Which ODBII transmission temp

dougman

Original poster
Member
Mar 15, 2012
20
Hi everyone,

I have a 2002 TB. I am using an Autotap scan tool to read my transmission temps. I have the GM enhanced data pack, so I am able to read all parameters. I see two temperatures for transmission. One says Transmission Oil Temperature, and one says Transmission Fluid Temperature. I am trying to calibrate a fan that I put on my external transmission cooler, but am confused as to which of these sensors is reading what. They are about 25-30 degrees different. Also, what is the "desired" fluid temperature? I just bypassed the internal cooler as it actually seemed to heat up the fluid on really hot days. My engine temp hovers between 230-240, and the trans would be right there or a few degrees warmer. Now I'm down to 180 - 210 depending on which sensor I look at.

I'm having Torque converter slippage issues at slow lockup speeds, but don't want to address that now. I've talked with a couple transmission shops, and they don't want to help me ream the TCC bore (which I think is the root cause) due to the high miles (180K). They just want to rebuild it. I'm trying to extend it's life as much as possible. I will be towing a 3K pound tent trailer next month from Salt Lake City to Yellowstone. I will take it easy, and watch my temps closely. I just don't want it to die while on the road.

My fluid is nice and clear with no discoloration at all.
 

ScarabEpic22

Member
Nov 20, 2011
728
Whoa! 230-240F ECT??!! Id do a coolant flush soon, its definitely degraded after hitting those temps (especially if regularly).

Never heard of the Tran Oil Temp, I use SAE.TFT or GM.TFT (Trans. Fluid Temp) when using EFILive.

ECT should be 199-207F depending on airflow and TFT should NEVER get above 220-230F. If it does, you're going to have major problems.

Look at the Superior TCC Powr Valve, have one in my 02 and coupled with the TCC PWM tables set to on/off vs gradual ramp-in, really helped the temps out plus I get into lockup much faster.

180K, yea I usually see the 4L60E needing a rebuild by 200K so anytime. Watch the temps, if the TCC isnt locking very quickly that could be the source of your overheating.
 

dougman

Original poster
Member
Mar 15, 2012
20
Scarab,

Thanks for the reply. My FLUID temperature never got above 185 degrees. The OIL is what seems to be high. My observations are strictly from in-town driving where the transmission gets very little opportunity to get into lockup. I'm going to take it out for a freeway drive where it will go into full lockup and see what my temps are. You can bet I'll be monitoring my temps the entire time I'm towing. My drive there has a lot of grade to it. I'll tow in 3rd and see if I can keep the TC locked up more frequently. I'm really surprised that my cooler isn't keeping temps even lower. It's a stacked plate - don't recall the brand, but it's 8"x 12" by 2/4-1". I just installed a 7" pusher fan on the front of it. Seems to move a great deal of air. I used an adjustable thermostat from Hayden with a long probe that I have run alongside the outgoing cooler line from the transmission. The fan kicks on at about 160 (FLUID temp). Never turns off, at least in city driving. We haven't had a day below 75 degrees, but we also haven't had a really hot day either. Those temps are also just the vehicle (and a couple kids + wife), no towing. I can't imagine what temps must be like on stock vehicles towing near GVWR on a hot summer day.

Thanks for the suggestions.

Doug
 

dougman

Original poster
Member
Mar 15, 2012
20
ScarabEpic22 said:
Whoa! 230-240F ECT??!! Id do a coolant flush soon, its definitely degraded after hitting those temps (especially if regularly).

Never heard of the Tran Oil Temp, I use SAE.TFT or GM.TFT (Trans. Fluid Temp) when using EFILive.

ECT should be 199-207F depending on airflow and TFT should NEVER get above 220-230F. If it does, you're going to have major problems.

I have always had high summer temps. I've flushed, replaced my fan clutch twice, but it still runs hot. This is also my second engine (first failed to do sleeve problems). In the summer, and especially in temps near 100, it's two tick marks above the middle. It gets as high as 3/4 of the gauge before the fan seems to even engage at all. I've long wanted to convert to an electric conversion with the Lincoln fan, or another ultra high flow fan, but just don't want to put big bucks into this vehicle. I need more room and don't see me keeping this for much longer as a daily driver.
 

