42RLE Transmission Temperatures?

LONGJP2 said:
If you didn't know the temp., you probably wouldn't care.
Just change the fluid more often.
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Little confused about this one…. I cared about my transmission temm prior to the temp senor install but it was always just a “hope I’m not heating my transmission up on these rocks”

I agree with changing the fluid more often, but that doesn’t remove the chance of ruining a transmission from a one time high heat experience does it?
 
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Irun said:
For those of you running a temperature gauge on your 42RLE, what temperatures do you normally see on the trail?
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Define temperature:). On trail, the correct reading will be from the pan. Not in the input or output lines. Output lines will report too high, return to transmission too low.
It is not supposed to run at beyond 180F, it impacts the lifespan of your transmission if you exceed. It needs to run between 170F and 180F, per the technical manual, as measured in the valve body sensor (very very close to pan sensor when driving slow). It does NOT like to run hot at all.
First thing I would do (and I did) running a rig with 42RLE is to install external cooler (I used the derale electric one). It is not ideal, and it does not guarantee that transmission does not cross 180F ever ever, but it is very close to doing it. At highway speeds (80MPH, 4.56 gears and 31 tires, Houston Texas 100F) the transmission is around 160F/170F, not beyond this.
 
Bowhunter said:
Little confused about this one…. I cared about my temp pipe to the temp senor install but it was always just a “hope I’m not hearing my transmission up on these rocks”

I agree with changing the fluid more often, but that doesn’t remove the chance of ruining a transmission from a one time high heat experience does it?
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The TCM does not shut down the transmission when overheating (unlike in more modern cars), as a result you do damage your transmission when overheating. If there is one thing that 42RLE hates most, is the overheat. It needs to have external cooler, you cannot rely on just the cooler in the radiator.
 
Bowhunter said:
Bumping this up again because I’m about to head out and try some rock crawling in warm/hot ambient temps.

From my research people are saying the manuals says 150-200 is normal. But at what point do you need to stop and try to cool it down?

And how do you cool the transmission temp down if you’re in the middle of a crawling trail that you are unable to get speed to get more air through the radiator? Stop and let it idle in N or P?
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200F is not normal. Normal is when you read from pan at slow speeds under 180F. If you read 180F on highway speeds, it is little high. I have external Derale cooler, so never seen above 180F, and 185F in a very special case (traffic jam uphill going up very very slow - almost no airflow to cool, radiator running very hot and external electric cooler not kicking in yet)
 
TexasTJ2004 said:
Define temperature:). On trail, the correct reading will be from the pan. Not in the input or output lines. Output lines will report too high, return to transmission too low.
It is not supposed to run at beyond 180F, it impacts the lifespan of your transmission if you exceed. It needs to run between 170F and 180F, per the technical manual, as measured in the valve body sensor (very very close to pan sensor when driving slow). It does NOT like to run hot at all.
First thing I would do (and I did) running a rig with 42RLE is to install external cooler (I used the derale electric one). It is not ideal, and it does not guarantee that transmission does not cross 180F ever ever, but it is very close to doing it. At highway speeds (80MPH, 4.56 gears and 31 tires, Houston Texas 100F) the transmission is around 160F/170F, not beyond this.
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I agree with most of that, but I don't know that I've ever seen the manual say what temp the fluid should be at, especially considering they didn't give us any way to measure it...although I haven't poured over the FSM for the 42RLE years like I have the earlier years. But then that it requires an aftermarket external cooler to get into the recommended range doesn't pass my sniff test. 220-ish seems to be the "generally accepted" temp to stay under, which is achievable w/o a cooler. I'm interested to find the temp sensor in the wiring diagrams, because after being on jeep forums for a minute or two, I've never heard it mentioned.

I am in no way suggesting coolers aren't a good idea, I run one in my 97 and it dramatically lowered my temps. Lower is better.
 
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hear said:
I agree with most of that, but I don't know that I've ever seen the manual say what temp the fluid should be at, especially considering they didn't give us any way to measure it...although I haven't poured over the FSM for the 42RLE years like I have the earlier years. But then that it requires an aftermarket external cooler to get into the recommended range doesn't pass my sniff test. 220-ish seems to be the "generally accepted" temp to stay under, which is achievable w/o a cooler. I'm interested to find the temp sensor in the wiring diagrams, because after being on jeep forums for a minute or two, I've never heard it mentioned.

