my experience with trans temps and gauges

[E2360]

I have read many threads on where to place trans temp probes and what the values mean. I am posting my observations on my truck for your info:



2003,2500HD, quad cab, Auto pulling 10000 pounds 3200 miles Chicago to Maine and back



Trans temp gages in upper rear test post AND in output cooler line BTW trans and water cooler.



Throughout the trip the trans port read 100-120 degrees on the highway, the output cooler line stayed about 140 at highway speeds and crept up to 180 when slower and in city traffic. During hard pulling up hill, the cooler line had an immediate response up to about 220 degrees with very little change in the trans temp gage.



during prolonged moderate speed driving the two temps did equalize at about 140 degrees. When I tested the temps in overdrive at highway speeds the cooler line (TC) temps fell to 120's with little change in trans temp 120"s



So what does this mean. one thing for sure, from what i've seen on this trip, if you depend on the trans test port temps to gage what is happening for torque converter output temps you will not have accurate data. Second, the trans cooler set up is very efficient at highway speeds and works well at slower speeds.



From now on, I will keep in both probes and use the cooler line temp as my base line. As an aside, a call to DC cust service stated to place the temp probe in the cooler lines.



Do not know if this info is helpful but it may change someones thinking and maybe save a trans.



Happy motoring!

 

[Bertram65]

Can you post a picture of what port you put it in? I have mine in a test port and my numbers are in line with your cooler line numbers. There is a picture of the probe in the port in my reader rig. Backing up I can see a 30 degree increase in under a minute. Running around town with a small trailer, 5k lbs it runs 195 and stays there. What kind of gauges are you using? are they both the same?

 

[BrianWalker]

Cooler line, Which one?

There is a small oil-water cooler at the back, driver side on the engine I see trans line going to, then it goes to the cooler at the front grill.



The manual says that the small (first) cooler has a temperature operated by-pass valve. Using coolant to help warm the fluid when cold.



Where are you sensors mounted? Pics please.

 

[E2360]

Photos to follow. need to figure out how to get them from the camera to the site... ... . I am much better at things that you can put a wrench on!



Di pricol gages both senders use same gage by way of a spdt switch.

 

[stevenknapp]

Hmm... . I emailed ATS and asked them. Their comment was that the output line would/should be hot. It's straight from the torque converter, which makes the most heat. From there it goes to the coolers. Then to the pan, then back into the trans.



Their concern wasn't for how hot the fluid out of the trans was, but instead what the rest of the trans got fed with. Hence the pan temp was prefered.



Seems to be a lot of opinion in this, but this made sense to me. Overheating is when the coolers can't do their job anymore and the whole trans gets hot.



Their second choice was a test port, the one that faces the rear of the truck near where the tailshaft bolts in.

 

[XcumminsX]

where are you from in chicago?

 

[Gary - K7GLD]

I had a guage on the AT in my '91 - it was used for towing - and my goal was to see as accurately as possible what the max temps were the fluid was exposed to. Various graphs on lifespan of AT fluid temps vs length of exposure are useful only when you know what THOSE temps are. If you are only wanting some form of "warm, fuzzy feeling" where fluid temps are concerned, then the cooler return line or transmission pan will probably give ya lots of comfort - but if you REALLY want to know what that fluid is being exposed to, the output line TO the cooler, right at the transmission is the place!



Since I was more interested in accuracy than false security, that's where mine was - and when towing in the hills or backing the trailer uphill, it got VERY hot - pinned a 250 degree guage!



YMMV!

 

[Stefan Kondolay]

I showed this post to Bill & he asked me to put up the following for you guys to have as a reference. We kind of take it for granted that everyone knows this because we do this day in and out. Here is a little info that may help you if you don’t already know the functions of the ports. When we install & recommend temp gauges for customers we only like to see them done in the transmission out line and if necessary in the pan. We prefer the outline as it is the most accurate but if a customer wishes the pan is the 2nd place. . With the exception of the 1995 and earlier model trucks. Since this is a 3rd gen. it is very simple.



The transmission cooler temp line we use for the 3rd gen is the custom line we get from Mass Diesel 1-508-660-7093. The second choice is the pan. However we do not recommend the pan for guys towing heavy or off road guys



Very briefly I will go over the test ports so you guys can get an idea of their functions and it may explain our recommendations and will also give you some tools when considering advice.



On the passenger side of the transmission there are 4 pressure ports and the driver side there is one port.



1st. or Front Port is the Front Servo Port; I have seen guys ruin their transmissions by putting a temp sensor in here. If your temp sensor probe is long enough it will actually make contact with the spring in the front servo, causing problems in 2nd gear apply cycle. This pressure port only has oil in it when you are in 3rd gear, & 4th gear. Since your transmission will build its max heat in 1st, 2nd, or reverse this pressure port is pretty much useless for accurate readings.