Bartonmd

Member
Nov 20, 2011
545
Transmission fluid is the transmission oil. I'm not sure what you're reading, however the ENGINE oil temp is normally a bit higher than engine coolant temp.

Mike
 

dougman

Original poster
Member
Mar 15, 2012
20
Bartonmd said:
Transmission fluid is the transmission oil. I'm not sure what you're reading, however the ENGINE oil temp is normally a bit higher than engine coolant temp.

Mike

My Autotap has two temp sensors listed under the "transmission" section. There is no engine oil sensor. Both sensors indicate Transmission (fluid or oil) temperature. They seem to correspond, but have a difference of about 20-35 degrees.
 

ScarabEpic22

Member
Nov 20, 2011
728
Bartonmd said:
Transmission fluid is the transmission oil. I'm not sure what you're reading, however the ENGINE oil temp is normally a bit higher than engine coolant temp.

Mike
:iagree:

Theres no difference between Transmission fluid and oil, only trans fluid. Maybe AutoTap messed up and listed Engine Coolant Temp (ECT) as Transmission Coolant Oil. In the 4L60E I only know of the one temp sender, so I doubt one could be in the pan and the other in a different part.

Somethings wrong with your truck, when my 02 was all stock towing my 4100lbs boat from Seattle to Coeur d'Alene using 3 (330mi one way, sea level to 2950ft pass and back to ~1500ft, plus on the way back a 10mi 5+% grade at 50-60mph) Id get trans temps in the 220-235F range (bad!) and engine temps in the 215-220F range (also bad!). I have repeated this test over numerous years with similar results, then I added an external trans cooler and changed the tune settings. I can still skyrocket the engine temps if Im not careful, but I havent seen over 215F in a LONG time and usually trans temps dont get above 200F. The most extreme trips were fully loaded with 4 people and gear for a week, plus 100F+ ambient air temps. Ran the A/C the whole time except for pulling the grade.

I tow the same boat over the same trip with my SS now, first trip I took it 3 and got tired quickly of the high revs so I popped it into D. Temps were about the same as my 02 before the cooler, added a brake duct trans cooler and Ive seen 203F once in 95F+ ambient temps. Yes, 203F MAX towing (actually this was my other boat that weighs 4800lbs too) in D at 65mph, 4th gear + lockup.

What GVWR is your cooler? Mine on the 02 is 18k and I have it series after my factory 'cooler', think my SS has a similar rated one (whatever PCM4Less' brake duct kit is rated for, thats it). Your trans fan never shuts off around town? I have to actually work at getting my trans up to temp around town, usually takes me close to 20min of driving to get anywhere close to 160. Wondering if your trans is slipping more than you think and building a lot of heat as a result...

What gears do you have? That can make a big difference, if you have 3.42s then the engine is going to be working a lot harder to pull the same load. I have 3.73s in my 02.
 

dougman

Original poster
Member
Mar 15, 2012
20
I don't know the size of the cooler for sure, but I believe is is 18K. I know the two sensors are different from my engine temp as that is listed separately and is a different value than these two. I wish I knew which one to trust. I would have hoped it would be the fluid as it is the lower (more believable) of the two. As for the cooling, not sure what's going on. My cooling system is clean - I replaced my water pump not too long ago and it was clean as a whistle. I just think the design and response of the e-viscous fan is flawed and slow to respond. I'm ready to place a jumper across the connector to get 100% engagement for periods of high temp. I've never run my scan tool on the road except for once or twice (when I captured the high transmission temps). Driving from Death Valley to Southern Utah in 114 degree outside temps resulted in my engine temp being one tick away from red. I did stop to let it cool down, but it wouldn't go down past the 3/4 mark. It's always been this way, and with 180K miles and maybe another year left of daily driver duties, I'm not going to worry about it. I'll just watch the fluid reading and hope that's the right one while I'm towing. The nice thing about the route I'm taking is it quickly cools off maybe 10-20 degrees, if not more, before I begin the long climbs.

