I probably asked this before, but I still don't get it.
Why does 4-HIGH on a steep climb lead to possible overheating, but 4-LOW does not?

From what I understand the transmission overheats from too much shifting.
But what if you are just staying at a constant speed and staying in the same gear?
Why would 4-HIGH on a steep climb cause overheating if the transmission is not shifting?

There must be some other factor besides excessive shifting that causes the tranny to overheat???

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2007 Jeep Liberty Sport
Not Just Red..............Inferno Red !
Automatic, 4WD
Mopar Skids, Tow Hooks

The torque converter heats up.. In 4 low, the rpms are lower which means the torque isnt slipping as much...

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I refer you to this thread that covers the 4-low question near the end

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Nope. Still don't get it.
Say you're in 4-HIGH on Flat Ground staying in 2nd Gear.
What's different when you're in 4-HIGH on a Steep Grade staying in 2nd Gear?

_________________
2007 Jeep Liberty Sport
Not Just Red..............Inferno Red !
Automatic, 4WD
Mopar Skids, Tow Hooks

The torque coming out of the tranny is multiplied by 2.73. Is it harder for you to go up a hill on a bike in the highest gear, or the lowest gear? Putting the tcase in 4low makes it easier on the tranny and tcase.

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Lost #007082
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It makes sense that it's harder for the Jeep to go up hill, but what exactly causes the heat in the transmission?
Isn't slipping of the torque converter the only thing that causes a transmission to overheat?
So is there just more slippage at the torque converter if in 4-HIGH as compared to 4-LOW when going uphill?

_________________
2007 Jeep Liberty Sport
Not Just Red..............Inferno Red !
Automatic, 4WD
Mopar Skids, Tow Hooks

yes most of the heat is from the slipping of the torque converter.

first, theres no way you are going to be in second gear in 4high going up a steep hill. to keep it from downshifting into 1st you would have to climb at probably 20mph at least and you would look like you are in a toyota truck commercial, ( you know everyone just does 60 and slideways down all dirt roads huh)

its easy, just think of having a manual, the difference in lo range and hi is very similar to the difference between running up a hill in first gear and not having to slip the clutch (lo range/with not much slip) or tryin to climb a hill in 2nd or 3rd and having to slip the clutch to keep it from stalling (hi range/loads of torque converter slip)

if this explanation doesnt work, im sure i can clarify my point with any questions, but its a pretty basic concept.

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Youve just got to understand how a tranny works to get that.

Like I said, if the rpms of the engine are HIGHER, that means the torque converter will need to slip more(more heat). If the tcase is in LOW, then the engine rpms do not need to be as high to move the jeep. Thus the torque converter does not need to slip as much.

The tranny changing gears also makes alot of heat.

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Current Jeep: 2004 Jeep Liberty
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Lost #007082
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If you quickly but lightly rub two sticks together you won’t be able to make fire. But if you rub them with sufficient force you will get smoke and embers from the heat generated from the increased friction.

The same thing happens with your Jeep. Driving up and over objects puts much more resistance on the drive train resulting in potentially harmful levels of heat.

Gearing down creates a mechanical advantage that allows the drivetrain components to turn more easily resulting in lower transmission temperatures.

The difference between second gear in 4H and 4L is the degree of mechanical advantage. As Jeepjeepster indicated, the mechanical advantage of second gear in 4L is 2.73 times greater than second gear in 4H resulting in proportionately less heat.

The issue is not the torque converter per se. You should gear down into 4L even if you are driving a manual transmission for steep climbs.

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William C Montgomery
The Truth About Cars
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OK let me try
The trany over heats for several reasons
1-slipage 2-load and more load = more slipage that is how it shifts gears ,slipage
you can put an auto into first ,#1 gear, and it will slip less and never shift
got this so far?

OK now on to T-case ,wich is a totaly seprate unit from the trany
in 4 hi you go from power to 2 wheels to power to 4
this = twice as much traction with the same power
in 4 lo you get a gear reduction of 2.71 to 1
This means that when you compare your engine power from 4hi to 4lo ,in 4lo you have close to 600hp to move the same 4500# rig

Now on to climbing a hill
when you climb a hill you want to go as slow as you can in hi range ,2wd or 4wd you can not go slow and have the needed power so something has to slip
that would be the trany that will slip even in first it will slip or you will go to fast
now in 4lo it reduces your gearing by 2.71 making it so you can go both slower and have the power needed to climb the hill

If after this you still do not under stand I can only think of 2 things
1 you are just being a jackass or 2 you need to go out with a group and find out for your self
I can tell you this how ever
EVERY trail that I lead/guide the rule is this
"at the trail head put it in 4lo and leave it there" "if you have an auto put it in first and leave it there"
I have never seen a hill on any of "my trails" that could e safely climbed in 4hi

Take it easy now.. Seems like he is really trying to understand what is going on.

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I hope so
I know that some people like to
"push the issue" if they think that their way is the right way

The little light bulb in my head is dimly lit now.
Your explanations help a lot.
I think part of what was screwing me up is that when I was talking about a steep hill I wasn't thinking steep enough.
The part where you described how 4-HIGH or 2-HIGH would not let you go slow enough to keep the tranny from slipping finally helped it make sense to me.

The vision I had in my head was a flat forest road with switchbacks climbing up a mountain. I wasn't thinking of rock climbing.
So I guess if it was a road where I could go a steady, somewhat high speed with minimal shifting 4-LO wouldn't be necessary.
But if the road was very steep and I had to go real slow, and climb over potholes, rocks, fallen branches, etc then I would need the low gearing of 4-LOW to avoid a slipping transmission.

_________________
2007 Jeep Liberty Sport
Not Just Red..............Inferno Red !
Automatic, 4WD
Mopar Skids, Tow Hooks

Kinda yes and kinda no

The best way to look at the use of 4wd and off road is this
98.5% of the time
If you need 4wd because of lack of traction off road then you should probably be in 4lo
sure if you are running for miles down a muddy road that is FLAT then 4hi is ok
but if you can not go over 10 mph COMFORTABLY then you should be in 4lo

I NEVER use 4hi in my TJ it is 2wd or 4lo
In the KJ it is 2wd or 4hi FULLTIME mode ,when it is raining realy bad out and because it is safer that way
but on the trail it is 4lo all the time every time

Ok. Thanks. It's making more and more sense now.
I need to get out there and get some more experience.

_________________
2007 Jeep Liberty Sport
Not Just Red..............Inferno Red !
Automatic, 4WD
Mopar Skids, Tow Hooks

Thats right Cash. I usually use 4low if I know Im not going to be getting over 10mph for along time. Rock crawling, slow hill climbing, thats when you use 4low.

If you maintain a good speed, the tranny should be ok as long as you dont let it shift alot. Its usually best to manually shift the tranny and hold it in the gear that works out best for the speed you are going when going up a hill.

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LOST KJ'S
Where are you going???
Current Jeep: 2004 Jeep Liberty
-Atlantic Blue
-Air Ride Rear Suspension ; OME/Rustys Lift ; Powertrax Locker ; Moog Lower Ball-Joints ; 245/70/16 Yokohama Geolander A/T-S's on MOABS ; Flowmaster 50 SUV
Lost #007082
http://www.cardomain.com/id/jeepjeepster