mon Sep 15, 2008 6:27 pm

jeremesh wrote:

So while I was driving on the beach the other day, I had to stop twice because my trans temp light came on. What should I do to make sure this doesn't become a common occurrence? Also, is there a fairly cheap and easy to install trans temp gauge out there that I could put in?

Use 4low and install a '02 KJ radiator with the in-radiator trans cooler then add a massive AUX cooler.

jason thompson · **Posted:** Mon Sep 15, 2008 7:14 pm

jeremesh wrote:

So while I was driving on the beach the other day, I had to stop twice because my trans temp light came on. What should I do to make sure this doesn't become a common occurrence? Also, is there a fairly cheap and easy to install trans temp gauge out there that I could put in?

as it was said run in 4 low
put the tranny in first not drive
install an aux tranny cooler

The one I have in my TJ ,trail beater, came from 4wd Hardware
it is a flex a lite 4 pass generic cooler ,$30, and it comes with every thing you need
They have an up grade that has a small fan on it but it is way over kill ,unless you live where it gets up to 110 or more and you are wheeling for hours in that heat
Just put it right out in front of the condenser coils and let the engine fan pull the air across it

jeremesh · **Posted:** Mon Sep 15, 2008 7:36 pm

tjkj2002 wrote:

jeremesh wrote:

So while I was driving on the beach the other day, I had to stop twice because my trans temp light came on. What should I do to make sure this doesn't become a common occurrence? Also, is there a fairly cheap and easy to install trans temp gauge out there that I could put in?

Use 4low and install a '02 KJ radiator with the in-radiator trans cooler then add a massive AUX cooler.

But should I make a 26 mile beach run in 4 low?

tjkj2002 · **Posted:** Mon Sep 15, 2008 7:38 pm

jeremesh wrote:

tjkj2002 wrote:

jeremesh wrote:

So while I was driving on the beach the other day, I had to stop twice because my trans temp light came on. What should I do to make sure this doesn't become a common occurrence? Also, is there a fairly cheap and easy to install trans temp gauge out there that I could put in?

Use 4low and install a '02 KJ radiator with the in-radiator trans cooler then add a massive AUX cooler.

But should I make a 26 mile beach run in 4 low?

If your overheating the tranny in 2hi or 4hi,then yes run it in 4low at 10-15mph,just leave the tranny in O/D.

Jeepjeepster · **Posted:** Mon Sep 15, 2008 8:13 pm

Did you have it limited to a lower gear?

If you dont have the Towing package with the engine driven fan you need to keep the electric fan on at low speeds to pull air through the tranny cooler. ontop of that, listen to what has been said above and get a bigger tranny cooler.

My engine and tranny run cooler if I use the A/C. Wonderful setup. :roll:

jason thompson · **Posted:** Mon Sep 15, 2008 8:34 pm

tjkj2002 wrote:

jeremesh wrote:

tjkj2002 wrote:

jeremesh wrote:

So while I was driving on the beach the other day, I had to stop twice because my trans temp light came on. What should I do to make sure this doesn't become a common occurrence? Also, is there a fairly cheap and easy to install trans temp gauge out there that I could put in?

Use 4low and install a '02 KJ radiator with the in-radiator trans cooler then add a massive AUX cooler.

But should I make a 26 mile beach run in 4 low?

If your overheating the tranny in 2hi or 4hi,then yes run it in 4low at 10-15mph,just leave the tranny in O/D.

I would not leave it in O/D
I would at most run it in Drive with the O/D locked out but I would watch it closely for gear hunting ,lots of shifting
if it is then drop it to 2nd and let the engine run at 3000 rpms if needed ,I do it all the time so I know it will not hurt
I ran for close to 700 miles turning 3000 rpm ,now granted it was on the highway and in 2wd but the rpm did not hurt any thing

jeremesh · **Posted:** Mon Sep 15, 2008 9:19 pm

Jeepjeepster wrote:

Did you have it limited to a lower gear?

If you dont have the Towing package with the engine driven fan you need to keep the electric fan on at low speeds to pull air through the tranny cooler. ontop of that, listen to what has been said above and get a bigger tranny cooler.