Thanks for your advise and experience.
 

Bartonmd

Member
Nov 20, 2011
545
dougman said:
My Autotap has two temp sensors listed under the "transmission" section. There is no engine oil sensor. Both sensors indicate Transmission (fluid or oil) temperature. They seem to correspond, but have a difference of about 20-35 degrees.

There is only 1 temperature sender in the transmission, and there IS an engine oil temperature sensor in the engine, and it can be displayed on the OBDII data link. I think they put the "oil" temperature under the wrong section. Should have been under the "engine" section.

Mike
 

AtlWrk

Member
Dec 6, 2011
674
Bartonmd said:
There is only 1 temperature sender in the transmission, and there IS an engine oil temperature sensor in the engine, and it can be displayed on the OBDII data link. I think they put the "oil" temperature under the wrong section. Should have been under the "engine" section.

Mike

For the 4.2L? This is the first I've ever heard of engine oil temp for our engine.

I'm not familiar with Autotap but can you see the PIDs associated with the temps? The one you want should end in "221940"
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
AtlWrk said:
For the 4.2L? This is the first I've ever heard of engine oil temp for our engine.
We assume everybody has an I6. Mike assumes we all have V8's. :biggrin:
 

dougman

Original poster
Member
Mar 15, 2012
20
Thanks everyone. I don't see anything beyond the description, but If there is an engine oil sensor, it would make sense. I did have things backwards - What is listed as Transmission FLUID temp is higher of the two. Even with my fan blowing 100% in 85 degree weather yesterday I had an opportunity to drive 10 miles under full lockup (70 MPH). The temp stopped rising, but it didn't lower at all. The temp listed peaked at 210. Is there any interpretation of these sensors? Is it a voltage signal that Autotap is coverting to a temp? Much like how no two pieces of hardware monitoring for PCs will read the same temp for the CPU?

I'm planning on using a little cool water on my cooler and see which temperature drops. I also think I will drain and refill with Dexron VI with a flush and filter change before I take this trip. I know fluid is moving well as the cooler is very hot to the touch. I just wish I knew which value to trust, and if I could trust that value.

I do have an I6 (sole reason I was interested in the TB to begin with).

Thanks again for the input everyone.

Doug
 

AtlWrk

Member
Dec 6, 2011
674
You are correct except that the PCM is doing the voltage-temperature conversion, not the scanner. The temperature sensor in the transmission is a basic temperature-sensitive resistor. Without getting into too much detail the PCM measures that resistance and converts that to a corresponding temperature based on the assumption that all sensors are created equal. This is then reported to your scan tool upon request.

That being said:
As the temperature increases the resistance goes down (negative coefficient) and vice versa so failures or increased resistance (e.g. from corrosion) tend to artificially lower the reported temperature, not raise it.
 

Bartonmd

Member
Nov 20, 2011
545
the roadie said:
We assume everybody has an I6. Mike assumes we all have V8's. :biggrin:

Correct. I assume everybody has the correct engine :biggrin:

Honestly, I haven't looked on Kyle's, when my Scangauge was hooked up to it, but my '07 5.3L has one, my dad's '00 5.3L truck has one, and the Cruze has one, so I had guessed that the I6 does, as well...

Mike
 

dougman

Original poster
Member
Mar 15, 2012
20
After letting my vehicle get nice and fully warm, I added all temp sensors, engine coolant, transmission fluid, and transmission oil. I then slowly ran cold water across the transmission cooler (remember I disconnected the transmission cooler), and found that the sensor that responded was transmission oil. It came down 25 degrees in a couple of minutes where the others didn't budge. At the time I started, engine was reading 201, transmission fluid 212, and transmission oil 185. At the end, transmission fluid read 208 and transmission oil 160. I'm happy as that was the lower reading gauge. My temps apparently haven't been as high as I thought. Would really like to know what transmission fluid temp is really reading as it certainly is an active sensor. I'll have to email autotap and see if they can provide me the actual sensor. In the meantime, thanks for everyone's input and advice. Been a very long time lurker (bought my early 2002 used in mid 2002). The longest I've ever owned a single vehicle.

Doug
 

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