Transmission temperature

[SoNic67]

Now, that the colder mornings are in, I did a reading on my transmission temperature.
Outside temperature - 38-40F.
Transmission temperature slowly climbed to reach 120F after a 25 minute drive - half on highway. Stock cooler, OBDII reading.
Is it true that the TC will not lock-up if temperature is below 150F??

I am looking to find a way to keep it from cooling while is not at that temperature - maybe a 3-way thermostatic valve...

[Breeves002]

I guess you have an external cooler installed? I don't know the exact temp, but it is true TC won't lockup if it is not warm enough. Install a cooler that is made not to over cool (has that valve built in). That valve would work, it would bypass the cooler unless the temp is high enough.

Where are you taking your temp reading from? Did you verify TC didn't lockup?

[SoNic67]

I have the stock cooler on '96 Sable. Reading is via OBDII.

[Breeves002]

I guess I don't understand how the third gen coolers work. Is it the same as gen 4 or are they bigger? I know mine is just a pipe. I also didn't know that you could get the temp reading through OBD-II, can gen 4 do that as well? Hah! My scan tool supports a LOT of PID's, but I've never seen a trans temp reading.

If it is stock cooler and is the same as mine, it is possible your actual temp reading is lower than it really is. Did you confirm TC isn't locking at that temp? Someone will have to chime in and tell us what the temp for the TC to lockup is.

[behlinla]

Did you rig your fans to be on all the time? Are all the air dams in place? The coolant temperature is also used to determine whether the torque convertor will lockup.

[Jeff K]

It is NOT TRUE that converter will not lock up until TFT hits 150. Think about it.... during the summer after a cold start, TC locks nearly immediately.

There is a lookup table in the PCM of IAT (which the PCM takes as the ambient temp) vs minimum TFT for lockup. I forget the exact temps, but the lower IAT is, the higher the min TFT for lockup. ECT may be in there somewhere also.... I forget.... been a long time since I have seen the tables.

This is kind of like the long standing internet myth that the PCM wont go closed loop until the engine hits 180 to 190 deg.

[SoNic67]

Well, I would be happy to see those tables. On highway, TC locked (I think) when temp was over 120F. It might lock earlier, but before that I was in a traffic that wasn't prone to TC lockup
The issue that I see is that transmission temperature climbs VERY slowly compared with engine temperature. Fans are not on, the low speed fan comes on at 210F (coolant temperature). I don't think there is a thermostatic valve for the transmission oil. In cold mornings, the transmission oil gets over-cooled.

PS: With my OBDII reader I found out that Ford has temperature sensors in their transmissions but GM doesn't (unless is Allison heavy duty). That reader is the best toy that I got for only $12!

[Breeves002]

What reader do you use and how did you get it for $12? I found out my scan tool supports almost everything under the sun, except transmission temperatures. Of course.

[behlinla]

Yes, could you tell us what model scan tool you are using and which software? Transmission fluid temp is not part of the normal OBD-II parameters, so are you sure you're reading ATF temp and not something else? The only way I see of reading it outside of proprietary software is perhaps by reading mode $22 data.

Also, are you sure the temperature units are in Fahrenheit and not Celsius? 120ºC would be a more reasonable fluid temp (248ºF).

[JW657]

Originally Posted by behlinla

Yes, could you tell us what model scan tool you are using and which software? Transmission fluid temp is not part of the normal OBD-II parameters, so are you sure you're reading ATF temp and not something else? The only way I see of reading it outside of proprietary software is perhaps by reading mode $22 data.

Also, are you sure the temperature units are in Fahrenheit and not Celsius? 120ºC would be a more reasonable fluid temp (248ºF).

I'm still trying to wrap my head around how it could be 120F after 25 minutes of driving. It doesn't seem quite right to me.