2005e320 Cdi
I get 2 readings. "Oil level ok"; engineering mode says oil level "5.7"qts
I added a qt a few weeks ago but have since then made 2 high speed trips. Maybe a total of 1k miles is it normal to burn a half qt with sustained 70 mph
Driving? Is it ok to wait for the "add oil" or better to keep the engine topped up?

A high speed run may burn some extra oil. Is the oil getting old? It might burn out sooner if near the end of its life. Also you might get some condensed water in your sump from driving around town. A good trip will evaporate that as the engine gets good and warm. As for level, I'd tend toward keeping it up near the top.....but not overfilled.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I have found that the precise oil level reading can vary, even when I make every effort to ensure that all variables are identical.

However, 5.7 does sound low. I would expect to see something in the 6.8 to 7.1 range.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

On OM 61x engines, chasing the high level mark on the dip stick would lead to excessive oil burning. This oil consumption would immediately stop when the oil level was left at the mid-point.

I don't think the newer engines exhibit this, I have not found it to be true for my OM60x engines.

Nevertheless, I would be leery about trying to keep the oil level at the high end.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

You can get a service dipstick and check it the old fashioned way and know for sure what's in there.

I'd look into switching oil brands/weights at your next oil change. It doesn't appear Castrol 0W40 Synthetic is the best choice for your CDI (even though approved). For now I'd top up to 6.5 qts (displayed with the engine off and after sitting overnight) so you have a baseline and monitor the level. (Note: The actual amount of oil in the engine is approximately a 1/2 qt higher then displayed, unless checking the level BEFORE starting the engine after an oil/filter change)