My engine and tranny run cooler if I use the A/C. Wonderful setup. :roll:

I was in drive the whole time. first 26 miles I was in 4 hi most of the time. Second 26 miles I was in 2wd most of time. Light came on about the same point both times.

jason thompson · **Posted:** Mon Sep 15, 2008 9:26 pm

jeremesh wrote:

Jeepjeepster wrote:

Did you have it limited to a lower gear?

If you dont have the Towing package with the engine driven fan you need to keep the electric fan on at low speeds to pull air through the tranny cooler. ontop of that, listen to what has been said above and get a bigger tranny cooler.

My engine and tranny run cooler if I use the A/C. Wonderful setup. :roll:

I was in drive the whole time. first 26 miles I was in 4 hi most of the time. Second 26 miles I was in 2wd most of time. Light came on about the same point both times.

shifting gears and tranny slipage makes heat
heat makes the temp light come one
stop the gear shifting and the tranny will not get hot

lower gears make it so that the engine does not need to work as hard but they will not keep the tranny from shifting
you need to put it in the lowest gear you can and keep the rpm higher than you think you need
this will help every thing to work less

jeremesh · **Posted:** Mon Sep 15, 2008 9:45 pm

jason thompson wrote:

tjkj2002 wrote:

jeremesh wrote:

tjkj2002 wrote:

jeremesh wrote:

So while I was driving on the beach the other day, I had to stop twice because my trans temp light came on. What should I do to make sure this doesn't become a common occurrence? Also, is there a fairly cheap and easy to install trans temp gauge out there that I could put in?

Use 4low and install a '02 KJ radiator with the in-radiator trans cooler then add a massive AUX cooler.

But should I make a 26 mile beach run in 4 low?

If your overheating the tranny in 2hi or 4hi,then yes run it in 4low at 10-15mph,just leave the tranny in O/D.

I would not leave it in O/D
I would at most run it in Drive with the O/D locked out but I would watch it closely for gear hunting ,lots of shifting
if it is then drop it to 2nd and let the engine run at 3000 rpms if needed ,I do it all the time so I know it will not hurt
I ran for close to 700 miles turning 3000 rpm ,now granted it was on the highway and in 2wd but the rpm did not hurt any thing

I was running about 25 MPH at 2500 in 4 hi and 25 MPH at 1500-2000 in 2 HI

And it was about 85 out that day

dieselenthusiast · **Posted:** Mon Sep 15, 2008 10:28 pm

I’m selling my 30 foot Travel Trailer and buying a small travel trailer to pull behind the KJ. However, my KJ did not come with a hitch. So my plans are to use the Rock Lizard rear bumper with the built-in hitch receiver. What types (brands) of aftermarket transmission coolers can I add to my 42RLE? I wish someone would make an aluminum pan cover, but they probably wont.

jsc7002 · **Posted:** Tue Sep 16, 2008 12:08 am

I have a Hayden Ultra-Cool, I think I paid about $40 for it

Pablo · **Joined:** Thu Feb 02, 2006 10:06 pm **Posts:** 1201

This maybe silly of me, but have you checked to make sure the electric fan is still working? Per other peoples post's here, sometimes they get gummed up. Also, is the heat exchanger (if you have one) clean and not covered in mud?

You can also buy tranny coolers for the KJ off of Jeepin By Al's site. That man has about everything... (at least a good place to look first).

sleeve84028 · **Posted:** Tue Sep 16, 2008 1:13 pm

Here's a link to the cooler...

Trans cooler You can not go wrong with additional cooling. Especaially when it comes to a vehicle that gets worked hard.

dieselenthusiast · **Posted:** Tue Sep 16, 2008 5:31 pm

sleeve84028 wrote:

Here's a link to the cooler...

Trans cooler You can not go wrong with additional cooling. Especaially when it comes to a vehicle that gets worked hard.

THANK YOU, I just placed the order............................. Is there anything else that I can add to keep the trany fluid cooler?????

tjkj2002 · **Posted:** Tue Sep 16, 2008 7:36 pm

dieselenthusiast wrote:

sleeve84028 wrote:

Here's a link to the cooler...

Trans cooler You can not go wrong with additional cooling. Especaially when it comes to a vehicle that gets worked hard.

