Nearly ten year old motor with less than 20k miles. The first problem is that it isn't driven enough.

The second problem probably is that the oil isn't changed enough. I'll wager the car doesn't even reach oil operating temp ever.

The reason engines sludge in later models is a weird combination of issues. The manufacturers designed service intervals so long that people were having to place oil into the engines between changes. People don't like that. So manufacturers decreased the scavanging effect (reduced flow) of crankcase ventilation systems. Most of the oil used in a modern engine is breathed into the combustion process through crank case vapors.

By reducing vapor flow they reduced oil consumption and they seriously increased the residaul effect of water vapors condensed and harsh combustion gases blow by the rings. These gasses turn water and oil into acids. in a robust pcv system these products would be scavanged properly, but for systems designed for wimpy consummers they created a problem. That problem is exaserbated by long (time based) service intervals and driving conditions that involve short trips where the oil doesn't reach operating temp.

My wife and I live less than a mile from work. My 2004 545 BMW has had 9000 miles put on it in the 2.3 years I have owned it. I change the oil every 6 months which means about every 3-4000 miles. I also drive around an extended block on cooler days to atleast get the cooling system to operating temp.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician