W211 M271 burnt-oil smell after warm-up with a dry lower engine

Question

This W211 develops a burnt-oil smell after ten minutes at operating temperature, especially after stopping. The lower engine and parking area are dry. There is light oil staining high on the engine, but airflow makes the source difficult to follow once everything is hot. No smoke is visible from the exhaust.

Which upper-engine points on the M271 should be inspected first, and how would you keep an old spill from being mistaken for the current leak?

BavarianBits · Accepted Answer

Clean the upper engine first, then inspect the valve-cover perimeter—especially the rear corners and joints above the exhaust side—along with the cam-adjuster magnet connectors and crankcase-vent connections. Oil can travel along a harness or heat shield, so follow the highest fresh wet point rather than the lowest stain.

Run it to the temperature that creates the smell and use a mirror or UV dye approved for engine oil if the track is too fine to see. Also verify crankcase pressure is reasonable, because a ventilation fault can make a new seal leak again. A dry lower engine is consistent with oil burning off before it can drip.