On the Washington Beltway, in slow rush hour traffic, it is that hot outside -- at least as far as the engine is concerned. 
With 15W40, oil pressure at idle was near 0 at approx 95 degree coolant temp, and with drive engaged. Shifting to neutral raised it to between .6 and .8. At lower coolant temperatures, pressure was higher -- 1.0 and up.
Since this appears to be normal for this engine, I am not going to worry about it. 20W50 thins out quite significantly when heated, to almost the same extent as lighter oils, so I will stick with the 15W40 since that is what has been in the car forever.
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2008 E350 4matic / Black/Anthracite
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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black
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