Transmission Temps: Observations and Revelation

[Ti-Ben]

Just got back from a 230 miles trip with the 25 feet TT and my 2008 V8 Limited 4x4. Wife and two young kids, total setup weighs around 11k pounds.

On our way there, 25mph front wind, a lot of med grade hills, 90F outside:

Highest trans temp 205F
Average trans temp 175F

Highest coolant temp 205F
Average trans temp 195F

Average MPG 7,5 $$$$

On our way back 15-20 mph back wind, a lot of med grade hills, 60F outside:

Highest trans temp 180F
Average trans temp 165F

Highest coolant temp 195F
Average trans temp 190F

Average MPG 11,5, I felt like I had nothing behind me.

God I love the SG II. I'm happy I read on this forum about the torque converter being locked or not, I can easily see/feel it and can adjust my driving to make it happen.

I'm very impressed how this truck handles with such a big trailer behind it! I feel very confident and solid on the road. Some people said they sold their t4r to buy a pickup truck to tow a 20 foot trailer, it made me nervous until I drove it. Now I don't understand why these people changed!

 

[OrdnanceMarine]

On our way there, 25mph front wind, a lot of med grade hills, 90F outside:..................

I'm very impressed how this truck handles with such a big trailer behind it! I feel very confident and solid on the road. Some people said they sold their t4r to buy a pickup truck to tow a 20 foot trailer, it made me nervous until I drove it. Now I don't understand why these people changed!

Do you guys even have "medium" grades out there? My subjective rating for highway speed grades would be as follows:

-Light grade: can be maintined in 4th gear with the TC locked up and 55 MPH
-Medium grade: needs at least to dip in to 3rd gear on occasion to keep 55 MPH
-Steep grade: cannot maintain 55 MPH without either seeing trans temps rising above "comfortable" (say 220F) or dropping below 55 MPH.

Obviously each of these still have subjective elements, the largest being what our payload is.

I'm also guessing you're using a weight distributing hitch, right? Using one makes all of the difference.

Looking at your MPG I can't imagine it "feels" like there's nothing back there! You must not be spending any time in 5th gear to get those numbers and must be seeing a good bit of 3rd.

 

[Ti-Ben]

On my way there with the front wind I definitly knew it was there. 7 mpg proves it badly.

On my way back, I think 11,5 mpg is not that bad considering the size and weight of the TT. Some guys with huge tires, lift, front bumper and roof rack get this kind of mileage. You can't beat physics, ask anyone pulling this kind of trailer, they all get the same numbers (unless you have a diesel). I never put it on D when towing, keep it in 4th and cruise at 60-65 mph. Engine load was 75-80%. This combined with the stability is the reason I felt like there was "nothing" behind me. Maybe some take it on the first level, it's obviously a figure of speach.

The truck didn't feel unsafe and I was very calm behind the wheel.

Probably the rear airbags and equalizer hitch helped a lot to stabilize everything.

 

[OrdnanceMarine]

On my way there with the front wind I definitly knew it was there. 7 m

If you didn't know it was there I bet your wallet did!

 

[Ti-Ben]

Do you guys even have "medium" grades out there? My subjective rating for highway speed grades would be as follows:

-Light grade: can be maintined in 4th gear with the TC locked up and 55 MPH
-Medium grade: needs at least to dip in to 3rd gear on occasion to keep 55 MPH
-Steep grade: cannot maintain 55 MPH without either seeing trans temps rising above "comfortable" (say 220F) or dropping below 55 MPH.

Obviously each of these still have subjective elements, the largest being what our payload is.

I'm also guessing you're using a weight distributing hitch, right? Using one makes all of the difference.

Looking at your MPG I can't imagine it "feels" like there's nothing back there! You must not be spending any time in 5th gear to get those numbers and must be seeing a good bit of 3rd.

Then I'd say a mix of light and medium grades. On 4-5 occasions I needed to downshift in 2nd gear and floor it, those were steep grades!

I went on a public scale, so the numbers I posted are pretty accurate.

I have an upgraded fluid cooler and drive it carefully, taking a little more speed before a hill and slowing down while climbing it when possible. Those are the reasons why the temp stays low.

