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Trans running hot

My sensor is hooked up just like yours, but it's inline with the hard line (hard line on each end of the sensor) and is a one-wire sensor.

Also, I was on the interstate and not going up any hills that i was consider "big". I would like for the transmission to run cooler than 210* on the interstate.

Do you think that if I were to plumb the transmission fluid back through the radiator, then to the aux cooler, it would drop the temp significantly?
 
Personally, my opinion, there's nothing wrong with plumbing it through the radiator. I don't think it would change much. If you get cold winters (COLD around here is 30ish), then having a run through the radiator is a good thing.

For me, it's not my DD and I use it most in the summer, regularly 90-100, heat. I can't think of any way that running it through the 210 radiator "heat exchanger" can cool it at all.

My opinion.
 
mines (2001 aw4) plumbed from trans to temp sending unit (with added ground to body of sender) then plumbed to a filter adapter with a wix 51515 (to gain volume and a real filter).

then through my after market cooler (in front of ac condensor and fan pass side) then through radiator heat exchanger ..

mine usually runs at about 150 to 160.. But if I'm pushing it (or using the overdrive) it will get up to 170 (havnt seen it higher yet)..

I also replaced all fittings w 6an fittings and jegs pushlok hose.. ( not shure if that helps flow better )..

I DD and it gets hot in stl. But I went through exchanger because I get up in the mountains in co. And it sleeps in the snow and needs to run well in the morn.. Also the stock aux cooler still goes through the rad.

as an added bonus my motor allways ran right at 210 now it's slightly cooler than that at normal operating temps
 
The FSM says "normal" is 122-176. I see 150 on the interstate at 75mph, but it's basically flat here. I've never seen mine get above 210, even when pulling a loaded trailer through town. B&M stacked plate cooler, in-radiator exchanger bypassed, stock gears and ~30" tires, blah blah.

bigalpha said:
Do you think that if I were to plumb the transmission fluid back through the radiator, then to the aux cooler, it would drop the temp significantly?
Click to expand...

I've run mine with just the exchanger, the exchanger and the cooler, and just the cooler. Plumbing it through the exchanger did not lower coolant or ATF temps, which makes me think it's not particularly useful except when the ATF is very cold or very hot.

The first thing I would do, is put a meter on the fitting for the temp sender, and make sure it's properly grounded.
 
Last edited:
Okay, so I went and drove at all sorts of speeds and did the torque converter test - drive at constant speed, hit brake while driving.

I did it at different speeds (45+) with different levels of brake pressing. I never saw the 300RPM spike and didn't feel anything either.
 
ParadiseXJ said:
Personally, my opinion, there's nothing wrong with plumbing it through the radiator. I don't think it would change much. If you get cold winters (COLD around here is 30ish), then having a run through the radiator is a good thing.

For me, it's not my DD and I use it most in the summer, regularly 90-100, heat. I can't think of any way that running it through the 210 radiator "heat exchanger" can cool it at all.

My opinion.
Click to expand...

Under heavy loads, like climbing and towing it will help keep it from overheating (if it is getting past 200, to say 220-250, then it will cool it fatser, before it gets to the air cooled after cooler, thus a net gain in cooling), and in the winter warm it up faster. If the cold side of the radiator is running at 200-210 that is already a problem! Cold side of the radiator should be 180-190 peak!
 
hubs97xj said:
The FSM says "normal" is 122-176.
Click to expand...

Ecomike said:
Cold side of the radiator should be 180-190 peak!
Click to expand...

not doubting anyone's info, but one of these two doesn't make sense. The "cooler" in the radiator isn't designed to heat the trans fluid under normal operating temps.

122*-176* would almost make sense if the fluid were equal to the radiator output temp and then passed through an auxiliary cooler. Are we sure the temp listed isn't for the return line on vehicles with towing package?
 
If you're testing after the coolers, you're not going to get consistent data when there are at least three different factory configurations, so logically you'd need to test at the trans output to get meaningful numbers. At least that's my assumption.

The FSM does not specify test points, or which system is tested. I would think that, with only one book, the listed range of "normal" temps would cover all factory setups. The same Jeep with three different setups, under the exact same "normal" driving conditions (not "Severe" or "Commercial use", both of which are mentioned in the FSM and suggest it be regeared and have the upgraded water and trans cooling setups) should run at or near the same temps, wouldn't you think?

Regardless of what the book says (and doesn't), I'd check fluid level, the sensor ground path, the wiring, and I'd compare gauge temps to IR thermometer readings of the line and fitting. My opinion, is that something is obviously wrong, and I'd verify those things first.

edited to clarify a couple of statements
 
Last edited:
Shorty said:
not doubting anyone's info, but one of these two doesn't make sense. The "cooler" in the radiator isn't designed to heat the trans fluid under normal operating temps.

122*-176* would almost make sense if the fluid were equal to the radiator output temp and then passed through an auxiliary cooler. Are we sure the temp listed isn't for the return line on vehicles with towing package?
Click to expand...

Good question on the towing package.

Actually the cooler in the radiator is designed to heat Tranny fluid if the T-fluid is cold, like cold winter start ups.

Under cold ambient conditions and short trips, and cold morning start ups it heats the T-fluid, under heavy loads and long trips it is there to cool if needed, if the fluid gets over say 200 F. I think the idea is optimize the T-fluid properties by holding the operating temperature in a narrow range.

The entire transmission tends to act (when clean) like a heat sink cooler.

Keep in mind that heat moves from a warmer place to a cooler place, so the heat transfer goes both ways, depending on fluid temps on both sides. Lastly just like it is important to get the oil hot enough to evaporate off condensed water, it is equally important for the T-fluid to get hot enough to flash off condensed water.

Lastly, one might dig up the Toyota manual to look for the T-fluid temp range details.
 
Okay thanks.

I have an IR thermometer, a FLIR camera and a multimeter that I can check it all with. When driving around down, it stays at about 160* and doesn't waver.

I obviously want this sucker to run as cool as possible, so after I verify the ground on the sensor, and the accuracy of the gauge to the temp I measure at the Trans Out line (where the gauge is mounted), I'll report back. It may be a few days, though.
 
So, there was something that I overlooked.

A while back, I installed a 99 booster but didn't alter the push-rod, so the pedal was pushed real far up. There is some small switch that's mounted in front of the pedal up high. It's white - i'm not sure what it's for. Well, the pedal was pushing that switch in this whole time.

I have recently fixed the pushrod and it's all stock again.

I haven't had a chance to take it out on the interstate again to re-test, but I thought I'd just throw that out there.
 
I'm pretty sure that's the case. Google search for combinations of torque converter lock up brake switch on here, and you'll get a lot of returns. But basically, no lockup means the clutches slip more, creating more heat. I'd take it for a drive and see where your temps are at now.
 
Cruiser54 swears that the white switch is for the cruise control, to shut off the cruise when the brake is applied. It is a vacuum switch and an electrical switch. The electrical switch tells the cruise computer to turn off the cruise, and the vacuum shuts of the vacuum (bleeds?) to the actual actuator on the cruise module under the hood, that operates the throttle.

The lower, normal style brake switch has 2 pairs of wires, one pair for the brake lights, one pair for the TCU signal to tell the TCU to unlock the TC.
 
Let's not rehash the semantics argument again. That switch should normally be open, but was constantly closed. big has higher than normal temps, and a switch in the wrong state. Let's focus on his problem. We can argue about petty details later. :)
 
I will be driving my truck a few hours on the interstate on Sunday so I'll see how the temps respond.

The switch that is lower on the pedal - the one that works the brake lights - it only has two wires on it.

I also don't have cruise control.
 
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