I am in no way suggesting coolers aren't a good idea, I run one in my 97 and it dramatically lowered my temps. Lower is better.
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Blaine said the same thing, 220-230 was acceptable but he does like to see it a bit lower

One thing to me that makes low 200s-220 seem normal is that the coolant (that is also in the radiator) ranges from 180 ish-220 ish so it seems to me the transmission would run about the same since it’s in the same radiator (temp transfer via convection)

If I didn’t have a brand new mopar radiator, I wouldn’t even be tearing this out and would just throw in a aux cooler

What kind of temp reduction did you see at slow speeds/off-roading when you added the aux cooler?
 
hear said:
I agree with most of that, but I don't know that I've ever seen the manual say what temp the fluid should be at, especially considering they didn't give us any way to measure it...although I haven't poured over the FSM for the 42RLE years like I have the earlier years. But then that it requires an aftermarket external cooler to get into the recommended range doesn't pass my sniff test. 220-ish seems to be the "generally accepted" temp to stay under, which is achievable w/o a cooler. I'm interested to find the temp sensor in the wiring diagrams, because after being on jeep forums for a minute or two, I've never heard it mentioned.

I am in no way suggesting coolers aren't a good idea, I run one in my 97 and it dramatically lowered my temps. Lower is better.
Click to expand...

You would be surprised, but the actually did provide us with a very rudimentary way of measuring the temps. The idea is that change in the level of the fluid is what reflects the temperature. There is a chart in the manual the describes the dependency between fluid level and temperature. If you buy some kind of special dipstick with calibration, you can actually read it in +/- 20F.
 
This is the chart that you supposed to be using per 42RLE manual. This is assuming that the fill was performed to factory defined levels.
As you can see, 220F is not even in the chart. Between 165F and under 200F is where can be per hot definition,
1687463342646.png
 
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Bowhunter said:
Blaine said the same thing, 220-230 was acceptable but he does like to see it a bit lower

One thing to me that makes low 200s-220 seem normal is that the coolant (that is also in the radiator) ranges from 180 ish-220 ish so it seems to me the transmission would run about the same since it’s in the same radiator (temp transfer via convection)

If I didn’t have a brand new mopar radiator, I wouldn’t even be tearing this out and would just throw in a aux cooler

What kind of temp reduction did you see at slow speeds/off-roading when you added the aux cooler?
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I had been running in the 180-200 range, although on some steep inclines I saw it shoot past 220. I figure it was being starved and nothing was going through the cooler. Then I rebuilt the thing....post rebuild, I was pushing 220F regularly, but even that comes with an asterisk. For one, it was balls hot when I completed my rebuild. Like 100F+. My test runs primarily consisted of driving to XJ buddy's house which is about 15 mins away to the east, with a little stop and go. No trouble on temps on the way there, but those were almost always from a cold start. We'd work on his stuff for a few hours, and then I'd drive home....west, directly into the sun. Same distance on the trip, but I would be pushing 220 by the time I got to my driveway. I chalked it up to the ridiculous DFW heat and the fact that the sun beating on the radiator heading west was possibly a factor, but also in the back of my mind I wondered if the new clutches were generating more friction heat because the clearance was less than what it was prior to the rebuild. But it was definitely hotter running after my rebuild.

Put the cooler in...I used a Hayden & mounted it in front of the radiator, plumbed post-radiator (meaning I left the existing cooling system intact & in use), and I don't think I've seen it get over 140F even once.
 
hear said:
I had been running in the 180-200 range, although on some steep inclines I saw it shoot past 220. I figure it was being starved and nothing was going through the cooler. Then I rebuilt the thing....post rebuild, I was pushing 220F regularly, but even that comes with an asterisk. For one, it was balls hot when I completed my rebuild. Like 100F+. My test runs primarily consisted of driving to XJ buddy's house which is about 15 mins away to the east, with a little stop and go. No trouble on temps on the way there, but those were almost always from a cold start. We'd work on his stuff for a few hours, and then I'd drive home....west, directly into the sun. Same distance on the trip, but I would be pushing 220 by the time I got to my driveway. I chalked it up to the ridiculous DFW heat and the fact that the sun beating on the radiator heading west was possibly a factor, but also in the back of my mind I wondered if the new clutches were generating more friction heat because the clearance was less than what it was prior to the rebuild. But it was definitely hotter running after my rebuild.

Put the cooler in...I used a Hayden & mounted it in front of the radiator, plumbed post-radiator (meaning I left the existing cooling system intact & in use), and I don't think I've seen it get over 140F even once.
Click to expand...

Thanks for the detailed info. I’m just going to order one since there is a high likelihood I’ll need one.