 

[OrdnanceMarine]

Then I'd say a mix of light and medium grades. On 4-5 occasions I needed to downshift in 2nd gear and floor it, those were steep grades!

I went on a public scale, so the numbers I posted are pretty accurate.

I have an upgraded fluid cooler and drive it carefully, taking a little more speed before a hill and slowing down while climbing it when possible. Those are the reasons why the temp stays low.

You sound like a guy who keeps pretty good tabs about what's going on. That and you have excellent taste in brake controllers!

 

[Flexus]

Make sure not to zip tie the cooler to the radiator or condenser. The fins and passages aren't designed to carry weight. Off road the vibration may cause you to spring a leak.

 

[brockeverly]

Make sure not to zip tie the cooler to the radiator or condenser. The fins and passages aren't designed to carry weight. Off road the vibration may cause you to spring a leak.

Mine has been there for a few months (maybe 6, I forget) and I wheel all the time, no issues. I thought about that when installing it and was quickly told by someone older and smarter than myself that it would not happen and he has been using them for years.

A little more, I initially put the cooler on upside down :nono: and had to remove and reinstall it. The zipties used are next to impossible to come off. I had to drill through the center of the plastic which eventually started spinning. Without any other choice I had to spin it until it broke and I have no leaks. That is far more extreme than any vibrations you will get offroading. There is always a chance, but its quite small.

 

[brockeverly]

I just returned from a 1500 mile round trip pulling a 3000# lifted tent trailer through the Rocky Mountains. I saw temps of up to 235 degrees for small periods of time on steep (2nd gear balls out) grades, but maintained at or below 205 for the majority of the trip. I am sure that I would not want to know what the TFT would have been without the cooler.

 

[OrdnanceMarine]

Towed my trailer up to 9500' to camp at 8800' last week and saw 220F at the top of Sherwin Grade. I needed 3rd gear to hold 45 MPH during the steep climbs but much of the rest of the trip I was in 4th and 5th and kept it at 55 MPH. I saw a HUGE improvement in transmission temps! It was obvious the cooler was working by the fact that temp rises were never as fast or as high when the TC was unlocked and the moment the TC locked up in either 4th or 5th the temp dropped very quickly back to nominal. I did a lot of wheelin' during the week in 4LO and hit some good trails that were well over 9000' and again, temps didn't rise nearly as quickly and rarely was I seeing 200F. Very happy!

When I was towing I gave up using the cruise control for anything besides flat to slightly downhill since the logic the T4R uses has a tendency to allow some speed to bleed of and then has to add throttle and unlock the TC to get back to your setpoint as well as unlocking the TC at a lower LOD than driving it manually allows for. I found that under cruise control the TC would rarely lock up in 4th gear which meant my trans temp would continue to rise but when I manually manipulated the throttle I could back off for a moment so the TC would lock up and then increase the LOD to just below the point where the TC would unlock and ride the point of optimal efficiency while keeping my trans temps as low as possible.

Now I feel like I've got a setup that will keep me in this transmission for as long as possible considering the fact that I will be towing perhaps 3-5k miles per year and wheelin' a good dozen or so times per year as well. I'll also have a baseline for how the fluid is aging since I took a sample for analysis of the OEM fluid which only included one trip of hard towing. I'm expecting to change the ATF every 25k miles or so which will probably work out to 2-3 years of average driving.

 

[dsfra]

I'm hearing from the service manager at my local Toyota dealer that the ATF high temperature warning light comes on at 302 degrees F. From what I'm seeing elsewhere on the web, at that point Elvis has already left the building. These guys have an interesting graph of ATF temp vs. transmission longevity: Transmission temperature/failure chart.. Granted that they're in the business and may have their own agenda, but still food for thought - I'm just reporting what I'm seeing.

I got my ScanGauge installed and tweaked to display ATF temperature last week, and the temp tends to be ~ 150 - 170 around town in mild temps, hitting 172 at the top of a steep, fairly long hill (assuming the ScanGauge is accurate). Still haven't had it on the freeway or NW mountain passes towing 2,200 lbs on a hot day, but it sure seems like 300 would be way too hot in any case.

