Improving the cooling on our TJs

[TexasTJ2004]

I did that method out of necessity so I could watch my temps driving my rig to Blaines before he added a bung. I don't recommend doing that to others because the sensor sticks out like a lollipop and can be snapped off (and cause a catastrophic failure). Also, placing the sensor there doesn't allow the Savvy skid plate to be installed.

You want the sensor to be protected like it is where Blaine places them.

For accuracy: I just realized that my previous post saying I shipped the Dorman pan to Blaine is incorrect. He did that work by dropping the pan when he had my rig. I later shipped Blaine an oil pan so he could add a bung for my turbo's oil return line. Sorry for the mixup.

In my case I am running the stock transmission skid plate that comes with Sport 2004. It protects the sensors because the sensor is above the transmission skid plate.
Savvy skid has higher clearance than stock, this is why you cannot do what I did - stock skid is like a shovel. .

 

[MikeE024]

In my case I am running the stock transmission skid plate that comes with Sport 2004. It protects the sensors because the sensor is above the transmission skid plate.
Savvy skid has higher clearance than stock, this is why you cannot do what I did - stock skid is like a shovel. .

Tbh I wouldn’t do it with the stock skid plate either. I can’t think of a reason that would outweigh my desire to minimize that fail point with minimal effort on my part.

And I try to do things so future mods will integrate well with previous mods.

 

[TexasTJ2004]

Tbh I wouldn’t do it with the stock skid plate either. I can’t think of a reason that would outweigh my desire to minimize that fail point with minimal effort on my part.

And I try to do things so future mods will integrate well with previous mods.

Maybe I am missing something. Take a look at this pic. I took the picture of my TJ from underneath.you can see that there is an engine oil pan skid plate (metal cloak), transmission skid plate (stock) and the transfer case skid plate (stock).
The sensor is between the transmission to the transmission skid plate, you can even see it. Yes, if I go over some bush and it will get into the gap between transmission skid plate to transmission oil pan, it will damage the sensor connector, but it is extremely unlikely to happen

 

[MikeE024]

Maybe I am missing something. Take a look at this pic. I took the picture of my TJ from underneath.you can see that there is an engine oil pan skid plate (metal cloak), transmission skid plate (stock) and the transfer case skid plate (stock).
The sensor is between the transmission to the transmission skid plate, you can even see it. Yes, if I go over some bush and it will get into the gap between transmission skid plate to transmission oil pan, it will damage the sensor connector, but it is extremely unlikely to happen

View attachment 478783

I don’t think it’s a misunderstanding, it’s just different philosophies

 

[TexasTJ2004]

Hayden 2791’with Derale 6 blade fan before installation.

 

[MikeE024]

Trailing in 4HI creates much more load on the transmission. Not healthy for it.

Can you explain your reasoning here? I’ve mostly been more than fine in 4hi. There’s just a threshold that I recently discovered regarding load equating to more heat than I prefer.

On my last trip to Big Bend, I put into 4L every time when i moved off the pavement into the trail. I have manual hubs in the front (conversion kit), so I kept the hubs unlocked in 4L, and locked them only when 4x4 was really needed (basically it is a 2L mode in some way). The trail was dry, so I had to lock the hubs only one time when i did the step on the Black Gap trail itself.

Many trails work much better with 2.72:1 than 4:1. We aren’t playing the same game, which is why I’ve been interested in a rubicrawler for the flatter and faster stuff.

The transmission temperature stayed relatively low, never reaching beyond 180F, so the derale cooler did not have to kick in.

That’s great to know bc that’s about the temps I’d see if I added 2.72:1

I run anywhere from 158-185* in 4low even when working hard. I go to low when 4hi reaches 200* or less. I’ve run hotter but not for long.

 

[TexasTJ2004]

Can you explain your reasoning here? I’ve mostly been more than fine in 4hi. There’s just a threshold that I recently discovered regarding load equating to more heat than I prefer.

The moment that you go into low gear, the load on the engine and the transmission changes for the following reasons:
For every one rotation of transmission output shaft, the travel that the vehicle needs to make is 2.72 (in your case 4) times smaller.
This basically means that the engine and transmission are doing much less work, which is defined by moving the car. Think of rotating the wheels as of fastening a nut - the moment that you take longer wrench, it becomes much easier to fasten the bolt. The torque that is delivered to wheels is in low gear is multiplied by factor of low gear (4 times in your case).
The torque that the wheels need on trail at speed of let’s say 8 mile per hour is pretty much constant, but in low gear gear the transmission output needs to provide 2.72 time (in my case) less torque, it is pretty much does not need to work hard at all.
BTW, the main reason why TJ rubicon has Dana 44 in front is the fact that Dana 30 ring and pinion is to weak to deal with amount of torque that is provided with 4:1 transfer case ratio.
With my manual hubs in the front, I use 4L with unlocked hubs all the time when I don’t want to load the transmission in slow speeds, if I need to reverse on a steep driveway, or if I need to backup a trailer of if I need to climb something like sidewalk for example.

