Strange cooling problem

I searched around but couldn't find anyone with the same issue, so let's see what you folks think. My rig is a 95 with a new water pump, new radiator (2-core), HD ZJ fan clutch, new hoses, coolant, and t-stat.

Went wheeling this weekend and driving in 100+ degree temps in stop-and go traffic, it stayed pegged at 195 for 1.5 hours. I was pleased. Then, I had to climb a mountain to get to our wheeling spot, and slowly but surely the temp increased as I climbed the hill. it was probably pushing 240 before I turned the heater on and brought the temp down almost instantly.

I wheeled all day Saturday in 85-90 degree weather crawling in 4-low (max 20mph) and the worst the temp would get is 215 before the aux fan would kick in and bring it back down to 195. I figured the climb earlier was a fluke. That was until we left and there was a grade on the highway to leave. Going about 55mph uphill, the temp crept back up again until I turned the heater on.

On the way home today again driving in stop-and-go traffic for 2 hours in 105 degree heat with the A/C on, the temp was pegged at 195 and wouldn't budge. Seems to me, it should be getting hot sitting in traffic and wheeling slowly but it doesn't. The only time it gets hot is when climbing a grade at a decent clip. The temp would keep increasing well into the red if I didn't turn the heater on. Any ideas why?

Transmission slipping? The fluid runs through a cooler in the radiator and could heat the engine up.

Nope. Should have mentioned, it has an external trans cooler.

PetrolHead said:

Nope. Should have mentioned, it has an external trans cooler.

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You bypassed the radiator completely?

Can we also assume the fluid has been replaced recently?

I would lean towards transmission problems as well....

Is the cooler in front of the radiator?

Cooler was put in by the po, I'll have to check to see if the radiator was completely bypassed. The fluid was changed when the cooler was put in about 6 months ago and looks perfect without any burny smell.

Transmission problems do seem likely, especially since it's been acting up at cruising. Just recently, it started doing this thing where when the torque converter locks, the RPMs drop WAY down. If I force it to downshift by accelerating, the next time it locks, the RPM's are normal. I also had problems keeping the transmission in the gear I wanted when climbing. When I selected 3 or 2-1 from Drive, 3 was basically drive (no change) and 2-1 was like 3. I just figured the shifter was off alignment or something. It doesn't slip at all though, it just can't figure out what gear it wants to be in. Auto transmissions are kinda like black magic to me, this is the first auto I've ever had. I prefer a clutch for these reasons.

Darky said:

Is the cooler in front of the radiator?

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Yes.

It could still be passing extra heat over. Or maybe when it's under load (climbing hill) perhaps the lower radiator hose is collapsing?

I suppose it is possible it's passing over extra heat. The tranny cooler is mounted right in front of the main fan, I guess when it could be sucking in extra heat? Still, seems strange that the transmission is getting so hot. I wonder if I'm facing some transmission problems?

I know it's a lot of work for what may be little return, but perhaps installing a temp gauge in the trans...

Well, that's what I'm going to do. The bigger question is, what could be wrong with my transmission? Why would it be getting so hot in the first place. I'm on 31's and stock 3.55 gears but still, I wonder why it's acting up?

My Jeep has the same problems climbing up steep grades. I have replaced every cooling system part. I installed a B&M trans cooler bypassing the radiator and installed a tranny temp gauge and it still overheats. If you figure out what the problem is please let me know. I have basically given up at this point and decided I would drive it until it blows then replace the motor.

You might look into adjusting the TV cable, could be off messing up the shifting on grades making the trans work harder.

http://www.naxja.org/forum/showthread.php?t=1015963

scubamark13 said:

My Jeep has the same problems climbing up steep grades. I have replaced every cooling system part. I installed a B&M trans cooler bypassing the radiator and installed a tranny temp gauge and it still overheats. If you figure out what the problem is please let me know. I have basically given up at this point and decided I would drive it until it blows then replace the motor.

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Oh goodie. Sounds like I'm in for a lot of fun and/or blowing up engines.

I was encouraged that I looked at my trans cooler this morning and found it running trans>radiator>cooler>trans which would explain the high radiator temp, but no burnt fluid or slipping trans. I'm going to swap the lines so it meets the radiator last, at least then cooler trans fluid is hitting the radiator. Now, I'm not so sure it'll help anything, but it can't hurt? Haha.

whitexj98 said:

You might look into adjusting the kick down cable, could be off messing up the shifting on hills making the trans work harder.

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Seems possible. The trans has been shifting weird, but the biggest thing is that it's ignoring the shifter (like when I'm in 3, it's basically Drive, and 1-2 is 3). Time to adjust the kick down. Any other things that could be causing it to shift funny? I hate automatic transmissions.

pop the trans down from "D" to "3" when climbing any steep grade. your trans will last much much longer without the converter slipping like crazy. don't be afraid to climb a long grade in "3" at 2500-3000 RPMs, it's not going to hurt the motor any.

GrimmJeeper said:

pop the trans down from "D" to "3" when climbing any steep grade. your trans will last much much longer without the converter slipping like crazy. don't be afraid to climb a long grade in "3" at 2500-3000 RPMs, it's not going to hurt the motor any.

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Oh, agreed! I dropped it down to 3, but it didn't respond. When I went to 1-2, it finally dropped to 3 (2500-3000 RPMS), but the heat was still climbing. I'm dreading what's wrong with the thing, it's fine in all cases when I'm not climbing.

you have some other issue then, it should immediately come out of overdrive when you drop it down to 3.

Yea, but why on earth won't it come out of overdrive?

Ok, adjusted the TV cable (didn't seem to do anything), drove the Jeep around last night and played with the shifter. Turns out when I drop it in 3, it does shift, though barely...like it'll raise 300 RPM's or so. Is this right? At 60 in 3 I'm turning maybe 2,200 RPM, which was about what I was experiencing on the grades in the mountains with high temps. Shifting to 2 would be too much at 60 (at least I think) so I either have something wrong or I need to regear. Is it possible my 31's with stock 3.55 gears are causing the transmission to work too hard when climbing, and with the cooler setup trans>radiator>cooler>trans it's raising the engine temps but everything is fine? I double checked my trans fluid last night and it's bright red without a single tinge of burned smell, so there isn't much indication that the trans is overheating.

I don't really want to remove the radiator from the trans cooler loop because we go up to the mountains quite a bit in the winter, so it'll have to deal with freezing temps on quite a few weekends in the year.