Still trying to confirm with my Toyota source (seems like I need one of those magic Toyota please-answer-some-basic-questions decoder rings) whether the sensor is reading the temp (1) as the ATF leaves the trans on the way to the cooler, or (2) as the ATF leaves the cooler on the way back to the trans, or (3) in the pan. The FSM (at least for 2010) pretty clearly shows that it's not the pan, as suggested in previous postings. The service manager is saying that the sensor "is on the transmission, just in front of the oil cooler inlet pipeline", which I take to mean that it's upstream of the cooler (I'm assuming that his "oil cooler inlet pipeline" = transmission outlet pipeline), but I'm waiting for clarification. The physical location/position of the sensor on the transmission isn't really the question. I'm guessing that whether it's upstream or downstream of the cooler would make a pretty big difference, else the cooler ain't doing much good.

 

[OrdnanceMarine]

I'm hearing from the service manager at my local Toyota dealer that the ATF high temperature warning light comes on at 302 degrees F. .............but I'm waiting for clarification. I'm guessing that whether it's upstream or downstream of the cooler would make a pretty big difference, else the cooler ain't doing much good.

If the light does indeed turn on at 302F then you're right, you're transmission has already taken a lickin' and you had better stop whatever you're trying to do and then change your fluid with a full flush when you finish your trip because that fluid won't be worth much at that point.

From what I could gather looking at the 2007 FSM the sensor that is being read by your SG2 is indeed at/near the port where hot fluid exits your transmission, headed for the cooler(s). 1000 miles of mountain towing while observing TFT on my SG2 seems to confirm the gauge is reading the fluid as it exits the transmission since the temps rises immediately when the torque converter unlocks and begins dropping the moment the torque converter locks back up. A pan temp sensor wouldn't behave this way.

The cooler makes a HUGE difference. I climbed some serious grades getting my trailer to 8800' with my new cooler and peaked at 220 vs the 240's I experienced on a grade 1/3 the size the month earlier. Weather was warmer and altitude was higher when I tackled the bigger grades as well, both hits to performance. Temps just don't rise nearly as quickly (once your transmission gets to full operating temp ~180F) and fall much more quickly once you crest the grade with the cooler installed.

I HIGHLY recommend adding a external cooler on the V6 if you tow in situations where the torque converter is unlocked for more than a few minutes at a time or even if you off-road in the mountains as well. The heavier the trailer, the steeper and longer the grade and the higher the outside temp, the stronger my recommendation becomes.

I'm going to be towing my rig up to close to 9000' again and we are within a few degrees of record temps in the Mojave Desert this week so it will be another good test of my transmission cooler and a good opportunity to learn more about how the systems work.

 

[dsfra]

OK - here's my dumb question for the day...

I know what a torque converter is, and I know what torque converter lock-up is, but how can I tell when it's locked or unlocked? Watch the tach and if the road speed remains constant and the rpm's go down but it hasn't upshifted then it must have just locked - and vice versa?

We're planning on lots of trips to Utah, Arizona, New Mexico, and Colorado including both on and off pavement, as well as off-road, somewhat heavily loaded and towing our Chalet A-frame trailer in the heat, and want to have a good idea about how to be kind to the transmission so we don't end up with a cooked tranny in beautiful downtown Cisco, Utah.

 

[TechWrench]

OK - here's my dumb question for the day...

I know what a torque converter is, and I know what torque converter lock-up is, but how can I tell when it's locked or unlocked? Watch the tach and if the road speed remains constant and the rpm's go down but it hasn't upshifted then it must have just locked - and vice versa?

We're planning on lots of trips to Utah, Arizona, New Mexico, and Colorado including both on and off pavement, as well as off-road, somewhat heavily loaded and towing our Chalet A-frame trailer in the heat, and want to have a good idea about how to be kind to the transmission so we don't end up with a cooked tranny in beautiful downtown Cisco, Utah.

That is about it. When the converter locks up, you will see about a 200-300 drop in tach rpm's. There is no other visual indication. Sometimes, you might be able to feel lock up when it happens, but this is not always the case.

 

[dsfra]

Thanks for the info - that's sort of what I figured. The digital tach on the ScanGauge will be good for seeing small decreases/increases in rpm, as opposed to the standard analog tach.

