The problem may lie in the oil pressure sensor. Assuming, of course, that the problem isn't any unpleasant engine sounds but rather the oil pressure guages' slowness to move off 0 bar on start up. My OM602 engined w201 190d, with over 300,000 miles on the odometer, immediately pins at 3 bar upon start up, and the gauge only records a correct pressure reading after it has reached working temperature. MANN oil filters are the only ones I'll use.