Also, because it has been so hot here (Wash. DC Metro area) this summer, the heavier oil makes good sense.

The 20W50 appears to be causing cavitation, evidenced by the occasionally erratic pressure guage needle, as described in another oil thread. Reverting back to a lighter weight will resolve that (my guage did not do that before).

Since the below-1.0 pressure readings are normal, so long as pressure shoots straight to 3+ on acceleration, I will not worry about it.

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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