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Unread 07-30-2015, 10:40 AM   #1
Mattyvac
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2012 KK Liberty 
 
Join Date: Sep 2010
Posts: 132
Trans fluid same level at diff temps?

I've been checking and making notes of my transmission fluid level in preparation for the oil and filter change at 70k miles on my 2012 KK. I do a lot of towing so I would like to do the change at this time.

I am using the oil dipstick and making marks on it with a knife, and using my laser thermometer to check the end of the dipstick immediately after pulling it out.

Checking the oil level after letting the car sit overnight and starting the engine for the firs time, running through gears, and then putting it in neutral on a flat surface gave me a dipstick reading of around 12mm of fluid at just over ambient temp which was about 85-88 degrees.

After driving for 20 minutes at 70mph on the highway and then sitting in a parking lot on a flat surface, I measured it again and it was now 26mm of fluid at 110-112 degrees.

One thing I noticed is that each time I lasered the end of the dipstick fresh from the bottom of the trans pan it would always read 110-114 when heated up. But when I put the laser thermometer on the outside of the trans pan it said 165-180 degrees! I'm not sure how there can be a huge temperature swing like that between the fluid and the pan? All I can think of is that the pan is acting as a heatsink and shedding heat through the outside while my tow package trans cooler is keeping the fluid inside cool and cycling it....

According to the trans level chart my oil is supposed to be an average of 10-12mm higher than it's currently reading. Did I really lose that much oil?

When I do the trans service- should I just replace what I measure that comes out of it or should I add more in case some evaporated over the last few years?

I've been reading about the 42RLE and it seems it likes a slight overfill sometimes...?

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Unread 07-30-2015, 01:48 PM   #2
tjkj2002
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2002 KJ Liberty 
 
Join Date: Dec 2009
Location: Colorado
Posts: 8,257
The fluid in the pan will always be cooler then the fluid in the trans is.The pan will always read higher also since it's dissipating the heat from the trans case.

You need to really read the trans temp via a good scanner that has Chrysler's trans PID(very few and high $$$$).
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Unread 07-30-2015, 06:28 PM   #3
Mattyvac
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2012 KK Liberty 
 
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Posts: 132
Quote:
Originally Posted by tjkj2002 View Post
The fluid in the pan will always be cooler then the fluid in the trans is.The pan will always read higher also since it's dissipating the heat from the trans case.

You need to really read the trans temp via a good scanner that has Chrysler's trans PID(very few and high $$$$).
Well that's not happening lol

All of my expiraments point to my trans fluid being very low. So either way...

As long as I measure what I remove during the filter change, re-add that, plus about 1/2-1QT I should be good to go.

I will also obviously do measurements like I have been doing now and add fluid if needed.

Even without the official temp gauge; I know that when I start my car in the morning after sitting overnight and letting the car warm up for 2-3 minutes...the fluid is no more than 90 degrees at that point. And if I'm 10mm low already with that KNOWN temp...I need a fill ASAP.
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Unread 07-30-2015, 08:55 PM   #4
avatr
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Join Date: Mar 2014
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if I'm understanding what you wrote - no matter when you check the level, it's low.

maybe it's just me, but I don't think I'd drive around with low trans fluid.
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Unread 07-30-2015, 09:21 PM   #5
tjkj2002
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Quote:
Originally Posted by Mattyvac View Post
Well that's not happening lol

All of my expiraments point to my trans fluid being very low. So either way...

As long as I measure what I remove during the filter change, re-add that, plus about 1/2-1QT I should be good to go.

I will also obviously do measurements like I have been doing now and add fluid if needed.

Even without the official temp gauge; I know that when I start my car in the morning after sitting overnight and letting the car warm up for 2-3 minutes...the fluid is no more than 90 degrees at that point. And if I'm 10mm low already with that KNOWN temp...I need a fill ASAP.
Only way it can be low is if you have a leak,ATF does not just disappear. and if it's 12mm "low" that is enough to effect trans operation.

Use the correct tools or you will get false readings.Those charts your reading off it based on the trans temp sensor reading which your not taking into account thus throwing off your readings.
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Unread 07-31-2015, 08:02 AM   #6
Mattyvac
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2012 KK Liberty 
 
Join Date: Sep 2010
Posts: 132
Quote:
Originally Posted by tjkj2002 View Post
Only way it can be low is if you have a leak,ATF does not just disappear. and if it's 12mm "low" that is enough to effect trans operation.

Use the correct tools or you will get false readings.Those charts your reading off it based on the trans temp sensor reading which your not taking into account thus throwing off your readings.
Good point.

There is no transmission leak on the vehicle. If you're saying ATF doesn't evap like coolant would - then my readings are 'correct' rather than 'low' and I'm just reading it at an odd temp.

My trans is working fine right now. No odd sounds or anything and operation is normal.

I'm going to measure what was removed during the filter change and replace only that amount back in plus maybe a .5 qt more. That should be just fine.

Thanks.
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