I got clarification about the point at which the temp sensor is reading the temp. According to the SM at my local dealer, it's "reading levels of sensor #2 – just before the fluid returns to the transmission", so that would mean it's as the ATF exits the cooler. So it must be cookin' hot as it leaves the transmission if they trigger the warning light at 302 degrees F on the cool side of the cooler. Ouch... This doesn't sound too likely on the face of it.

In any case, it sounds like it's time to go shopping for an aux cooler, even it it means flirting with a warranty debacle. Anyone have any idea about what sort of pressure is involved in the lines going to/from the cooler? The racing experience from my mis-spent youth would suggest Aeroquip lines, but I suspect that would be overkill for this.

 

[TechWrench]

Thanks for the info - that's sort of what I figured. The digital tach on the ScanGauge will be good for seeing small decreases/increases in rpm, as opposed to the standard analog tach.

I got clarification about the point at which the temp sensor is reading the temp. According to the SM at my local dealer, it's "reading levels of sensor #2 – just before the fluid returns to the transmission", so that would mean it's as the ATF exits the cooler. So it must be cookin' hot as it leaves the transmission if they trigger the warning light at 302 degrees F on the cool side of the cooler. Ouch... This doesn't sound too likely on the face of it.

In any case, it sounds like it's time to go shopping for an aux cooler, even it it means flirting with a warranty debacle. Anyone have any idea about what sort of pressure is involved in the lines going to/from the cooler? The racing experience from my mis-spent youth would suggest Aeroquip lines, but I suspect that would be overkill for this.

I can't find specific line pressure specs for the cooling line output at this time, but from past experience with auto trans, I would be very surprised if it is more that 25 psi. This circuit isn't used for anything other than pumping the fluid to the radiator cooler and back to the trans. There is no need for very high pressures. Standard, reinforced fuel line should be sufficient for this use. That is what I used. Just be careful of the ID size of the line. I can't remember the exact size I used, but I seem to recall it is an oddball one. And be careful of how you route the lines, so as not to kink them, or allow them to chafe and wear through. If you haven't already found them, there are several good threads on where to mount the cooler.

As for your SM's thoughts on where the temp reading is being taken, I am not so sure. I can't be certain on the newer model units, but I am sure on my '03 A340, that the sensor is reading the output line from the trans to the cooler. It makes sense to me, if you are going to have only one sensor, to monitor the fluid at the point where it is going to be the hottest. He might be right, but it doesn't seem to make sense to me.

Maybe someone who has actually looked at the trans, might be able to shed more info on this.

 

[OrdnanceMarine]

Thanks for the info - that's sort of what I figured. The digital tach on the ScanGauge will be good for seeing small decreases/increases in rpm, as opposed to the standard analog tach.

I got clarification about the point at which the temp sensor is reading the temp. According to the SM at my local dealer, it's "reading levels of sensor #2 – just before the fluid returns to the transmission", so that would mean it's as the ATF exits the cooler. So it must be cookin' hot as it leaves the transmission if they trigger the warning light at 302 degrees F on the cool side of the cooler. Ouch... This doesn't sound too likely on the face of it.

In any case, it sounds like it's time to go shopping for an aux cooler, even it it means flirting with a warranty debacle. Anyone have any idea about what sort of pressure is involved in the lines going to/from the cooler? The racing experience from my mis-spent youth would suggest Aeroquip lines, but I suspect that would be overkill for this.

I'll verify which where the temp report is coming from this weekend but when I was shooting the system with in infrared gun last week with the temp reading 240F I am almost positive the temp reported was close to the reading my IR gun was showing when shooting the hot fluid coming from the trans in to the primary radiator oil cooler, then coming out about 220 and going through the secondary external oil cooler and coming out around 200. I'll take notes next time to try to make sure I get the right answer.

Of interest, my folks are going to visit this weekend and we're going to drive up to Horseshoe Meadows which is a serious climb from about 3800' to 10,000' in 19 miles with most of the climb taking place in under 10 miles. They own a 2008 V6 Limited 4x4 while I own a 2007 V6 SR5 4x4. I have an aftermarket transmission cooler, they do not. I have a second ScanGaugeII and I'd like to hook it up and compare readings during the climb. This would be as close to an apples-to-apples comparison as I know how to get.

