vehicles with trans temp readout

[rexlion]

On Saturday I test drove a 2013 Jeep Grand Cherokee. I was pleased when the salesman showed me that the dash display could show transmission temperature as well as each tire's pressure. After seeing my trans temp warning light come on several times on my recent trip to & from Yosemite, I could really appreciate how nice the actual temp readout would be to have.

My question: what other tow vehicles (particularly SUVs) are you aware of that incorporate this feature? Any Ford/Chevy/other products? Or is it just on Chrysler stuff?

I realize that a Scangauge or Ultragauge could give this reading, but I'm wondering what vehicles are now able to show the info all on their own. (I tried an Ultragauge... it got stolen... but before that, it was annoying because it could not be left in place above the dash in summer sun, it would overheat. Plus, the unit would not read tranny temp at all on my Toyota.)

[Hybridhunter]

tluxon wrote:
Hey BurbMan, I know you know your stuff about Burb's, so I'll take your word for it. I think you might be onto something regarding a rolling average, because that would definitely appear like a "lag" in comparison to "instant" temps. Instant temps are not always the most accurate because the reading can be reporting sensor 'spikes'. I also wonder if some analog gauges have their needles zeroed in better than others.

Thanks for the clarification on the sensor location.

15 litres of trans fluid will not overheat in a flash, it takes quite a while to raise it by 30 degrees. I can vouch for the F150 gauge moving. 230F got mine to move up 1 notch, 240F another. I'm guessing 250F is in the yellow. 1st gear WOT up the side of a mountain GCWR maxed.

[rightyouareken]

Fwiw some vehicles have multiple sensors. My 2011 Tacoma had two trans temp sensors, one in the pan and one at the outlet of the torque converter. Monitoring with a scan gauge, you could tell which was which because the torque converter sensor would fluctuate wildly depending on conditions.

[Tystevens]

Marsland wrote:
There are trans temp charts on the internet that indicate your danger zones regarding lifetime of fluid.

I've seen this chart. It appears to be made by some transmission rebuilder, not any of the engineers or manufacturers of transmissions. I'm inclined to trust the info in my owners manual, which indicates that I don't need to worry unless I'm at or over 255*.

Days are gone where 200* was considered to be a dangerously high transmission temp.

[Tystevens]

Like someone said, there is only one stock trans temp sensor. It isn't like the dash gauge connects to one sensor, and the OBDII port connects to another. Same one.

I, for one, trust that the mfgr installed the sensor in the location that is optimal for reading transmission temps, and calibrated the vehicle warning system according to temps that would be found at that location. As such, I do not know or do not care where the sensor was placed by GM. People a lot smarter than me know that readings of 255* at that location indicate a problem, and I'm willing to take that advice over someone who was working on 3-spd units under a shade tree back in 1975 (no offense intended to anyone on this board, but these new 6 spd units are different animals).

Re: different readouts, it would have to be due to the gauges. In my '06, it had an analog needle gauge that was quite small. So obviously it would have been hard to know if it was showing 197* or 203* or whatever. In my '10, the readout is digital, so obviously easier to read and get specific numbers. I would be curious to know if the scangauge gives different numbers than the digital dash readout.

[Marsland]

I've always understood that the location of the sensor makes a big difference in the data received. Is the sensor on the outlet of the trans to the cooler or in the pan? Not sure on my F150 but the readings are very stable without wide swings. On my '01 F150 I had a greater variance. There are trans temp charts on the internet that indicate your danger zones regarding lifetime of fluid.

[BurbMan]

Tim the other possibility is that temps need to be sustained for x seconds or minutes before the PCM moves the dash gauge to be sure it's not a spike, this would keep the gauge from bouncing all over the place. Next time you're towing see if you can make out any correlation between dash and scan gauges, would be interested to see what the relationship is. Is there ever a time when the scan gauge and dash gauge read the same?

I have an OBD diagnostic tool that communicates via Bluetooth and is run by an app on my phone. It also has a realtime dashboard function, and after scrolling through hundreds of variables including minutia on O2 sensor voltages, there is no trans temp option!

[rightyouareken]

One thing to note is that mfrs seem to be regulating the trans temp higher than in the past. My F150 runs 190-197 when driving normally unloaded as told by my digital readout. When towing I see 195-205 whether on flats or hills. Maybe it's for efficiency? The needle never moves except during warm up.

[tluxon]

Hey BurbMan, I know you know your stuff about Burb's, so I'll take your word for it. I think you might be onto something regarding a rolling average, because that would definitely appear like a "lag" in comparison to "instant" temps. Instant temps are not always the most accurate because the reading can be reporting sensor 'spikes'. I also wonder if some analog gauges have their needles zeroed in better than others.

Thanks for the clarification on the sensor location.