 

[MikeE024]

The moment that you go into low gear, the load on the engine and the transmission changes for the following reasons:
For every one rotation of transmission output shaft, the travel that the vehicle needs to make is 2.72 (in your case 4) times smaller.
This basically means that the engine and transmission are doing much less work, which is defined by moving the car. Think of rotating the wheels as of fastening a nut - the moment that you take longer wrench, it becomes much easier to fasten the bolt. The torque that is delivered to wheels is in low gear is multiplied by factor of low gear (4 times in your case).
The torque that the wheels need on trail at speed of let’s say 8 mile per hour is pretty much constant, but in low gear gear the transmission output needs to provide 2.72 time (in my case) less torque, it is pretty much does not need to work hard at all.

Thanks for explaining that. The 2.72:1 would make me much happier when I’m wheeling in more spirited situations and when coming down trails.

With my manual hubs in the front, I use 4L with unlocked hubs all the time when I don’t want to load the transmission in slow speeds, if I need to reverse on a steep driveway, or if I need to backup a trailer of if I need to climb something like sidewalk for example.

For the most part, 2low it doesn’t really interest me, but it’s nice to have as an option. I’ve been in a bunch of steep loose trails and want the control that 4wd gives me even on decent. 2wd would be really stupid with trails like that especially when cliffs and drop-offs are involved. In 2wd you can brake the same going down hill, but you can’t drive yourself out of trouble nearly as well if you are pushing straight and losing traction.

But on the street I sure do love 2HI feeling like it’s driving on rails.

 

[TexasTJ2004]

Many trails work much better with 2.72:1 than 4:1. We aren’t playing the same game, which is why I’ve been interested in a rubicrawler for the flatter and faster stuff.

Adding rubicrawler sounds like an amazing option. I am thinking about as well, but I have a couple of problems with it.
If you add rubicrawler with 4:0 transfer case, the add ons that you get area
1) 2:72 with true 2L when transfer case in 2HI
2) true 4L 2.72 when transfer case in 4HI
3) around 11:1 crazy ratio when rubicrawler and Rubicon transfer case both engaged in LOW.

2.72 option is a must in my opinion, because you do need on a lot of non rocky trails and especially on sand - 4:1 is little too slow on soft sand.

The 11:1 although sounds amazing, seems to be a very risky from the perspective of stocks driveshafts, stock ring and pinion, stock shafts etc. You are multiplying the amount of torque delivered to the wheels by factor of 2:72 compared to stock, which is really a lot for TJ Dana 44 stuff. I would not do that w/o highest quality chromoly shafts and aftermarket driveshafts. If you are really careful with gas pedal when in 11:1, then it might be safe, but it would be too scary for me personally.

In your case I would see the rubicrawler as something with which you can enjoy both worlds 2.72 2L, 2.72 4L, and 4 4L. Completely safe to use it that way as everything is designed to 4:1 ratio already.


I personally have TJ sport, so my transfer case is 2.72, so adding rubicrawler to it will make it 2.72 and 7.4. In order to safely use 7.4 I will need the SYE, double cardan aftermarket driveshaft and finish installing my chromoly shafts into Rear Dana 44 that I have. However, my front HP30 from XJ, has little too weak ring and pinion for anything like 7.4 ratio, even with manual hubs and chromoly shafts that I have.

 

[MikeE024]

Adding rubicrawler sounds like an amazing option. I am thinking about as well, but I have a couple of problems with it.
If you add rubicrawler with 4:0 transfer case, the add ons that you get area
1) 2:72 with true 2L when transfer case in 2HI
2) true 4L 2.72 when transfer case in 4HI
3) around 11:1 crazy ratio when rubicrawler and Rubicon transfer case both engaged in LOW.

2.72 option is a must in my opinion, because you do need on a lot of non rocky trails and especially on sand - 4:1 is little too slow on soft sand.

The 11:1 although sounds amazing, seems to be a very risky from the perspective of stocks driveshafts, stock ring and pinion, stock shafts etc. You are multiplying the amount of torque delivered to the wheels by factor of 2:72 compared to stock, which is really a lot for TJ Dana 44 stuff. I would not do that w/o highest quality chromoly shafts and aftermarket driveshafts. If you are really careful with gas pedal when in 11:1, then it might be safe, but it would be too scary for me personally.

