Ever wonder how fast your auto tranny can overheat?

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:
http://youtu.be/PlqFwHFHyzI

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.

 

How are you reading your transmission temps? Is that through your OBD2 connection?

 

Yes, Scan Gauge II through OBD II port. But, I have also run tranny temp gauges on previous rigs with identical results.

 

Hmm... My Ultra Gauge doesnt read my transmission temp .

 

Mine won't overheat. I gotz a tranny cooler!

I installed it along with the tow hitch!

 

Mine does too. Yes, it will.

 

I appreciate this thread and that informative clip. I will say that when my oldest stepson lived 110 miles from here up in Folsom, Ca. when I'd run up this fairly steep and very long grade on I-80 I could smell that transmission slowbaking. That cooking metal aroma has happened since my truck was new and it still runs perfectly. Very odd how my instincts said "no worry" to such a dramatic burning smell. I would check the fluid afterwards-totally normal with no burnt smell which told me I was smelling the case and its surrounding components as they boiled up near it I guess.
This is obviously one tough transmission!

 

O.K., I'll bite. Would it be possible to hook up that thing to my truck? Now, I'm curious!

 

Depends on the year. I believe it will only read 99+ trucks. But, I don't see why not.

 

Well since my sig says I gotz a 2002, looks like it'll work.

I really would like to check this out. Will PM later.

 

ScanGauge offers a way to read the trans temp data from the ECU thru the OBDII port. You do have to program the unit with a special xgauge code which is available from ScanGauge.

http://www.scangauge.com/support/x-gauge/toyota-specific/

I only have personal experience with my '02 Tacoma and my friends '07 Tundra but have read this will also work with 2ng gen Tacomas.

 

xgauge code that digiratus posted works marvelously on my 2004 tacoma. been using it since march or so.

 

What is interesting is that that is not the code I am using. My notes indicate the following is what I entered in the xgauge settings:

[FONT=&quot]Trans Temp
TXD: 68 6A F1 01 B4
RXF: 04 41 05 B4 00 00
RXD: 28 08
MTH: 00 09 00 05 FF D8
[/FONT]

And is kind of confirmed by this thread:

http://forum.ih8mud.com/95-gen-toyota-trucks/335784-attn-scangaugeii-owners-auto-trans.html

 

That is trans temp. I'm monitoring mine with my new scanguage. Glad I did, because driving around town for extended trips I'm hitting 215. Gonna be doing a trans cooler install. And a couple things. I believe the scangauge will read the trans temp codes on any a340 series trans with the temp sensor. And when you say lock the trans out of o/d to decrease temp, it does the opposite for me, it increases temp. When I lock o/d up, it decreases

 

Can someone explain what he means by locking and u locking of the torque converter?
When does it happen?

 

When you are cruising down the freeway, and you feel a subtle 500 rpm increase without a downshift. That is the torque converter unlocking.

 

Why does that lead to increaed trans temps so quickly?

 

Because it allows slipping in the transmission. 99.9% of automatic transmissions do this

 

The torque converter also holds most of the heat in the trans. It holds the fluid in till it unlocks, and when it does the temp increases. But I never have the torque converter unlock like that. It licks like that and drops rpm, but it never unlocks and increases 500 rpm

 

No. It creates more heat when it unlocks. And yes, it does jump 500rpms when it unlocks.

Run on a slight incline into a headwind, and it will unlock. Tow with it, it will unlock in OD.

Next time your driving it, tap the brake with your left foot at speed for a sec. What you will feel is the torque converter unlocking. Take a look at how high your rpms jump.