Do you by chance know the model number of the Hayden you used?
 
hear said:
Put the cooler in...I used a Hayden & mounted it in front of the radiator, plumbed post-radiator (meaning I left the existing cooling system intact & in use), and I don't think I've seen it get over 140F even once.
Click to expand...
The problem with radiators that are exposed to airflow in the radiator area, is that they actually cool too much in the winter. In the winter, the goal it try to heat the transmission to working range. Cooler that is directly exposed, will cause excessive cooling. Not really a problem here in Texas, but anyway.
 
BTW, with definition of overheat:
42RLE shift schedule in TJ does have a definition of overheat - it is ATF+4 at 240F or engine coolant at 244F.
I am pretty sure that none of us believes that engine coolant at let's say 240F is anything healthy for the engine, but the manual does not define let's say 238F transmission and 242F engine to be overheat.

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TexasTJ2004 said:
The problem with radiators that are exposed to airflow in the radiator area, is that they actually cool too much in the winter. In the winter, the goal it try to heat the transmission to working range. Cooler that is directly exposed, will cause excessive cooling. Not really a problem here in Texas, but anyway.
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yeah, this winter it did occur to me that there is probably a lower bound on the temp where the ATF is fully effective. Like it never got over 100F, and it wasn't even that cold. I guess I could plumb in a diverter valve but I already have enough failure domains.
 
Bowhunter said:
Thanks for the detailed info. I’m just going to order one since there is a high likelihood I’ll need one.

Do you by chance know the model number of the Hayden you used?
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https://www.amazon.com/gp/product/B000C3BBKS/?tag=wranglerorg-20

I know others are partial to the Derale installed under the jeep. That setup uses fan mounted on the cooler, but also doesn't block the radiator. I've had zero issues with engine temp so I feel like I made the right choice. YMMV.
 
hear said:
yeah, this winter it did occur to me that there is probably a lower bound on the temp where the ATF is fully effective. Like it never got over 100F, and it wasn't even that cold. I guess I could plumb in a diverter valve but I already have enough failure domains.
Click to expand...

In the winter, the engine radiator is supposed to heat the atf+4, trying to heat up the transmission. Lifespan of transmission depends on hours spent at each temperature. When you do a lot of short drives, it never had enough time to heat up, so it will not live long. If you run too hot, it will die prematurely.
This is why Derale electric is little better - it does not cool too much driving on highway at highway speeds, the airflow is modulated by sensor activating the fan, unlike Hayden, where the airflow depends only on speed of the vehicle.
 
TexasTJ2004 said:
The problem with radiators that are exposed to airflow in the radiator area, is that they actually cool too much in the winter. In the winter, the goal it try to heat the transmission to working range. Cooler that is directly exposed, will cause excessive cooling. Not really a problem here in Texas, but anyway.
Click to expand...

I’m located in an area that ranges from 105/110 ish in the summer to just below freezing in the winter. The jeep is a secondary recreational vehicle for me but I foresee rock crawling a fair amount in the cooler months.

The radiator mounted transmission cooler is by far most bang for your buck, vs $300+ on a derale with a fan. Is the low transmission temp with a rad mounted cooler more of an issue for guys that get much cooler (well below freezing, even into the negatives)?

One could buy a cheap hayden cooler, knowing that it’s not nearly as effective as say a setrab but then maybe you wouldn’t run into cool weather issues?
 
hear said:
https://www.amazon.com/gp/product/B000C3BBKS/?tag=wranglerorg-20

I know others are partial to the Derale installed under the jeep. That setup uses fan mounted on the cooler, but also doesn't block the radiator. I've had zero issues with engine temp so I feel like I made the right choice. YMMV.
Click to expand...

I was thinking something a bit smaller like this so you could fit it through the headlight opening (remove headlight) like others have done. Maybe a happy medium between hot weather cooling and low temp cooling

https://www.amazon.com/dp/B000C39CL8/?tag=wranglerorg-20
 
TexasTJ2004 said:
The problem with radiators that are exposed to airflow in the radiator area, is that they actually cool too much in the winter. In the winter, the goal it try to heat the transmission to working range. Cooler that is directly exposed, will cause excessive cooling. Not really a problem here in Texas, but anyway.
Click to expand...

Reading the B&M section in blue, it seems they may have at least some what addressed that issue? What are your thoughts?

This was on Amazon for BM 70268

IMG_3432.jpeg
 
TexasTJ2004 said:
I was not aware of that feature that they have. Seems like a pretty cool thing.
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I’ll probably give it a try!

I have this screen shot from Blaine a while back describing how to not air lock when adding a transmission cooler.

Any idea if this applies to these type of coolers were inlet and outlet are both at the bottom?

IMG_3441.jpeg


IMG_3326.jpeg
 
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