In your case I would see the rubicrawler as something with which you can enjoy both worlds 2.72 2L, 2.72 4L, and 4 4L. Completely safe to use it that way as everything is designed to 4:1 ratio already.


I personally have TJ sport, so my transfer case is 2.72, so adding rubicrawler to it will make it 2.72 and 7.4. In order to safely use 7.4 I will need the SYE, double cardan aftermarket driveshaft and finish installing my chromoly shafts into Rear Dana 44 that I have. However, my front HP30 from XJ, has little too weak ring and pinion for anything like 7.4 ratio, even with manual hubs and chromoly shafts that I have.

I would have three usable options and a fourth unusable option.

I would do it to have both 2.72:1 and 4:1 for trails.

Tbh, I wouldn’t want 7.4:1, so I probably wouldn't combine it with a 231 if that’s the best low option.

Spent a day in fine sand at Sand Hollow and would have enjoyed 2.72:1

 

[NashvilleTJ]

The moment that you go into low gear, the load on the engine and the transmission changes for the following reasons:
For every one rotation of transmission output shaft, the travel that the vehicle needs to make is 2.72 (in your case 4) times smaller.
This basically means that the engine and transmission are doing much less work, which is defined by moving the car. Think of rotating the wheels as of fastening a nut - the moment that you take longer wrench, it becomes much easier to fasten the bolt. The torque that is delivered to wheels is in low gear is multiplied by factor of low gear (4 times in your case).
The torque that the wheels need on trail at speed of let’s say 8 mile per hour is pretty much constant, but in low gear gear the transmission output needs to provide 2.72 time (in my case) less torque, it is pretty much does not need to work hard at all.
BTW, the main reason why TJ rubicon has Dana 44 in front is the fact that Dana 30 ring and pinion is to weak to deal with amount of torque that is provided with 4:1 transfer case ratio.
With my manual hubs in the front, I use 4L with unlocked hubs all the time when I don’t want to load the transmission in slow speeds, if I need to reverse on a steep driveway, or if I need to backup a trailer of if I need to climb something like sidewalk for example.

All that may be true, but as I understand it that is not the main reason for the additional tranny heat. When running slow in high range, the engine is operating at a much lower rpm than when in low range at the same speed. The impact of the lower rpm is that the torque converter does not lock up as it does at higher rpms. The resulting slippage causes the additional heat in the transmission fluid, and therefore the tranny.

When you are running trails at the same speed, but in low range, the rpm to the torque converter is higher, allowing the torque converter to lock up, reducing slippage, and therefore reducing heat.

 

[MikeE024]

All that may be true, but as I understand it that is not the main reason for the additional tranny heat. When running slow in high range, the engine is operating at a much lower rpm than when in low range at the same speed. The impact of the lower rpm is that the torque converter does not lock up as it does at higher rpms. The resulting slippage causes the additional heat in the transmission fluid, and therefore the tranny.

When you are running trails at the same speed, but in low range, the rpm to the torque converter is higher, allowing the torque converter to lock up, reducing slippage, and therefore reducing heat.

I talked to someone who I trust about this yesterday. If I understood him correctly, I wasn’t causing any damage to the transmission by running at 200* in 4hi.

I’ve been wondering if your explanation also explains why the transmission heats up in rush hour traffic.

 

[NashvilleTJ]

I talked to someone who I trust about this yesterday. If I understood him correctly, I wasn’t causing any damage to the transmission by running at 200* in 4hi.

I’ve been wondering if your explanation also explains why the transmission heats up in rush hour traffic.

200* tranny is not a problem. You really don’t get into trouble until you start consistently getting above about 230. I believe it was Blaine who told me that when I was redoing my tranny and steering cooling systems earlier this year.

And yes, that is why your tranny heats up in rush hour traffic.

 

[TexasTJ2004]

All that may be true, but as I understand it that is not the main reason for the additional tranny heat. When running slow in high range, the engine is operating at a much lower rpm than when in low range at the same speed. The impact of the lower rpm is that the torque converter does not lock up as it does at higher rpms. The resulting slippage causes the additional heat in the transmission fluid, and therefore the tranny.

When you are running trails at the same speed, but in low range, the rpm to the torque converter is higher, allowing the torque converter to lock up, reducing slippage, and therefore reducing heat.

I don’t know how the 3 speed in 1997-2002 operated, but in 42RLE in 2003-2006 the torque converter lockup is controlled electronically. If overdrive is disabled by driver using the button, then the link torque converter locks up at 3rd gear already. If the overdrive is enabled, then it will lockup only in overdrive. 1st and 2nd gear will not allow lock up.
Unless you are in 3rd gear at least, it will never lockup. On trail in HI, you will be most likely in 2nd gear, so no lockup.
If you are in LOW with overdrive enabled, I think that you will most likely never get locking up on the converter, because you will not hit the overdrive on trail.

