Well, I've read about this happening in Benzes with synthetic oil, but never had it happen to me before.
I check my dipstick pretty regularly, especially since it has gotten cold and I am paranoid about burning oil while the engine is cold (it sure makes enough smoke). The dipstick had been reading pretty regularly at about 1/2 for months, untill monday at school I checked it and it was right at the bottom mark! No time to get oil, no spare oil, had to go to work, figured I'd check it again after work. After work it was the same. I know it should be okay since it was not below the low mark, but the poor 220 has to turn 3200rpm for 35 miles home, so I went to walmart to buy a quart of 5W40. I checked the dipstick for the third time that day after buying the oil and it still read the same, so I poured in 1/2 quart.
The next day the dipstick read at about half, which made sense, and I was kinda starting to think that I had just been having some oil burning on cold starts. That was untill today when I checked the oil before leaving school. Today the dipstick read completley full!
So, ? I'm not complaining, since it seems that I am NOT burning oil after all, but is it usually this bad? Really, this seems like my dipstick has been reading lower than actual all week! The odd thing is that I have checked it earlier this week after sitting overnight and it only read 1/2, but today when it read full, the car had only been sitting for about 5 hours. Is it normal for the reading to change like this for no apparent reason?

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1971 220D/4-speed ~250K mi. Family owned (dads side) through three generations since <5K miles.
1992 Chrysler LeBaron, 3.0V6 125K. Family owned (moms side) through three generations since new.
1977 Chevy Camaro Continual hotrod project
1970 Cadillac Sedan DeVille 472ci and nearly 19' long
1974 Fiat Spider Still needs work