Hi all. My Optix full sweep transmission gauge quit working and I'm looking into a Maxglow replacement. I placed my Optix temp sensor in the port recommended by dieselsite. Since a new gauge comes with another sensor and I saw a two temp gauge set up on YouTube, I thought I'd confirm the cold and hot temp probe spot locations on the transmission, if they exist. I know my current probe is on the drivers side of the transmission. Not sure if this is a line for return from the cooler or going out to cooler from the transmission. Either way, this could show me how effective my cooler is working and give me a dual use gauge. Thx!

Video for dual gauge idea below.
http://youtu.be/dwWxvBApfRc

 

There is one port on the transmission. You have your sender there now. It is neither the out to the cooler nor the return from the cooler.

 

So that port is just the transmission temp at its hottest than. That is simple. Maybe I can find a way to install an inline port or "T" on the cooler line?

 

Not quite.

Mark may have been a little coy with his factual answer, and your conclusion was a little bit of a stretch beyond what he said.

The driver's side port is a pressure test port. It was designed for a service technician to attach pressure test equipment, but it happens to be a handy threaded port for a temperature sender as well, so that is why it is so commonly used in the 4R100 for an aftermarket gauge.

The temps that are sensed at the pressure port are not the "hottest" the fluid can get, but they are consistent with what the factory transmission temperature sensor sees and reports to the PCM. A distinction should be made here between the higher resolution of temperature readings the PCM sees, versus the dampened temperature reports on the factory dash gauge for 2002 and up models.

Anyway, what you are likely thinking of with "hot and cold" is the difference in transmission fluid temperatures between the inlet line (after the fluid has been cooled) and the outlet line (from the torque converter, where the fluid has been worked the hardest, and acquires it's highest temperature). The hot outlet temperature is not the transmission sump temperature, because the outlet fluid hasn't had an opportunity to get cooled yet.

In the old days (well, 20 years ago), it was popular among the OCD type of infomaniacs to plumb an inline T sender port into the outlet line, to read the hot temperature leaving the torque converter, as a predictive indication of when the fluid was really being sheared and worked hard. Then, to monitor the effectiveness of the transmission cooling system, a second inline T sender port would be plumbed into the return line, after the fluid has been cooled.

The thing is, both the output and the return lines are on the passenger side of the transmission, which is one reason why Mark knew that your sender had neither the hot nor the cold fluid temperature. The second reason being that Mark worked as an automatic transmission calibration / testing / cooling engineer for Ford, and has dealt with hundreds of thermocouples and senders on Ford automatic transmissions... so he kind of knows what he is talking about.

The risk of adding more failure points increases once you start cutting into the inlet and outlet lines of the transmission cooling circuit. That is why you are better with the single sender location, screwed directly into the transmission case itself, that you already have. This way, you are reading the transmission temperature that the transmission valve bodies, friction materials, and gears are actually working with on average, after the fluid has returned from the cooling circuit and mixed with the fluid still present in the sump, and before it gets really heated again in the torque converter on it's way out.

There is no point in stressing about how hot the torque converter heats up the fluid... because as long as that heat gets dissipated through an effective series of heat exchangers that do not restrict flow, then all is good. You'll have sufficient early warning when the temperature of the fluid that the transmission is actually working with (what you are reading now) begins to climb past 225 degrees F for a sustained period of time.

Too many gauges have the potential to be just as bad as not enough.

 

Yep, that's what I would have typed if I hadn't been too lazy.

 

Thanks guys! That all sounds great and makes sense to me. I figured if I could double dip with the extra sensor, why not? But simple is also good and that works for me too! Thanks again!