Transmission Temperature Gauge

For those who do not have a transmission oil temp gauge on their TV but would like to be able to check the Transmission temp under adverse towing conditions, here is a possible option to installing a dedicated transmission oil temperature gauge ($??).
For $300 and a LapTop Computer (or PalmPilot), you can buy a gadget to connect to your TV computer diagnostic connector. It lets you monitor 100's of TV parameters besides the transmission temp. You can have your co-pilot watch the readings or you can simply log the data to the hard disk for later viewing. Your TV must be 1996 or later offering OBD II diagnostic data. This may be less expensive than installing a dedicated temp gauge. It has a nice GEEK factor as well :-)
Mine is used on 2002 GM product but Ford and Chrysler versions are available too.

What product are you referring to?

[RockyMtnRay]

Originally Posted by hingarfi

For those who do not have a transmission oil temp gauge on their TV but would like to be able to check the Transmission temp under adverse towing conditions, here is a possible option to installing a dedicated transmission oil temperature gauge ($??).
For $300 and a LapTop Computer (or PalmPilot), you can buy a gadget to connect to your TV computer diagnostic connector. It lets you monitor 100's of TV parameters besides the transmission temp. You can have your co-pilot watch the readings or you can simply log the data to the hard disk for later viewing. Your TV must be 1996 or later offering OBD II diagnostic data. This may be less expensive than installing a dedicated temp gauge. It has a nice GEEK factor as well :-)
Mine is used on 2002 GM product but Ford and Chrysler versions are available too.

The problem with all laptop and most PDA (PocketPC or Palm) displays of engine/transmission characteristics is the safety/human factors/ergonomic considerations. If the display of transmission temperature (or any other drivetrain indicator) is not within the driver's normal eye scan (road, instrument panel) such that the road ahead is ever out of your peripheral vision, it's deleterious to safety. Period. End of Discussion. Even a half second interruption of peripheral vision of the road ahead can be fatally dangerous.

Furthermore, even if a PDA is used for such information and is placed right in the normal eyescan, there's likely still a problem. If the display font size is much smaller than the text used by the vehicle maker for instrument panel guages, then the time spent focusing on the PDA again is major distraction because it interupts the eyescan that all good drivers use. This is compounded by the fact that nearly all such displays are digital (which require some thinking) versus analog (which can provide a general idea much faster based on basic needle position (low-medium-high)).

So although a laptop or PDA display of ODBII transmission temperature data (for those vehicles that provide it) has an exceptionally high geek factor...and is a low cost way of displaying that data...it's downright dangerous from a safety viewpoint and a really poor technique from a human factors/ergonomics viewpoint.

For those who regularly do mountain towing (the only situation where transmission temperature is a worry), it's much, much smarter to install a proper analog gauge that's located right in the normal driving eyescan and which does NOT require losing direct or peripheral vision of the road ahead. In nearly all cases that means installing an A-Pillar analog gauge as I've done. See picture for my Autometer Z-series gauge...A-Pillar mounted, easily read (a near perfect match with the stock instruments), and directly within my normal eyescan pattern.

Ray:

I agree that trying to look at a laptop while driving is very dangerous. As I noted, “You can have your co-pilot watch the readings or you can simply log the data to the hard disk for later viewing.” I certainly did not imply that one drive around with the laptop sitting on the dash. You use it as a test under the most adverse towing conditions to determine if your cooling is adequate. Then you can tow at ease knowing that the transmission temp is OK. It's a one shot test. I had a 2500 Chevrolet truck with temp gauge. Once I had watched it under some heavy towing, I rarely ever looked at it again. But a temp gauge, as you have, is obviously the best solution. Most serious TV's have such a gauge. However, I suspect that many people towing TM’s do not have a transmission temp gauge and may be damaging the transmission unknowingly. My suggestion was for those who would care to check the transmission temp and have a device which has other DIY uses.

[RockyMtnRay]

Originally Posted by hingarfi

Ray:

I agree that trying to look at a laptop while driving is very dangerous. As I noted, “You can have your co-pilot watch the readings or you can simply log the data to the hard disk for later viewing.” I certainly did not imply that one drive around with the laptop sitting on the dash. You use it as a test under the most adverse towing conditions to determine if your cooling is adequate. Then you can tow at ease knowing that the transmission temp is OK. It's a one shot test. I had a 2500 Chevrolet truck with temp gauge. Once I had watched it under some heavy towing, I rarely ever looked at it again. But a temp gauge, as you have, is obviously the best solution. Most serious TV's have such a gauge. However, I suspect that many people towing TM’s do not have a transmission temp gauge and may be damaging the transmission unknowingly. My suggestion was for those who would care to check the transmission temp and have a device which has other DIY uses.

