Why does the fluid level rise as it warms up again?

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

Another way to check temp on a 722.6 is to use a digital volt meter on the temp sensor wire at the trans controller. ( hook the neg lead to trans controller signal return. ) You will have to look for a volts to temp chart or generate one.

The highest temp is the outlet of the cooler due to fluid coming from the torque converter. The .6 sensor is in the pan and what the fluid level chart is based on so I'd go with that.

I measure my ATF temperature when filling using a thermocouple that can be inserted down fill tube. It reads out on my DVM. Picture below. I run it through a small plastic tube which I use as the dipstick.

By the way, if you use a home made or ebay dipstick instead of the MB one, be aware that it likely goes to bottom of pan while MB one stops about 5mm from bottom of pan.

Another learning. Driving car for 20 miles won't heat ATF to 80C. I once measured mine after long trip and it was at about 65C. At idle in garage it gets closer to 80C (in winter may have to block radiator)

IR thermometers can give incorrect reading depending on surface being measured. Cleaning off oil and sticking a piece of masking tape on may help get more consistent relative, but perhaps still not accurate readings. (Have used these in industry and found this out even using $1000+ units. )

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5