 

[TexasTJ2004]

I talked to someone who I trust about this yesterday. If I understood him correctly, I wasn’t causing any damage to the transmission by running at 200* in 4hi.

I’ve been wondering if your explanation also explains why the transmission heats up in rush hour traffic.

200F will not cause damage, but it is generally not a desired transmission temperature. You want it ideally between 170F to 180F, this will make the life of transmission long and healthy. That is ideal range for it.
TCM considers overheat to be like 230F.

 

[NashvilleTJ]

I don’t know how the 3 speed in 1997-2002 operated, but in 42RLE in 2003-2006 the torque converter lockup is controlled electronically. If overdrive is disabled by driver using the button, then the link torque converter locks up at 3rd gear already. If the overdrive is enabled, then it will lockup only in overdrive. 1st and 2nd gear will not allow lock up.
Unless you are in 3rd gear at least, it will never lockup. On trail in HI, you will be most likely in 2nd gear, so no lockup.
If you are in LOW with overdrive enabled, I think that you will most likely never get locking up on the converter, because you will not hit the overdrive on trail.

Interesting. It’s been a while since I’ve driven a 42’.

Another thought: Does the 42’ torque converter slip more at lower RPM’s or at higher RPM’s?

 

[MikeE024]

I don’t know how the 3 speed in 1997-2002 operated, but in 42RLE in 2003-2006 the torque converter lockup is controlled electronically. If overdrive is disabled by driver using the button, then the link torque converter locks up at 3rd gear already. If the overdrive is enabled, then it will lockup only in overdrive. 1st and 2nd gear will not allow lock up.
Unless you are in 3rd gear at least, it will never lockup. On trail in HI, you will be most likely in 2nd gear, so no lockup.
If you are in LOW with overdrive enabled, I think that you will most likely never get locking up on the converter, because you will not hit the overdrive on trail.

@NashvilleTJ my guess is that it slips more at lower RPMs. What I've seen out in the trail makes sense after reading your explanation about the torque converter.

@TexasTJ2004 in 4low with the 4:1 gearing, the 42rle is quick to jump to overdrive (and lockup), which is the only time low doesn't feel miserable (jerky) in the rocks. I believe that's the main reason why the trans temp drops by about 30*.

On inclines that are too fast for 4:1, I rarely go fast enough in 4hi to get it to lockup in 3rd even though I run OD off. I'm hopeful that running the 2.72:1 option in faster trails would keep the transmission temps more around 185*.

 

[Rickyd]

@NashvilleTJ my guess is that it slips more at lower RPMs. What I've seen out in the trail makes sense after reading your explanation about the torque converter.

@TexasTJ2004 in 4low with the 4:1 gearing, the 42rle is quick to jump to overdrive (and lockup), which is the only time low doesn't feel miserable (jerky) in the rocks. I believe that's the main reason why the trans temp drops by about 30*.

On inclines that are too fast for 4:1, I rarely go fast enough in 4hi to get it to lockup in 3rd even though I run OD off. I'm hopeful that running the 2.72:1 option in faster trails would keep the transmission temps more around 185*.

Keep in mind that its generally recommended you use your doubler after engaging low in the transfercase.this is to reduce stress on the tcase as input torque will skyrocket with a doubler.

How you intend to use it can cause problems

 

[TexasTJ2004]

Interesting. It’s been a while since I’ve driven a 42’.

Another thought: Does the 42’ torque converter slip more at lower RPM’s or at higher RPM’s?

I don’t know. It is completely electronically controlled with TCM controlling every aspect of Torque Converter behavior.

 

[TexasTJ2004]

@NashvilleTJ my guess is that it slips more at lower RPMs. What I've seen out in the trail makes sense after reading your explanation about the torque converter.

@TexasTJ2004 in 4low with the 4:1 gearing, the 42rle is quick to jump to overdrive (and lockup), which is the only time low doesn't feel miserable (jerky) in the rocks. I believe that's the main reason why the trans temp drops by about 30*.

On inclines that are too fast for 4:1, I rarely go fast enough in 4hi to get it to lockup in 3rd even though I run OD off. I'm hopeful that running the 2.72:1 option in faster trails would keep the transmission temps more around 185*.

if you want to force the lockup earlier, just disable the overdrive. Then the lockup will happen much earlier, in 3rd gear. This is what I do on trails in 4L.
You have 4:1, so it will be a problem.
BTW, what gearing do you have? I have 4.56 and running 31 inch tires, I still think that 4:88 would do a better job with 31s and 42RLE do to extremely low overdrive ratio.