The problem with it being in the pan is you can have cooked the fluid and you will never know. The fluid is damaged long before the trans is from excessive temp, so you want to know if the fluid is good or not. Watching the hot line can save your trans from bad fluid, where the pan temp may not.

If its hot enough to need a cool down in the pan, it was probably hot enough to damage the fluid, but you don't really know do you?

 

Not to fan the flames, but how long does the fluid have to be at various elevated temps to damage it? Measuring temp at the hot line is measuring that transient temp. Measuring in the pan is, yes, the lowest temp, but it's also measuring something of a soak point temperature.

With the sensor in the pan you need to realize that the transients are higher than the pan shows, but, measuring in the hot line right ahead of the cooler is measuring a transient temp and 240 may not be a bad number as long as the number doesn't stay there. If it did, the pan temp would rise toward that, less the cooler's efficiency, of course.

 

Then you should be measuring the temp in the return line because thats the temp going into the system. Return flow from the coolers is used to lube and cool the drive train of the trans then gets dumped back to the sump. What your seeing on the test port is heat soak in the trans from engine heat, ambient heat, and fluid. There is no circulation of fluid at the test port.

Really, you have no idea what the trans is doing, how it is performing, or any idea how to adjust driving to compensate for high temps. Might as well take it out for all the good it is doing.

ATF+4 is rated to 320 degrees for 1500 hours and still meet the specs it was designed for. The real determinite factor is how hot is got for how long and how many times. This is what one measures at the hot line and how to keep that value low enough it doesn't prematurely hurt the fluid and the trans. The fluid will take a lot more temp longer than the trans, but, it needs to be changed more frequently if temps are consistently high.

 

I understand your point, but on the flipside, every time I tow the temps of the hot line would spike above "ideal" and I'm not about to start driving like a grandma because of it. That's why we change our fluid on a regular basis, right? Furthermore, I'm more interested in whether I've been driving so hard over a period of time that the whole system has heated to the point I'm doing constant damage to the fluid. In your scenario you might see 300F for 10 minutes while climbing a grade... but that doesn't mean any given molecule of fluid was AT 300F for the whole 10 minutes if the oil in the pan is still at 220. More likely, it was elevated in temp for a few seconds and cooled back down quickly once it hit the larger mass of fluid in the pan. Certainly if one were to interpret the data from each location with the same criteria they would be misguided. Perhaps ideally we would all have a temp gauge on the hot line AND on the pan, however I don't have enough room for the extra gauge nor do I think FOR MY DRIVING HABITS that it's a necessary investment. I won't say one is better in all cases than the other, and there's certainly nothing wrong with a hot line installation. Regarding your "might as well take it out" comment - I think we would all agree that either probe position provides data that if properly interpreted will enable much better monitoring and control of the transmission temp than Dodge gave us from the factory, even if you prefer one over the other! On a side note, since having UT rebuild my trans, the temp stays so low that I probably could go without any gauge at all!

 

Wow.. just wow!

If thats the case you need to spend a few bucks on another cooler!

And if that's your point of view why even have a gauge? There is an OEM idiot light...

 

Actually I've never had a trans overheating problem and am very happy with the stock trans cooler for my purposes. Just to clarify, the reason I used 'ideal' instead of a particular temp in that sentence was to illustrate the point that everyone has a different idea of what temp not to let your fluid go over. Obviously if it's so imperative to install on the hotline (per No_6_oh_no) the reason would be because a temp over 'ideal' would be seen before it would in the pan. I later used 300F as an example because of his statement that "ATF+4 is rated to 320 degrees for 1500 hours and still meet the specs it was designed for", not because I would ever actually see that temperature. He admitted in his post that it's a matter of temp x time, not just a momentary spike in temp that kills fluid, not that it's GOOD for it either, but it's going to happen from time to time and that's part of the reason you don't go 100k between trans flushes.

 

You can justify running the sender in the pan all you want, just realize its not the best method.

 

What is "ideal"? Better yet, when does the temp spike and what should you do to make sure it doesn't spike too high too long? Those question you will never answer lookig at pan temp until it is way to late to do anything about it. BTW, those are the questions that SHOULD be answered and give the driver the info to make pro-active rather than re-active decisions.


Actually, no. The main reason to service the trans fluid on regular schedule is 2 fold. First, the aromatics in the fluid that condition the seals and frictions are volatile. After so much time at operating temp they evaporate and the fluid looses its lube\conditioning ability for those important pieces. The fluid will quite likely pass all the viscosity and wear tests but thats not its complete job.

The 2nd reason, especially on a rebuild that uses the OE steels and frictions, is the steels make metal, very fine microscopic pieces that left in too long accelerate wear. The design of the frictions, steels, and fluid composition takes this into account hence the intervals.

Actually in lockup at road speed the trans is capable of circulating the fluid volume pretty close to 10 times in that period. So, yes every molecule of trans fluid is going to 300 degrees multiple times. If the hot line was at 300 degrees for 10 minutes the dash light would be on and it would be in limp mode. I understand your point but because you haven't seen the comparisons you don't know what you don't know.

In lockup the hot line temp is going to run 10-15 degrees hotter than the pan temp, thats all. Its pretty easy to see overall heat soak in that scenario. What you won't see is what is happening when the TC is in fluid coupling and be able to do something about it. There is no doubt, no misguided info when you see hot line temps topping 240 degrees.

What can you tell if pan temp gets to 190 degrees? Thats dead in the middle of the fluid operating range and you have no idea if it is the TC slipping causing it, clutch slip, or the hard parts going away. Now, put the gauge in the hot line and say you see 200 degrees. Still no big deal if your pulling heavy and hard in 90 plus temps, but, you see that temp running on the flat in 80 degree temps when the hot line normally runs 185 and you know something is up. Another scenario, 190 pan temp and 240 hot line now factor in your ambient and situation and you will be able to tell if that is normal by looking at the hot line and not have a clue looking at pan temp.

From personal experience, the hot line is not just a choice its the ONLY place to put the probe. I burnt the dirct clutches up in my stocker, my own fault but thats another story. I KNEW before any shifting or other problems manifested there was an issue. The EGT's jumped 150 degrees and hot line temps were up 10 degrees. No big deal but they had NEVER been that high in the conditions I was in. Had I not had the gauges AND installed them where I did I would quite likely been sitting in eastern Oregon in the dead of winter with a loaded trailer and smoked transmission. It ruined the input shaft but it could have been much worse.

To your point of misguided information, no way. Why do we install the EGT probe in the manifold and even as close to cylinder 5 and 6 instead of the down pipe? Because thats the BEST place to get the information. Why do we install fuel pressure gauge at the CP-3 instead of back at the tank? Because thats the BEST place to get the information. The exact same rule applies to trans temp.

Your free to put it where you want as it is your truck. However, my initial observation is still valid. Why bother if you don't put the trans temp probe where it does the most good?

 

Got a tee from napa and put it in the hot line. It's easy just cut out 1 inch of line.

 

Part number? NAPA here says they don't have anything that big.

Having trouble finding a steel compression tee online too.

 

I got mine from www.genosgarage.com.