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...?