i left my E420 outside for the whole day yesterday (was 10-15 degrees out), and when i started driving, the car really struggled to shift gears. after the car finally warmed up a bit, the shifting got real smooth again. car's got OEM MB ATF .. i really do not want to leave the car outside anymore since im sure this si not good for the tranny.. ?

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Current cars:
2001 MB E55 AMG
2003 Honda S2000
2000 Honda CRV

Gone but not forgotten:
2004 BMW 325i 5sp sport
1999 BMW 540i sport
1997 MB E420
1995 BMW M3 coupe

Holding the gears longer to warm up the cats?

When does ATF freeze? I don't know 100 below?

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

The pour point is actuall a good indication of the "freezing" point, although it is not exactly the freezing point.

I doubt the hard shifting is caused by the ATF at that temp. LOL, I am in Big Rapids so it is colder than where you are. My (now sold) 87 300TDT (diesel) would start in any day. I miss that wagon.

It is probably caused by the delayed shifing (a feature) to warm up the engine as quickly as possible to reduce emission and increase fuel efficiency.

Mobil 1 ATF and probably most other synthetic ATF will provide reliable lubrication down to 130 degrees below 0.

I've seen a large increase in the number of complaints concerning transmission shift quality over the last couple of weeks. I'm certain that the recent cold weather (A.M. temp in the single digits) is to blame. Each day this past week, I made it a point to observe the shift characteristics every time I drove a car that had been sitting outside overnight. For my "test" I made sure each car was equipped with the 722.6 transmission, and I drove them in the "S" mode, not W/C. The "test" vehicles ranged from late-nineties 202's and 210's to a 2006 S-Class 4-Matic, with a few R230's and 211's thrown in. Not all of the cars I drove were in for transmission related issues. Here's what I observed. They definitely shifted differently when ice-cold. Most of them had a more than noticable 2-1 downshift when coming to a stop as well. After one or two runs through the gears they all returned to normal. Considering that the ATF is thicker, and all the moving parts (solenoids, check valves, pistons, etc) are moving a bit slower, I have to consider this a normal condition. Of course, warming a car up before driving in cold weather is always a good idea.

My 320 acts the same. When very cold the early upshifts seem quite delayed and the downshifts are earlier and more pronounced.
That is why I let her warm up for five minutes or so if below 20 degrees.
It does make a difference.
I also notice a slight "Whine" from the front (engine) just after starting in the same conditions but it quickly disappears.
Best Wishes,
Ron Y
2000 E320