Reduce Engine Oil Level

Just had an oil change and my mechanic put in 8.5..I drove 5km and that warning came on, went back he sucked out 0.5... and it came on again. I think it could be a sensor.
- and I just realized this is the C class section not the CLK. sorry! nevertheless same benz problem
hello
my w211 e220cdi has a puff of black smoke
the last ride I had a "reduce oil" red light, and after 5 min the light was going and not repeating anymore
can it be related with the black smoke ? or it should be too much diesel on the ratio with air?
thanks







