Ever wonder how fast your auto tranny can overheat?

[AddictedOffroad]

I love all the "my A/T Temp light came on" threads.

So, I decided to show you just how fast an A340 auto tranny in our trucks/4runners can actually overheat.

Just an FYI, the dummy "A/T Temp" light doesn't come on until the tranny hits 300 degrees. So, when that light comes on, you've already smoked your tranny.

When the torque converter unlocks in OD, you will see pretty much a one degree per second increase in temp. This is why its so important to run a tranny temp gauge, or Scan Gauge to monitor your temps.

This video was taken today on flat ground. It was roughly 35* out and I was driving into a stiff 25-30mph wind. You'll notice when the torque converter unlocks because the rpms will jump a few hundred rpms when it happens.

Here you go:
Tacoma A340 automatic transmission temps - YouTube

Now, the best thing to do when you start hitting temps over 220* is to simply kick the tranny out of OD. When you do this, it locks the torque converter and the temps will drop just as fast as they went up.

 

[BrianSD_42]

So are you suggesting that when off road we just keep the OD off?

Assuming we are in 4WD

 

[the great him]

so your video is great, but it can be misleading... see you only did this for a short period, not long enough to get the housing hot... temps will climb exponentially the hotter it gets, a big part of that is the case or housing heating up. once you get all the internals and housing hot from the thermal convection it will will take a lot longer for the temps to cool. some people think that just pulling over and putting the vehicle in park or neutral will help cool temps. actually that wont be as effective as keeping the vehicle moving. air flow will help cool the case/housing as well as flowing over the cooler. just simply stopping will allow the ambient air around the trans to heat up and that wont help cooling. this will be even more of a problem for those of us will full belly skids,as those hold the head it and drasticly cut down the air flow, as well as hold the heat in from the catalytic converter. and obviously the bigger the tire you have or the more weight you have the faster temps will heat up too.

 

[AddictedOffroad]

So are you suggesting that when off road we just keep the OD off?

Assuming we are in 4WD

No. Honestly off road usually isn't a problem. On my old 00' 4runner crawler I never had an issue. It would run 150-160* all day wheeling.

But, I would tow my pop-up through the mountains all the time with that rig. I ran a Scan Gauge II and a dedicated gauge on it. Neither lied.

It doesn't take much to see tranny temps get up there. Towing or not. OD off button should be used with or without a load on it in the mountains. When you know the torque converter in unlocking, then you don't have long before its too hot.

 

[LittleCaesar]

Those tires can't help, that is for sure.

Nothing kills a tranny faster than heat. Tow out of O/D, except possibly while 65mph+ on flatlands and/or low hills.

I have found, through indirect experience, that by mounting a spin on tranny filter set up (B&M) right behind the passenger side headlight and before my 70264, my tranny temps have never stayed so cool (below 175 all summer while sometimes towing a 20ft boat or in DC stop and go traffic). I also run both B&M products in line with the ATF radiator exchanger, using Amsoil ATF. I want to see what the temps are during an entire winter before drawing any further conclusions.

 

[AddictedOffroad]

Those tires can't help, that is for sure.

Nothing kills a tranny faster than heat. Tow out of O/D, except possibly while 65mph+ on flatlands and/or low hills.

I have found, through indirect experience, that by mounting a spin on tranny filter set up (B&M) right behind the passenger side headlight and before my 70264, my tranny temps have never stayed so cool (below 175 all summer while sometimes towing a 20ft boat or in DC stop and go traffic). I also run both B&M products in line with the ATF radiator exchanger, using Amsoil ATF. I want to see what the temps are during an entire winter before drawing any further conclusions.

Those tires pictured were 37s and pushed by 5.29s and a supercharger. It was a rarity that the torque converter would unlock on flat ground let alone mild hills. I ran a 24,000lb gvwr cooler on that 4runner and bypassed the radiator altogether.

However, today's video was in a stock 04' Tacoma pushing 265/70r16s. The truck has 4.10s and unlocks very easily. It doesn't take much to get the torque converter to unlock in OD. With a 70% overdrive in the auto Toyota severely under geared these rigs.

The point of the video is to show people how fast the tranny temps climb when the torque converter unlocks. Also, the need for a gauge.

That being said, I don't care what cooler you run or fluid. The tranny will pick up a degree per second when unlocked. This is fact.

I am running the Lexus version of this tranny in my buggy and its no different. IMHO, it can withstand more heat than most American made trannies, but you still need to be aware of how hot its getting.

 

[NateMob]

Thanks for the info, I had no idea the transmission could build heat that quickly!

 

[AlphaEcho2k5]

Thanks for the info, I had no idea the transmission could build heat that quickly!

X2, appreciate it.

 

[UTEP]

Pretty cool!

I've always been curious as to how torque converters, overdrive and automatic transmissions actually work.

Any suggestions for a primer?

Also I understand the only time to disable OD is when pulling a steep grade; towing or not. Is this a good rule of thumb?

Gracias,

Utep

 

[BrianSD_42]

Also I understand the only time to disable OD is when pulling a steep grade; towing or not. Is this a good rule of thumb?

There is no downside to disabling OD at other times.

For example I sometimes disable it when driving around town because I don't like the extra shifting going up and down light hills.

 

[opie74]

Another point of contention, and someone correct me if I am wrong, but the transmission temp. sensor measures the fluid as its coming out of the TC.

 

[Montreal2013]

This is why its so important to run a tranny temp gauge, or Scan Gauge to monitor your temps.
.

But, I would tow my pop-up through the mountains all the time with that rig. I ran a Scan Gauge II and a dedicated gauge on it..

Does the Scangauge show transmission temps right out of the box or did you have to download extra software?

 

[afg10000]

Does the Scangauge show transmission temps right out of the box or did you have to download extra software?

You'll have to plug in a series of numbers into the xguage section of the unit. Only works on '99 or newer Runners IIRC.

 

[AddictedOffroad]

Does the Scangauge show transmission temps right out of the box or did you have to download extra software?

I input the Xgauge command for it.

 

[Montreal2013]

What kind of temps have you noticed while going up and down the mountains? Especially while driving up and down 3,000 or 4,000 ft elevation (my local drive).

 

[AddictedOffroad]

What kind of temps have you noticed while going up and down the mountains? Especially while driving up and down 3,000 or 4,000 ft elevation (my local drive).

I don't let my tranny run warmer than 215*. If its heading North of that, I kick it out of OD.