THANK YOU, I just placed the order............................. Is there anything else that I can add to keep the trany fluid cooler?????

Just remember that the KJ's with the 42RLE has a stand alone trans cooler,unlike the KJ's with the 45RFE that has the main trans cooler that is in the passenger side tank of the radiator(and HD cooling adds a AUX cooler).Just replacing the stand alone cooler will not gain you much since the cooler will not be able to handle temp spikes that the in-radiator cooler alone will do since that is the radiators main job of controlling temp spikes.I would get a '02 radiator(one for a 45RFE KJ,it will fit),you will have to mod the trans cooler lines,not hard,and then add a AUX cooler of your choice and you will never overheat your 42RLE unless your engine severly overheats also.

dieselenthusiast · **Posted:** Tue Sep 16, 2008 7:50 pm

tjkj2002 wrote:

I would get a '02 radiator(one for a 45RFE KJ,it will fit),you will have to mod the trans cooler lines,not hard,and then add a AUX cooler of your choice and you will never overheat your 42RLE unless your engine severly overheats also.

What would the price be for a new '02 replacement radiator?

myjeepwalks · **Posted:** Tue Sep 16, 2008 8:40 pm

dieselenthusiast wrote:

tjkj2002 wrote:

I would get a '02 radiator(one for a 45RFE KJ,it will fit),you will have to mod the trans cooler lines,not hard,and then add a AUX cooler of your choice and you will never overheat your 42RLE unless your engine severly overheats also.

What would the price be for a new '02 replacement radiator?

Think i paid like $180 for mine. I also have trans temp guage with the sender in the hot line going into the cooler. (eventualy i will install it in the pan). Any way my trans will get as hot as 210F in the summer with the o/d. If i lock out o/d it will drop around 180F. A few weeks ago when i was in OBX i had it in 4L, a/c on, tires aired down to 20psi, 6 people in the kj, 90 degree weather, and DEEP sand. Trans temp light never came on and trans temp was hovering around 230F on my temp guage. Again my guage reads the hot line coming out of the trans. I dont know how cool it gets once it goes through the cooler and back in the trans. I plan to add and aux cooler in the near future, just haven't gotten around to it yet.

Does anyone know what the trans fluid temp has to hit before the light comes on?

jason thompson · **Posted:** Tue Sep 16, 2008 9:04 pm

Just some FYI if you are looking at tranny coolers
-they should always be secondary ,behind the OE cooler
-the number of passes does not always make it better ,surface area is where it counts, the oil will only cool so much but to cool it must loose its heat the heat has to get away if it has to many passes and not enough surface area it will help less than one with the same surface area but less passes ,there is a magic number when you look at surface area size of tube and number of passes which I have no clue how to figure out
I just know that I read about it when I was looking in to getting one

here are some from Flex a lite
http://www.flex-a-lite.com/auto/html/tr ... olers.html

sleeve84028 · **Posted:** Wed Sep 17, 2008 8:16 am

To continue thoughts on coolers: The cooler works just like a radiator would. I'll assume that most of us know how they function. But figured this could be a fun topic to discuss so...

Basic principal of heat transfer: Heat engergy always moves to a colder surface.

So in the case of an auxillary cooler, the hot transmission oil is heating up the tube/fin cooler. This function pulls heat out of the fluid. Now the problem is that the cooling tube are hot. So cooling fins are added. The fins job is to capture cool air moving past the cooler. The heat trapped on the cooling unit is then moved to the surrounding air. Now if you have too many fins, the air flow isn't sufficient and limits the cooling capaibility of the fins. On the flip side, if the fin spacing is too large than the cooler is loosing out on some heat transfer capability. Interesting stuff right there...

To the point of "spike" heat absorbtion: The radiator coolers do a great job at pulling spike loads out of the fluid because the surface area is much larger than the smaller aux cooler units. So the heat energy can be spread out over a larger metal cooling surface. If that same energy was to be processed through the smaller cooler, the heat spike would overwhelm the capability of the unit. While still pulling some heat out - the cooler would send heated fluid back into the transmission.

Quite the balancing act for sure but a fun topic to think about.

Tranny Temp

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