Ooops...sorry, missed that "co-pilot" part. As an Engine/DriveTrain and the Towing Moderator at TundraSolutions, I've had to deal with way too many guys who focus solely on the techie side of getting some kind of display (laptop, PDA, gauge under the dash) working without any consideration of the safety/human issues...and that tends to cause me to have a knee-jerk reaction. But, yes, you are correct, if the temperature is being monitored by the co-driver (or being recorded), then use of a laptop or PDA is reasonable and safe.

And you are probably right...a fair number of folks possibly do have insufficient transmission cooling for towing, especially those who are using minivans with their ultra compact transmissions and no external cooler.

And for those who do want to do this kind of monitoring...there are several ODBII readers that plug into laptops that are much less then $300. I have the "Car Code ODB-2" model from http://www.obd-2.com/. Costs only $122 and comes with software and the needed interface cable. I use it to monitor fuel and timing trims as well as to have immediate readout of the problem codes should I ever have a "Check Engine Light".

Although I seldomly pay much attention to my truck's tranny temp gauge in normal driving, I still monitor it pretty closely when towing, especially on all mountain grades. There are four factors that will drive my truck's transmission temperature up...steepness of grade, length of grade, road speed, and ambient temperature of the air. Some of the highest transmisison temperatures I've seen so far (around 195 degrees) were on a moderate-for-Colorado 5 to 6 percent, 6 mile long grade with ambient temperatures in the 90s. A seemingly much tougher 8 mile long, 7% grade only caused a transmission temperature of 180 degrees...but the ambient temperature was in the low 50s...and I was able to hold 60 mph so had good airflow through the cooler and radiator. And a relatively easy 4 to 5 percent grade produced 185 to 190 degrees...but the ambient temp was around 95 and the road had so many sharp curves that I could only go about 30 mph and simply wasn't getting much airflow through the cooler/radiator. (As a reference, I normally see transmission temperatures of around 150 when towing at 65 mph on level roads with the ambient temperature in 80s).

So I would somewhat disagree that once you've seen the transmission temperature under what seemed to be "heavy towing", you don't have to pay much attention to the transmission temperature thereafter. All it would take is a little longer or little steeper grade...or 10 degrees higher ambient temperature...or driving at 35 mph due to curves instead of getting good airflow at 65 mph...and the transmission temperature could easily get into a danger zone (over about 210 degrees).

Based on literally thousands of miles of mountain towing, I would argue that anyone who regularly does mountain towing needs to have a real transmission temperature gauge mounted in their eyescan area where it can (and should) be monitored on every climb.

[Bill]

Ray -

I don't disagree with anything you have said. HOWEVER, I have been unable to find anyone that I consider reputable (including two Ford dealers and at least two transmission shops) that is willing to drill a hole in the transmission pan and install the fitting for the sensor. Some of them have simply declined without explanation, some have told me that they are afraid of the liability issue if there is a tranny failure in the future.

As I recall, you had to jump through some hoops to get yours installed.

By the way, some of these guys have also pointed out that a pan-mounted sensor measures the temp of the fluid in the pan (duh!), which is only loosely related to the temp of the fluid in the torque converter. And it is the temp in the torque converter that matters. I'm not sure what to make of that. I suppose any indication is better than none, which is what I have now. But let's agree that pan temp probably WON'T tell you if the fluid is getting so hot that it is starting to degrade - because the degradation is happening in the torque converter.

So that begs the next question. Where does the OBD-II system measure temperature? I believe that it is measured somewhere in the guts of the tranny, not in the pan. I say this based on the 600-page book of Explorer wiring diagrams that I bought from Ford. It shows the sensor as mounted inside the tranny, with the shift solenoids and the torque converter lock solenoid.

Finally, there is a subtle but interesting implication to the discussion of OBD temperature readouts. The fact that there is a temperature readout means that the vehicle already has a temperature sensor. You don't actually have to buy and install one! And in my Ford, anyway, it is analog to boot! I have been thinking about tapping into the wire that leads to the sensor - it is readily accessible in a connector on the firewall - and using it to drive an analog meter. I may not be able to screw up my courage, since the consequences of messing it up could be severe. But it is interesting to know that the sensor is already there.

