DennisB

What is the "normal" operating temperature for an auto. transmission?
I'm having a trans. temp. gauge installed in my truck this week. But I have no idea what is considered normal. I haul a 28.5 ft 5th wheel. So I'd like to know approximately what to expect with and without that unit. I realize the temp. will vary depending on the terrain and outside temperature. But can somebody give me a "ball park" range, please.

By the way, the sending unit will be installed in the pan.

John Faughn

When I put my gauge in I thought the sensor or gauge were deffective becouse it never seemed to move then one day I was sitting at a long lite and I saw it move up to 100 f. , then I did some posts and everybody said that the cooling system is almost to good on these trucks and that that was normal , even
towing 8,000 lbs. it hasn'tgone over 100 yet , haven't been to the mnts. yet. From other trans. info I'ld read on most others that after 180 f. your getting hot enough to burn the fluid and start on clutchs.

HiJenks

I have the sender in the pan and pulling my 22' and a trailer I was running 100-150*. but on the real hard pull it got to 270*! the GCVW was 16,620# and I was in 1st at about 10-15 MPH for 5 miles.

Ted Jannetty has a poop sheet that gives a lot of info. I think I got it off of Geno's Garage site.

OTR PU

Don't know if everybodies "Normal" would be the same. I've had a couple different automatics. . .my ATS runs cooler than did my BD. I have a second cooler installed passenger side in front of the A/C cooler I think. Only seen it over 180* when I'm loaded with a camper or 5er stop'n'going through to and from workers going through cities. If I ever saw 280* I'd have a cat, pull off the road and turn it off. Both trannies seem to run about 5* warmer on average difference tween summer and winter. I try and run the deserts in the evening, on flats it rarely gets to 150*. But I start backing outta it when EGS's approach 1,200. Had enough stuff break already.

Cheers,
Steve J

kd460

Temps will vary with speed, how much the trans is shifting, load, etc. Probably the most important varience is from location of the sensor.

Where the sensor is located will change the readings drastically. As an example, John Faughns sensor is probably in the pan or in a pressure port just based on the temps he is indicating (no flame intended).

Personally I want to know how hot the fluid got. The fluid will start to oxidize (losing it's lubricating qualities) at a certian temp. If the over heated fluid leaves the tranny, goes thru the heat exchanger (gets cooler), then goes thru the tranny cooler (gets even cooler), then goes into the trans pan where the sensor is located, the temp I am reading has been significantly reduced. Based on the gauge readings, I never knew that the fluid reached a temp that caused it to oxidize.

So where to put the sensor? In the line that goes from the trans to the heat exchanger. This is where the fluid will be it's highest temp, as it is just leaving the torque convertor. It will give advance warning to pull over, pop in nuetral, and run the rpm's up a little to help cool things down.

If you really want to know how things are doing, put one sensor where I mentioned, and then another just before the cooled fluid goes back into the tranny. You can run two sensors with one gauge by just using a switch to go from one sensor to another. Can even run a third sensor to the rear diff, and with a 3 position switch, you can even get temp readings on the rear end fluid.

A rule of thumb I like to use is while cruising at a steady speed even with a load, tranny fluid temps should read within 100 degrees above the outside temp. Now, that changes with stop and go traffic, loads, etc. Also in the winter, your temps will be much lower.

Just my 2 cents worth. Kevin

HiJenks

I think I will put my other temp sensor in the output line to get a before and after reading.

from Dodge manual
TRANSMISSION FLUID TEMPERATURE
THERMISTOR
Transmission fluid temperature readings are supplied
to the transmission control module by the thermistor.
The temperature readings are used to control
engagement of the fourth gear overdrive clutch, the
converter clutch, and governor pressure. Normal
resistance value for the thermistor at room temperature
is approximately 1000 ohms.
The PCM prevents engagement of the converter
clutch and overdrive clutch, when fluid temperature
is below approximately 10°C (50°F).
If fluid temperature exceeds 126°C (260°F), the
PCM causes a 4-3 downshift and engage the converter
clutch. Engagement is according to the third
gear converter clutch engagement schedule.
The overdrive OFF lamp in the instrument panel
illuminates when the shift back to third occurs. The
transmission will not allow fourth gear operation
until fluid temperature decreases to approximately
110°C (230°F).
The thermistor is part of the governor pressure
sensor assembly and is immersed in transmission
fluid at all times.

I think that the sensor is reading the temp of fluid in the pan.....still think knowing the output temp will be good info.

zukgod1

Wow, that’s allot of really good info guys.
My sensor is in the pan right now but was formally in the line out to the cooler in the old trans, I had planed on moving it back to the output line as kd460 pointed out I would WAY rather know what it's running at rather than what the temp of the oil is in the pan.
I'll be switching the sending unit back to the accumulator this weekend and I will report the difference from the pan to the accumulator shortly there after.

Dan

infidel

On '94-'96 the sensor is in the hot line to the cooler, in the years after that the sensor is internal to the transmission right before the fluid leaves for the hot line.

The output line is the hottest fluid in the system, the pan is the coldest.
Seems to me a no brainer as to which location is better.
Would you want your coolant temp sensor in the overflow reservoir?

Eskimo

Hot line, mine's gone as high as 225° in traffic, but a tight torque convertor will do that to ya. once rolling, it's never gone above 185°, usually sits around 160-180°.

My old ATS ran cooler than this DTT trans, but the fluid coupling wasn't nearly as good, which accounts for the difference.

kd460

Eskimo, interesting statement: "Hot line, mine's gone as high as 225° in traffic, but a tight torque convertor will do that to ya. once rolling, it's never gone above 185°, usually sits around 160-180°."

I always thought the elevated temps were due to my sloppy stock torque convertor with 130,000 miles on it. What your saying makes sense, but wonder if the biggest problem is the poor location of the stock trans cooler.

Even the quality of the trans cooler is not the greatest, and it really does not get any air flow while going slow. No air being drawn thru it from the coolant fan as it sits way off to the side, out of the air flow created by the fan. I did a little searching last summer, and have yet to find a trans cooler that 1) is thin enough to fit behind the grill (more into the path of airflow created by the cooling fan). and 2) come with half inch tubing, 3) does not require financing

My temps sound similiar, I went so far as to buy an el cheapo 9" fan to fit over my tranny cooler. It is switched inside the cab, so when temps get up there (stop and go), I kick on the fan. Usually when things get close to 200, I will turn it on. If traffic is really slow, I'll even drop it into nuetral and bring the revs up a little. Seems to cool thing down faster, but the fan is not the cure all, it only brings temps down about 20 to 30 degrees. I always try to keep temps under 200, but the key word is "try".

Infidel, "Would you want your coolant temp sensor in the overflow reservoir?"
good analagy, I'm gonna use that. Kevin