'Hot wax' smell?
 

A '91 190E 2.3. After running for awhile, the car developes a smell I would describe as that of hot wax, likely from the engine compartment and pulled through the vent system. The engine temp and fluid levels stay normal. The smell in not at all like burning oil, fuel, any coolant I have experienced, and I have not found any signs of anything melting. Closest I have found on another car is when a plastic bag had melted onto the exhaust.

Any ideas? Thanks.

Steve