Bill

[fcatwo]

Bill

Ray has posted quite a bit of trans temp info in the past and I'm sure he will again. He has an incredible capacity for answering the same questions over and over without apparent frustration. In the meantime I can share my experience. I DIY'd a gauge in our previous TV, a 2002 Honda Odyssey minivan, and found it quite valuable. I haven't installed one in our Tundra however because Ray's readings from his Tundra are well below the danger point most of the time and our Tundra's torque converter stays locked up most of the time - even while towing. For instance, we towed the TM with the Tundra from San Diego to Seattle a couple of months ago with OD locked out and I don't think the Tundra downshifted or unlocked it's torque converter a single time during the trip. Although the mountains along that route are nothing like the Rockies there are several passes in the 2-4K range. The Odyssey which could not be locked out of 5th without also locking it out of 4th would have shifted or dropped out of lock up 500 times (my estimate) on the same trip.

I did see high temps in the odyssey on occasion but my gauge was reading the oil temp as it came out of the torque converter rather than after the coolers. Although professional opinions seem to vary, many feel the few seconds the oil spends at those higher temps is not a serious problem so long as they are cooled before returning to the trans pan. My experience was that if you could keep the trans locked up it wouldn't get too hot except in extreme situations like slow climbing in hot weather. One thing that surprised me was how quickly the temp rose while sitting in gear and idling at traffic lights in hot weather. Some Odyssey owners who drove regularly in those conditions reported brown trans fluid at the 15K fluid change point while mine with 14K of towing behind it was still pink at the 30K mark.

I might mention that I ordered a temp-sender "T" from a supplier and cut the trans fluid hose between the torque conver and the coolers and plugged it in. If I do it again I will put it in the hose between the coolers and the pan. All of the "not above X" trans temp charts I've seen are apparently referring to pan temps since that is where most senders are mounted.

IMO only those people who's TV torque converters are unlocked much of the time need a gauge. They are not a big deal to install however. I removed mine before trading and it's sitting on a shelf in my garage if I ever feel a need for it.

Frank

[RockyMtnRay]

Originally Posted by Bill

Ray -

I don't disagree with anything you have said. HOWEVER, I have been unable to find anyone that I consider reputable (including two Ford dealers and at least two transmission shops) that is willing to drill a hole in the transmission pan and install the fitting for the sensor. Some of them have simply declined without explanation, some have told me that they are afraid of the liability issue if there is a tranny failure in the future.

As I recall, you had to jump through some hoops to get yours installed.

By the way, some of these guys have also pointed out that a pan-mounted sensor measures the temp of the fluid in the pan (duh!), which is only loosely related to the temp of the fluid in the torque converter. And it is the temp in the torque converter that matters. I'm not sure what to make of that. I suppose any indication is better than none, which is what I have now. But let's agree that pan temp probably WON'T tell you if the fluid is getting so hot that it is starting to degrade - because the degradation is happening in the torque converter.

So that begs the next question. Where does the OBD-II system measure temperature? I believe that it is measured somewhere in the guts of the tranny, not in the pan. I say this based on the 600-page book of Explorer wiring diagrams that I bought from Ford. It shows the sensor as mounted inside the tranny, with the shift solenoids and the torque converter lock solenoid.

Finally, there is a subtle but interesting implication to the discussion of OBD temperature readouts. The fact that there is a temperature readout means that the vehicle already has a temperature sensor. You don't actually have to buy and install one! And in my Ford, anyway, it is analog to boot! I have been thinking about tapping into the wire that leads to the sensor - it is readily accessible in a connector on the firewall - and using it to drive an analog meter. I may not be able to screw up my courage, since the consequences of messing it up could be severe. But it is interesting to know that the sensor is already there.

Bill

As Frank notes, there's a lot of disagreement about where the best place is to measure transmission temperature.

Some people (like the mechanics you talked to) think the temperature of the fluid in the torque converter is what you should measure since that's where the hottest fluid is. The easiest way to measure that is to put a sensor in the line from the transmission to the cooler(s) since that line comes directly out of the TC.

