2hi and long mountain climbs, danger of burning up auto transmission??
 

Hey guys, just recently got my 2008 sahara and am loving it. The thing is I have been reading about all the over heating issues. I am going to the mountains tomorrow and pretty much am going to be climbing a lot of forest service roads, some a little technical, but 2hi should handle everything. I have read a ton of horror stories of 4hi and going 20 and under up any grade. Will 2hi (without OD obviously) cause the same problem? I know I could throw it into 4lo and be safe, but there is 1 long, steep, tarmac hill I need to get over north of Helen, and this can not be done in 4lo.

Stay out of 4-wheel unless you need it as it produces more load on the transmission. When in 2-hi, you should select a lower gear if you're ascending long grades. My rule of thumb is to keep the RPM in the 2500-3000 range at the given road speed I need to achieve to allow the engine coolant and transmission fluid to cycle and dissipate heat quick enough.

Reduce shifting whenever possible. If you notice the transmission gear-hunting, or if it is shifting a lot because of constant changes in throttle input and speed, it's a good idea to "lock out" in whatever gear you need. For instance, if the trans is hunting between 1-2 on a long and steep winding grade, lock out in 1st, reduce speed, and keep your engine RPM in that desired range for good cooling. Same can be done in any gear, and for highway climbs, shifting to 3, or using an O/D lockout button (can't remember if the JK has one or not) is a good idea.

If you smell hot, or get a warning light for the transmission temp, pull over but do not shut off the vehicle. Allowing the vehicle to idle lets fluid cycle through the transmission and dissipate heat faster. The last thing you want to do is shut of a smoking hot automatic trans and let hot fluid bake with the internals.

If I can't run at least 2,000 RPM while locked out in 1st gear on a mildly steep and technical climb, then I'd suggest it's time for 4lo and to run a more constant, higher rpm for better cooling and mechanical advantage.

As a general rule, 4lo is for speeds <15mph on unpaved or loose road surfaces.

4hi is generally for flat treacherous loose/unpaved road surfaces where city-highway speeds are still achievable but where additional traction is needed for vehicle stability.

2hi is for everything else.

Going up a long grade with the torque converter unlocked will generate a lot of heat in the automatic transmission.
The torque converter will not lock with the shift lever in 1 or 2.
The 3.8L/42RLE has an inadequate transmission cooler.
You should install an aux transmission cooler. Turning on the A/C may force the fan to come on, drawing more air through the aux cooler.
Consider getting a gauge that will read transmission temp through the OBDII port.

In 2hi and 4hi your torque converter may never lock if you can't go fast enough to reach 3rd gear. Going to 4lo will allow the transmission to shift into 3rd and lock the converter without having to go fast. I have done this and have seen the trans temp immediately begin to fall.

It won't take much for you to overheat the transmission unless you take steps to prevent it.

I have installed an aux cooler, and have done this: https://www.jk-forum.com/forums/modi...trofit-235132/
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Awesome, thanks for all the info fellows. I plan on installing the Auxiliary transmission cooler asap, but I can't do it by tomorrow. The main thing I was worried about is the long ascent up the mountain which is nothing but tarmac that is curvy as can be, so you can't get up to speed. When does 3rd gear kick in while its in 2hi? After that I am going to drop it into 4 low and climb the dirt road to the top of another mountain. Around where I live there hills all over the place so I find that leaving OD off is mandatory going up to 65 mph, otherwise its jumping all over the place. I start the Jeep and hit the OD button right away.

Doesn't the torque converter lock up around 40-45mph in most 4-speed autos (provided that you're able to reach 3rd gear)?

I don't know about other transmissions.
My 42RLE will lock up a lot slower than that if the load is light.

In 4lo, I recall it being locked by 10 mph.

Thanks for the tips guys. Went to the mountains and did some pretty knarly trail climbing (for this noob). I either had it in 2hi or 4lo the whole time. I really did not see where I would have needed 4 hi as it was wayyyy... to fast, even for the forest service roads around here (plenty of small rocks that will knock the fillings out of you teeth if you go to fast.) I never did have the heat light come on and it was a long........... slow climb on the technical trail. I felt bad taking my new jeep on a trail like that, felt like I abused her, lol.

In my transmission class we are currently learning about lock up torque converters and have learned that you must be in third gear before lock up on a torque flight transmission you have to have torque multiplication at low speed so yeah you usually go into 3rd around 45 mph plus you cannot have excessive throttle or the safety lock up valve will not allow it go in

Sorry to get off topic, but can you PM me where you went. I have been looking for more trails in Georgia.

Somewhat on topic, not meant to hijack... for spring break I'll be heading up to Vail with my son for some skiing. Coming from Dallas/FortWorth, my JK doesn't see any long hills. I have a 2010 Rubi 4door, lots of armor/mods, Auto Trans (with a tranny cooler), 5.13 gears and 37's... a heavy machine for the ol' 3.8 with 95k on it. It runs great and has never given me any trouble, but this will be the first time in the mountains, even if it's just on pavement I-70. I just did a coolant flush and tune-up last weekend. I have been curious if overheating or transmission heat will be a issue on the freeway west of Denver? Any other preventative measures I can do or strategies on the road to be prepared? Thanks in advance.