I searched this forum but couldn't find an answer...
I just installed an Autometer Colbalt electric tranny temp gauge (100-260F full sweep) and installed the sender in the port just fwd and above the selector on the drivers side (E40D). I have a tow package on this truck. When I drive it, it takes a long time to warm up the tranny. It was about 75F outside this morning and on the 8 minute no stop-and-go drive, it was barely above 120. Yesterday, I left work and it was 100F outside. I did about a 15 minute stop-and-go drive and it was 180F when I got home.
Does this sound right?
A) Does the fluid take a long time to warm in an unloaded truck with the tow package?
-or- B) Is the sender slow to show temp chages?
-or- C) Is the sender only indicating the heat transferred from the case to the sender and not the actual fluid?
I haven't pulled a trailer with the gauge on yet but I'm a little concerened that the indicated temp may be very delayed and I could overheat the fluid before the gauge indicates a problem.
Should I get a manifold and install it in the output line to the cooler?

 

If it helps, my '01 5.4 Scab w/4R70W/big radiator and trailer tow runs about 70* over ambient(close to your numbers). It takes about 30 min of driving to heat up all the way. I used the Cyberdyne digital temp gauge with the sender in the same location as you.

There's several different opinions on sender location.

 

I've got an Autometer electric trans gauge too, but mine is in the trans output line to the rad. So it's seeing the hottest temps right after the TC is done with it.

In the mornings, it'll take a bit to get the needle to move. Mostly because I've got very little stop and go before hitting the freeway, then it's a 65 mph ride for 15 miles. The needle barely moves on cooler mornings

Coming home, and it's warmer out and I'm stuck in traffic, the temp will get to 150* pretty fast. 180* when it's really hot and really slow going. Once I can get into third and the TC locks, the temp will go down.

I think what you are seeing is the effect of your tranny cooler..... When you are cruising, the cooler has lots of airflow and since your sensor is inside the trans, it's reading that cooler temp.

Once you slow down and are in traffic, not so much airflow and the cooler is not really doing much to cool the fluid.

That's basically how mine goes too. Even with the sensor in the line. When I've got the airflow AND the locked TC, my inline temps are probably the same as the trans itself..... Once the airflow is lowered, or the TC unlocks or is in 1st or 2nd, that's when I see the higher temps. Moves pretty fast too.

When I tow my #4500 TT, my temp will sit at 150* while cruising on the freeway on level ground. As long as I can keep it in 'locked' third, the temps stay low. If it happens to unlock in third or I'm pulling a hill, the temp will rise, since I'm basically seeing the TC temps with the sensor placement on my rig.

Mine has gotten as high as 195* in stop and go traffic on a 90* + day and not towing anything!!

I'm really considering getting one of Mike T's coolers with the little fan on it that will kick in at 180*. Since the only time that seems to occur is when I'm in traffic and not moving.

As far as "where" to place the sensor, I don't think there is a true "correct" place to put it. You can come up with valid pro and con reasons for either place IMO........

I guess the perfect solution is to have two sensors. One in the trans and one in the output line and have a toggle switch to the gauge and read either one depending on the driving situation??

I do like the fact I know that the temps I'm seeing are before any coolers, so when the fluid does make it back to the tranny, it "should" be cooler inside the trans then what temp I'm seeing......

 

I have a 97 Expy with the E40D and installed an Autometer electric gauge in the pressure port where you have yours. I put my gauge in last winter and thought the sender was bad because in my 12 miles of freeway driving to work the gauge would just start to come up when I got to work.
When it got warmer out the temp came up faster and now takes about 10 miles to get to full temp which on long freeway trips is 150 or so. City driving on a 95 degree day is routinely at 175 degrees. I'm also a lead foot in town too so that doesn't help the tranny temp either. Sounds like yours is working like mine.