Other people (me included) take note of the fact that fluid degradation is a function of both elevated temperature and time spent at the elevated temperature. Yes, the fluid in the TC is hotter than in the pan but (1) only when the TC clutch unlocks, (2) is only about 20 degrees hotter when the clutch does unlock, and (3) it stays hotter than the pan for only a matter of seconds before it goes through the cooler(s). By comparison, if the fluid in the pan is too hot, it will be too hot for a period of minutes or even hours.

Furthermore, damage to a transmission from overheated fluid is primarily to the seals (and somewhat because of warpage in the clutches/bands)...and the fluid that's going past those internal components is coming directly out of the pan so they are, in essence, immersed in pan temperature fluid. Accordingly, if you look at the footnote of this chart of transmission lifespan vs fluid temperature, you'll see it notes "transmission temperature reading taken in the pan". Other charts I've found that relate transmission fluid temperature to either fluid degradation or transmission lifespan have also used the temperature of the fluid in the pan.

Finally, there are some people who recognize the difficulty (and expense) of installing a sensor in the pan and thus install the sensor in the return line from the coolers to the pan. For example, the owner of Import Performance Transmissions in NJ (they do performance mods on imports) recommends putting the sensor in the return line from the cooler(s). In most cases (all steady state cases), the temperature in the return line will be very close to pan temperature since that line is the feed source for the plan fluid. The exception is during a long climb where the temperatures are steadily rising...or during a descent after a long climb where temperatures are dropping. In these situations, the gallon or so of fluid in the pan acts as a thermal buffer...it both heats and cools more slowly than fluid coming back from the coolers.

It sounds to me that the sensor in your Ford's transmission is just downstream from the pump...which takes fluid from the pan...so it is basically measuring pan temperature. Some domestic transmissions have a "test port" downstream from the pump and upstream from the valves, actuators and torque converter. It's possible on these transmissions to craft a fitting for this test port to measure the temperature there without all the issues of measuring pan temperature.

Bottom line is folks who want to measure TC fluid temperature don't understand the chemistry of degradation requires the fluid be too hot for an extended period. I've also noted that these folks are the ones who seldomly tow and who install a transmission temperature gauge primarily for gee-whiz and entertainment reasons. Putting the sensor in the output line from the TC will produce a much spikier temperature display (it will rise and fall everytime the TC clutch locks/unlocks) so it increases the entertainment factor. But those spikes are really false alarms unless the pan temperature is also getting too hot. And finally, the fluid that goes back into the transmission's guts is the fluid that's in the pan...if this fluid is too hot, the transmission can be damaged; if it's not, the transmission won't be damaged...even if the fluid going to the coolers seems too hot.

One other option to consider is an Aeroforce Interceptor. I got one of these recently and I love it. You can choose what two things you want to display, and have it there on a regular pod gauge for easy reading while you drive. Just don't try to change what is displayed while you drive
It picks up readings from the car's computer and displays them, so there is only one connector to hook up. Ignore the silver switch in the picture, that is left over from the last gauge I had in that spot.
http://www.aeroforcetech.com

[Bill]

OK, folks, we've had lots of discussions about the importance of transmission temperature, especially on long steep upgrades at high altitude. I've considered installing a temp sensor in the transmission pan as Rocky Mtn Ray did, but as I expressed above, I could never find a reputable shop that would do the work.

DCAIRNS never became a member, but I have to give him credit for finding and suggesting the Aeroforce Interceptor gauge. I've been suspicious about it - it seems too good to be true - but I've also been drooling over it for a couple years. After a series of emails between myself and Todd, the Aeroforce internet sales rep, I finally gave in to my lust and bought one last week. It arrived yesterday, and I did a temporary install today.

Wow! It looks great, and seems to do exactly what is promised! It can read out any two (user-selected out of about 20) directly-supplied engine/transmission parameters, including parameters like coolant temp. It can also display several calculated parameters like "miles per gallon" or "horsepower". I have mine set up to display transmission fluid temp (the thing I really care about) and mpg.

Besides the basic parameters, the thing can also read, record, and play back a bunch of race-track parameters like quarter-mile time, peak horsepower, and so forth. I don't care about those, but it can also read (and clear if commanded) the Diagnostic Trouble Codes (DTCs) that are present when your "Check Engine" light comes on. That can be quite valuable.

I don't have much experience with it yet, and I will repost when I do. But technology advances. This is a nice (and relatively cheap) alternative to the agony that RMR had to go through in order to get a temp sensor installed in the transmission pan in his Tundra.

Bill