2nd or Middle port is your mainline pressure or what is referred to as your accumulator port, this pressure port has oil in it in 1st, 2nd, 3rd, & 4th but not in reverse. If you do not have an RV trailer chances are you are not going to overheat it when trying to back up your truck but if you do have a trailer again or want to monitor accurately it is a useless port.



3rd port is your low & reverse servo port. It is the one that faces towards the rear end. This pressure port has oil in it only during reverse & manual low applications. Making this pressure port pretty much useless to measure from as it has no oil in it during the 1st, 2nd, 3rd or 4th gear.



4th pressure port is the governor port. It is located about 4" above the 3rd pressure port. Basically this pressure port gets energized with vehicle speed. But it has no oil in it during reverse application.



# 5 pressure port is the 4th gear pressure port. It is located on the driver’s side of the transmission above the rear cooler line going into the transmission case.

It only has oil in it during overdrive apply. Hopefully after reading this you guys can see why we do not like customers using pressure ports to take readings from. A lot of customers use these ports because it is convenient; a lot of shops use these ports because it is a profitable & quick install.



If you measure your transmission oil from the transmission out line that is the hottest point to measure from . It also will give you a good indication of when to service your transmission. The best example I can give you is with reference to our own personal drag car. Most of time when we launch our drag car the temps are approx 275 degrees, but there have been times when we have exceeded 375 degrees, we know that it is time to change the oil as it is no longer any good. It has broken down and we can prevent damage by servicing. You guys may be surprised how high these trans can get to if you are trying to back up a big 5th wheel trailer. While it doesn’t mean you have wrecked your transmission it does mean the oil has been broken down. So from our point of view, don’t use the ports as they are not the most accurate point to do so from.



Hopefully some of this can help whoever got the advice to measure the oil from the reverse port. All of the above is verifiable by your service manuals.

 

[Bertram65]

Interesting disertation, not really sure how accurate it is though. I have mine, based on your description in port 3, I drive long distances frequently. Highway running empty I am at about 150 degrees, but when I hit traffic and get below 45 mph I can see a 20 degree increase in about 3 to 5 minutes. If there was no fluid there I doubt I would see that. I also see big differences in temp when towing, I am up to 195 in less than 10 miles towing 5K in traffic without ever backing up, once on the highway the temp drops about 20 degrees with the TC locked up. When I do back up (only with trailer attached) the temp increases very quickly sometimes 20 degrees in a couple minutes. These temp readings seem close to what others are seeing with pan mounted probes and line probes. How do you explain the temps when there should not be any fluid there? Here's a picture of the probe incase I am incorrect on which one you are calling it.

 

[JEly]

I have the massdiesel cooler line but I could not get my gauge to work when it was installed in the line-----------not sure what I am doing wrong but I have it now in a test port for now.



Jim

 

[E2360]

Photos

Attempts to send photos will not work. says file size is too large. Will try and decrease size. Sorry

 

[E2360]

photos...I hope

Photos of the trans sender in the pass side rear port facing the door and one of the sender in the cooler line

 

[E2360]

trans probe photo

Hope these help



Thanks to Steve St. Laurent for the help resizing the photos. Learned something new on the conputer but still would rather use a cutting tourch when it comes to resizing

 

[Snellville-Dave]

What I want to know is why DC doesn't already have a trans. temp gage installed from the factory. The GMC 2500HD's I've looked at have the trans. temp gage in the dash just left of the tach.

 

[BIG BOB]

Thanks Stefan for the explaination. Obviously Bertram65 in not familiar with the Kondolay name and DTT (Diesel Transmission Technology)

 

[Bertram65]

It really makes no difference to me who says it, if I don't agree with it I have no problem saying so. If there is no fluid at the port as described in the post I should not be getting any readings, or rapid changes as I am.

 

[Snow man]

Bertram 65,You will still get readings in the rear port ,but since the probe isnt in contact with a pressurized,or flowing circuit, the readings are likely low,and the guage is lazy in its response to actual temps. By the time your seeing the increase it already happened,and the trans case is just dissipating heat to that area ,and your seeing an increase,but it probably isnt the full increase,and if you had a guage in the cooler line or pan to compare it to ,you would see that either of those guages respond faster.

 

[bcpalmer]

Factory temperature sending unit

It is my understanding that our trucks have a transmission temperature sending unit from the factory. Where is it located? Brian

 

[Bertram65]

Snow man,

Perhaps but as I said I am getting changes in temp quickly if I get in traffic or if I am towing without ever going in reverse. For instance if I am on the highway running empty on a warm day, it runs around 150, then if I get in traffic, say 30- 40 mph it goes up to around 180 within 5 minutes or so, then once back up to highway speed it slowly goes back to 150. The changes going up in temp are allways much faster than going down. I will be putting on a PML trans pan and when I do I will get another sender and put it in the pan so I can see if there is a difference.

 

[Snow man]

Bert, as I said there's no doubt your getting the readings. Id like to compare the pan to where you are now. Aluminum is good at moving heat,so im sure your guage responds decent now as you said.