Most people don't realize this, but the majority drive with "severe service cycle", which is defined as short distance driving, stop-and-go traffic.

The service schedule for oil, as published by BMW, is doomed from day 1. It is a setup for sludge.

As the car gets older, the piston rings are more loose, there is more blow-by combustion gases etc. So the service interval needs to be shorter, IMHO.

My driving is 50-50 city-highway.

I use Mahle oil filter ($5/each) and Castrol Edge oil (Home Depot, or Walmart). Occasionally I use NAPA Synthetic oil when it is on sales.

- Summer: 10W30
- Winter: 5W30

The X5 has 120K, so I change my oil every 4K-5K. I will do an oil analysis soon, just to see the health of the engine.

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT