Transmission temps, the saga continues, and more questions

OK, so I got an OBD app working to get real temps on my tranny. From what I can tell there is only a trans pan temp sensor viewable, not a torque converter sensor? At least not a TC sensor viewable by these apps like Car Scanner Pro. Can anyone verify if that is correct?

Anyway, whatever the factory tow gauge on the dash uses as a sensor must be really sensitive and sense the temps really rapidly, or be in a location within the transmission fluid plumbing where the temps fluctuate quickly. I say that because I was able to get the temps on the dash gauge to get hot and move up to at least 3/4 on the gauge as usual with a slow speed load(and what first alarmed me), yet the trans temp in the pan according to the app never got over 194 degrees. Additionally, once the slow speed load is relieved, the temp on the dash goes back to the normal mid way mark within seconds, yet the 194 degrees in the pan temp remains steady long afterwards. Why is that?

Where is the sensor on the dash gauge and why does it fluctuate so much? Must be post TC and before the cooler to read hotter and more volatile than the pan temps, right? Which temp is more important to monitor, the temp measured by the dash gauge and wherever it comes from? Or the pan temps as measured on the app? I have my own theory, but it’s just that. Would like to hear others thoughts.

And lastly, at what point do pan temps become concerning with these new fangled fluids?

 

I dont think the temperature differential between the TC and the pan should be that high. Maybe 20*. I would not expect the temp gauge to even respond to 215-220F temps.

I know the guys on the land cruiser group that monitor them while towing 7000-8000 lb trailers with the TC unlocked might see a 30* difference max when they are working the truck hard. 230 in the pan and 260 at the TC.

Are the fluid new fangled or is it still Toyota WS? I would think that temporary excursions to 240F are fine. Thats what my LX does. On really large climbs towing(when I have to pull the hill in 3rd or 4th gear) I can get pan temps around 240F but as soon as I let out at the top it comes right back down. For less difficult climbs(in 5th) and flat ground it generally runs <200F. That 2 minutes it spends at 240F is not going to make an appreciable difference in transmission fluid life.

 

Well I can tell you for certain, the dash gauge definitely can move up into the very high range with the pan temp still at 194. The dash gauge can spike even with the pan temp in the mid 190’s and then quickly settle back down to mid range once the load is relieved, all the while the pan temp stays steady. That tells me the dash gauge must be post converter.

I just wish I could get a real temp on the same location the dash gauge uses. I don’t see an option to get a post converter reading on Car Scanner.

 

There are two sensors within the transmission, but only one is visible to the OBDII port...

The one that is visible to the OBDII port is within the Valve Body...

The other one appears to be post converter and I would surmise that the dash is the post converter sensor...

I cannot be 100% on what I stated above as what I've seen isn't exactly clear nor is it described in any detail.

There are two sensors. I've 100% sure on that.

 

Thanks I guess that makes some sense. The app calls it the pan temp, but I’d assume pan temps and valve body temps should be the same or similar since that fluid has already been cooled and not exposed to much heat yet. Am I correct in that thinking?

 

I'm with you on the thought process and process of elimination...

 

Ok so then what is the threshold for acceptable pan/valve body temps (that are actually readable) when we know the post torque converter temps are much higher (but not readable in a quantified manner)?

 

Looking...

 

The Scan Gauge III in my ‘21 is plugged into and powered by the OBDII port and the gauge does read trans temp1 and teams temp2. The consistently higher of the two I imagine, is the converter temp, so there are definitely 2 sensors accessible through the port, at least for the Gen 2.5.

 

Thanks...3rd Gen is certainly different in this regard...

 

Another question…

what about running these 4x4 trails with my AC on? Would the condenser clutch fan create more air flow to cool the tranny?


And I still would like to know: 1. If the oem dash gauge can be confirmed as coming front the TC, and 2., How much hotter my TC output temps are vs the pan!

 

Yes, agreed but that’s in the pan. Why is the dash gauge nearly redlining if 194 is nothing to worry about?

 

Probably to warn the operator before it does overheat and cause damage. If it's not reducing power I see it as a warning and to change/stop what your doing. 4lo wink or even lower the tire pressure if your in soft stuff. I'm sure there is another level of warnings that will reduce power once the Temps go even further.
My pos f150 was blowing fluid out the vent tube onto two cat converters 230-240ish highway unloaded and no warning lights.
*have you tried Tow/Haul mode?

 

Yes I tried tow/haul. Helped a little. Just a little.

 

if it is under 200 you should be good. Mid 190's would not concern me.

 

Wow! If that’s the case, then I can’t for the life of me understand why the dash tow gauge red lines so fast and so much earlier. I wish someone could answer my questions in post 11. Sure would help riddle this out!

wouldn’t it be nice to have a resident Tundra engineer!

 

A faulty gauge was my initial thought, and the dealer’s too, but ultimately they ruled that out. So they said.

who are the engineers? Can we tag one to maybe get some insight?

 

I mean come on, they should give us actual numbers on everything. The little bar graph is disappointing…even my little 2016 wrx shows actual numbers for oil and coolant…I get why they do it, maybe a dealer unlocked option for people that actually tow….
Sorry for the rant haha, glad it’s not as bad as you thought

 

Probley a gauge for the refrigerator in the sleeper too. Lol

 

Does your pan temp fluctuate from the 194*? Once it's warmed up and you driving around normal, does the temp fluctuate? The 2.5 gen also has 2 sensors TC and Pan temp. Usually they are about the same when cruising. When stopped the TC temp creeps up but then settles down when you start moving. My trans temp is constantly fluctuating, it never stays at a fixed temp. If your temp doesn't fluctuate then the issue could be the PID in the app. I know there's been memebers that have had to reconfigure the values for different Obd dongles and apps. My OBD Link MX+ has been flawless from the start.

 

It changes some. Very slowly and gradually works up to 190+. Then seems to run right around 195, give or take a few degrees. The gauge on the dash definitely does seem to fluctuate A LOT more, regardless of the pan staying a fairly consistent 195 ish. Hence my questions.

That said, since getting Car Scanner I have not been back up to the ranch to really give it a workout hill climbing in 4x yet. That’s what really seems to heat things up.

 

Neither here nor there but sometimes at long lights I like to shift to neutral so I’m not sitting there stalling the converter…I hope the frequent shifting from neutral to drive isn’t worse.

 

It’ll be nice to see some data once OBD Fusion has you guys sorted out.

I’m using the 2021 Toyota pack for the Tundra and the 2009 pack for the Lexus. I drove my kids to school today in “beast mode” (lol. While it is fun to let the 3UR rev high, a sports car it is not). That’s with all nannies off and T/H engaged.

Here is my readout after 7 mi, 3 of which is a long highway grade. I took this screenshot while coasting on the exit ramp. My truck stayed locked up in 5th accelerating up that grade to 80mph ( lots of slow trucks to pass).


Thermostat still hasn’t opened up 15min later. (It opens at about 195°F).

 

Is that above for a third gen Tundra? My OBD Fusion only gives one temp readout. And they claim they don’t have anything out yet for third gen Tundras. I’ve emailed with their CS.

 

If your pan is staying in the 190's while the gauge is getting close to red then I am going to say that it may be faulty gauge programming. That was an issue on some Jeep Liberty CRD's and the dealer had to update the PCM to fix it.

 

Again, supposedly the dealer went over the dash programming. And the dash gauge is quite predictable in when it spikes. It only does it low speed hill climbing, TC unlocked. Doesn’t do it randomly just going down a flat road or highway. Seems if it was faulty, it would spike unpredictably.