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tjd2943 · 05-04-2013, 08:30 PM

Does anyone monitor their trans temp? I have a 2012 Yukon with the heavy duty towing package and pull a 6,500 pound Passport. On a cool day I'm at 180. Hot day 235. Friend of mine has a Tahoe that is consistently 25 to 30 degrees lower than mine on the same days, same trips. Any insight or personal experience?

Skip426 · 05-05-2013, 12:20 AM

You have to look at absolutly everything, including the gauge accuracy. If running empty his temp is lower then it's possible your gauge is reading high or his low.
Also , use of A/C , bug screens, grill chrome, operation of thermostatic rad fan, use of synthetic trans fluid, driving style.
As a rule of thumb, in town traffic, stop & go , because the oil to air aux trans cooler is getting very little air flow, trans temps and engine temps should be equal , because the trans oil is only being cooled by the oil to water cooler in the rad. As vehicle speed increases and more air goes through the grill the oil to air cooler becomes more efficent and trans temps can be lower the engine, if your running empty.

tjd2943 · 05-05-2013, 12:47 AM

Thank you for the reply. That all makes sense. Confusing part is we have similar trailers, take trips together so driving conditions and style are similar and mostly highway. Is 240 on a summer day OK? Neither the manual nor the dealer can indicate what a normal or high temperature would be.

RV Wizard · 05-05-2013, 03:49 AM

We are glad to have you join us here and we look forward to reading of your adventures and experiences. I am sure you will enjoy the website and forums. Good luck, stay safe and keep us posted.

Skip426 · 05-05-2013, 09:15 AM

Quote:

Originally Posted by tjd2943

Thank you for the reply. That all makes sense. Confusing part is we have similar trailers, take trips together so driving conditions and style are similar and mostly highway. Is 240 on a summer day OK? Neither the manual nor the dealer can indicate what a normal or high temperature would be.

Somewhere in the Allison trans forum, the numbers were posted, I'll look for them. I think you should have a warning light as well as the gauge; check your owners manual; if the warning light is not coming on and the trans fluid is not discolored, you should be OK.
Isn't there a red line on the gauge?

tjd2943 · 05-05-2013, 09:31 AM

Thanks again, Skip. I don't have a trans temp gauge. It is one if the digital readings on my dashboard menu. I've never had a warning come on but it makes me nervous!

Skip426 · 05-05-2013, 09:58 AM

OK, I just got back from the Allison web site; Links in the first post in the Allison trans forum;seems you have to know the exact location of your trans temp sensor, because the allowable temp max is different.
If the sensor is in the sump ( trans pan ) then the max is 250f.
Sensor in the output line trans to cooler; my Dodge P/U sensor was in this location; max is 300f. These are Max intermittant temps.
Sensor location is something that may be different between the two trucks, also the posibility of sensor inaccuracy can't be rulled out.
The cooler line location gives temps of the fluid leaving the convertor; the hottest place in the trans; before the cooler, the sump location is after the cooler.

SmokeyWren · 05-05-2013, 10:30 AM

Heat is the tranny killer. If you allow your tranny to overheat, then it's going to have a shorter than normal life.

First rule is you need an accurate tranny temp gauge that gives you sump temp, or very close to sump temp. Then never allow more than 225° tranny temp.

If your truck has the option to show tranny temp in the digital readouts on the dash, then you need to find the sender and test it. Put the sender in boiling water, and it should show the temp of boiling water at your altitude. If you're near sea level, then it should show 212°. If it's not accurate, replace it with a sender (sensor) that is accurate.

Regardless of brand of tranny, they all use ATF, and ATF is your limiter. Over 225° sump temp and the ATF deteriorates in a hurry. If your tranny temp sender is not placed in a location that shows sump temp, then you need to know where it is. On a Ford pickup, it's in the valve body, so the temp there is about 15° higher than sump temp, or a max tranny temp of 240°. Ford says a max of 245°, but that's not a conservative temp that will allow a long tranny life. If your manufacturer says up to 250°, then I wouldn't allow mine to get close to 250°. Or if it did get up to the red line, I'd change the ATF ASAP, using procedures to change all the ATF (not just the ATF in the pan), and use synthetic ATF from now on. Synthetic ATF can handle more heat without deterioration than dino ATF.

tjd2943 · 05-05-2013, 11:50 AM

I'm good around the house but not much experience around an engine. Is the sensor generally easy to find and get to?

SmokeyWren · 05-05-2013, 02:59 PM

Quote:

Originally Posted by tjd2943

I'm good around the house but not much experience around an engine. Is the sensor generally easy to find and get to?

I don't know about a GM. On a Ford, you have to remove the tranny pan, then the valve body is right there, and the temp sensor is in the middle of the valve body. You probably need a good shop manual to find it.

bartlettj · 05-09-2013, 09:24 PM

Get an infrared thermometer, then one day when you are towing pull over and immediately check the pan temperature with the thermometer. Then you don't have to take the trans apart if it matches the gauge- you need to fix the fan clutch or clean the bugs out of the transmission cooler.

SmokeyWren · 05-10-2013, 07:22 AM

Quote:

Originally Posted by bartlettj

Get an infrared thermometer, then one day when you are towing pull over and immediately check the pan temperature with the thermometer.

But do that right after you have climbed a mountain pass or long steep hill where the tranny downshifted and the torque converter unlocked. Pulling a heavy trailer up a grade with the torque converter unlocked is a very severe condition for getting the ATF boiling.

The most severe conditions for overheating an automagic tranny? Dragging a heavy trailer up a slow mountain trail where you cannot go fast enough to keep the torque converter locked. On a Ford that's around 40 MPH.

Pulling a heavy trailer down a normal highway on the flats at speeds over 45 MPH shouldn't cause tranny sump temp over about 180° or maybe 190°.