Slight burning smell / faint fumes in ML cabin

[Smart320]

After driving about 25 miles today with heater and aircon on auto I get a faint but noticeable aroma of as if something is burning or could be oil fumes, goes when temperature is turned down. Car does not have a DPF ( 2007 320cdi ) Will get it checked out at service and MOT in 10 days time, but interested if anyone has any ideas of what could be causing it. No sign of oil under the car after being parked and nothing seen if bonnet raised when idling.

 

[wu56Shoozz]

I don't know if this will help or not but on the 270 engine (5 cylinder) fumes would leak into the cabin from 2 sources:

Breather hose on top of the engine would wear over time when the engine cover would rub through it..the rubber would melt /soften then hole allowing fumes into the engine bay and into the heaters...

The exhaust was of strange design and utilize a C clamp to connect to the manifold - this would break due heat/stress and again, fumes into the cabin that would disappear as you traveled..

Worth a punt just in case..

 

[Smart320]

Thanks for the suggestions, only have to drive home then tomorrow then car will sit on driveway until it goes to Cardiff for the service, but will see what I can see once I get it home