[BurbMan]

There's only one sensor for trans temp...and only one PCM that it reports to. Unless you installed a new trans temp sensor with the scan gauge. The scan gauge and dash gauge get the data from the same PCM, so not sure why the scan gauge would read higher than the dash gauge. Clearly the dash gauge works so I wouldn't automatically assume that the scan gauge is correct and the dash gauge isn't.

It's possible that the scan gauge is reading instant real time temps and the PCM sends rolling average data to the dash gauge. That's how the fuel gauge works....two fuel tanks with two sending units, and the PCM averages the readings and tells the gas gauge how much fuel to indicate is left.

[tluxon]

rexlion wrote:
...
The Jeep GC showed 170 degrees on the digital readout, just test driving around town. But you think that the on-board readout will not be accurate? I wonder how and why the mfrs would set it up to take measurements that are not accurate?
...
Question: has anyone ever compared their on-board tranny temp readout to a Scangauge or similar, to quantify how accurate or inaccurate the onboard readout was?

I don't know how accurate or responsive the readouts are on other vehicles as I only have experience with my 2002 Burb. With the Burb, there is a very real difference between the instrument panel gauge (analog) and the ScanGauge (digital). Based on the temperatures being reported, I'm guessing that the analog gauge is not as well calibrated as it could be, and there appears to be a lag between the digital temperature and the analog (needle) temperature. Sensor location may be different for the analog dash panel gauge than it is for the OBD II port's output, which would be an additional factor to consider.

Bottom line, though, is that any readout at all is going to be helpful and more useful than relying only on a warning/indicator light.

[rexlion]

Thanks for the good info. Looks like plenty of different tugs have it. Wish my Highlander had more than a light. I agree, I don't want to see that light at all.

The Jeep GC showed 170 degrees on the digital readout, just test driving around town. But you think that the on-board readout will not be accurate? I wonder how and why the mfrs would set it up to take measurements that are not accurate?

I took the HL in to the dealer (Fowler) and explained that I never used to have the light come on when towing, but on my July trip it came on several times. I asked them to look for reasons why it has changed. But I think the service advisor does not communicate things accurately to the mechanics, because the notes on my bill say,"No problems found. Light came on for safety of the trans. Getting too hot." Which tells me exactly squat. Duh, of course it's too hot! The question is WHY? Yet "no problems found." I think I have found one problem, though... the problem is the people at that dealership, I need to go to a different garage.

Question: has anyone ever compared their on-board tranny temp readout to a Scangauge or similar, to quantify how accurate or inaccurate the onboard readout was?

[tluxon]

BurbMan wrote:

tluxon wrote:
On a long hard climb it's not uncommon to see the tranny temp get up to 220°F for short periods. Since that's about as high as I want to see it, it's extremely helpful to see just how long it's up there and how quickly it comes back down.

WOW 220? I have never seen over 200-205 pulling a hill in 2nd gear!...

What gauge are you going by? It is rare for me to see the dashboard trans temp gauge read over 205, but the ScanGauge is getting the digital temperature from the OBDII port and is far more responsive and accurate.

[Tystevens]

wintersun wrote:
The GM trucks all do this but it is less helpful than you might expect. My trans fluid reads about 60 degrees hotter than the ambient air temp. If it is 60 degrees outside the fluid will run at 110-120 degrees. When it was 113 on a trip last month the fluid temp go up to 178 degrees. I am not going to drive it any differently regardless and the same applies to the tire temps. When cold the front will be at 65 and rear at 80 PSI. When they are hot they pressure goes up 8-10 PSI but so what?

What truck to you have? I have found that the trans temps in my last 2 GMs ('06 Duramax/Allison and '10 1500 Suburban) level out somewhat regardless of conditions or temps -- they don't seem tied to ambient like others always mention. Driving unloaded, it seems that temps will be between 140 and 160* once everything is warmed up, regardless of ambient temp. For example, I drove for 12 hours on the interstate in temps between -15* and +5* last winter, and my trans temps stayed in the range of 145-155* the whole trip; I drove 8 hrs on the interstate in ambient temps around 105* this summer, and my trans temps hovered between 160 and 170*.

Towing, I seem to level out around 200* all the time on flat ground, again whether it is 50* or 100* outside. Stop and go traffic will push temps up to 210*, and hills will make it top out around 225*, but it comes right back down to 200* when the hill is done.

[Tystevens]

It is good information. As noted, our '10 Suburban has it. That is the readout I have up on the display most of the time when towing.

Re: temps, IMO, there is a lot of "old" information out there about temps, effect on fluid, etc. Towing, our temps sit right around 200* all the time, and climb to 220* or so in the mountains. Per GM, there is no issue with trans fluid temp until you get to 255*, so I don't even worry about it.

But if a light is coming on, you are getting stuff too hot.