 

[dsfra]

I'll verify which where the temp report is coming from this weekend but when I was shooting the system with in infrared gun last week with the temp reading 240F I am almost positive the temp reported was close to the reading my IR gun was showing when shooting the hot fluid coming from the trans in to the primary radiator oil cooler, then coming out about 220 and going through the secondary external oil cooler and coming out around 200. I'll take notes next time to try to make sure I get the right answer.

Of interest, my folks are going to visit this weekend and we're going to drive up to Horseshoe Meadows which is a serious climb from about 3800' to 10,000' in 19 miles with most of the climb taking place in under 10 miles. They own a 2008 V6 Limited 4x4 while I own a 2007 V6 SR5 4x4. I have an aftermarket transmission cooler, they do not. I have a second ScanGaugeII and I'd like to hook it up and compare readings during the climb. This would be as close to an apples-to-apples comparison as I know how to get.

Thank you for pursuing this. I'm looking forward to finding out the results of your comparison test this weekend.

So far, I have only towed on one trip with our new F'runner, over the passes on Highway 20 in the North Cascades in Washington State. I don't believe that the ATF got too hot, since it was cloudy and rainy - in the 50's or 60's. My concern is that we're planning to do a lot of towing in high temperatures in the future, and since at this point we have "known good" ATF, i.e. it's never been overheated, I want to do whatever I can now to avoid any high temperatures that would compromise the ATF.

Has anyone played around with using the factory "Temperature Check Mode" (used to verify that the ATF is between 115 and 130 degrees when checking the level) to validate the ScanGauge's reported temperature?

Have a good trip this weekend - wish we were going too.

 

[OrdnanceMarine]

My plan was to run two nearly identical 4Runners, one with an aftermarket cooler (mine) and one without (my Dad's) with a ScanGaugeII attached to both to see what difference in transmission temps there was. Unfortunately I couldn't locate my second ScanGaugeII so the comparison didn't happen. I'll post it up if the chance comes up in the future.

 

[dsfra]

My plan was to run two nearly identical 4Runners, one with an aftermarket cooler (mine) and one without (my Dad's) with a ScanGaugeII attached to both to see what difference in transmission temps there was. Unfortunately I couldn't locate my second ScanGaugeII so the comparison didn't happen. I'll post it up if the chance comes up in the future.

Glad you made it back to civilization - thought that maybe you decided to relocate to Horseshoe Meadows permanently. Too bad you couldn't compare the ATF temps in both 4Runners, but thanks for trying.

I have since hounded my local dealer's SM, and suggested to him that his statement that the ATF high temp warning light triggering at 302 degrees sounded too high. He got somewhat indignant that I was "second-guessing" him, and then later said he heard from a regional Toyota tech resource that it's really 230 degrees, not 302 degrees. That sure sounds more reasonable. Don't know if it was a dyslexia issue, or if we're supposed to do a 2-out-of-3 majority rules and we're now waiting for the 3rd vote, or what. I do know that having owned ~ 15 vehicles over the past 45 years, this 4Runner "owner-experience" has been the most frustrating so far. Why is it so damn difficult to get information from Toyota?

In any case, I found this floating around out on the web:

A750f Automatic Transmission Pdf - Download Owners Manual PDF

According to this poorly written document, on the page labeled 165, there are 2 ATF temp sensors located at the top front of the valve body, but no one at Toyota seems to know anything about this.

"Fluid temperature sensor No.1 (OIL) is used for hydraulic pressure control. This sensor is used for revision of clutches and brakes pressure to keep smooth shift quality every time."

"Fluid temperature sensor No.2 (OIL2) is used for the switching of the shift timing control of ECT when the fluid temperature is high and ATF temp. warning light control."

I have no idea why there are 2 distinct sensors, or how closely their respective temperatures might agree. Nonetheless, if this information is reliable it does speak to the question of where in the ATF cooling system the temperature is being sensed, which was my original question, initially posed to Toyota almost 4 weeks ago and still waiting for an answer. As you may be aware, the http://www.ownersguidepdf.com/ web site is simply a compendium of pdf documents, with at best only sporadic attribution of authorship, so the reliability of this information is uncertain. We'll see if Toyota comes up with anything to confirm this, although up to now they have typically just shrugged their shoulders and said "don't know nothing".