I recently flew MAD-MIA on one of IB's classic 747. A few hours into the flight, I noticed a stream of blue-ish smoke coming out of a little vent on the side of the outboard engine. I started freaking out a bit and shut my sunvisor closed. A few minutes later, I checked again and the smoke had dissappeared. Some minutes later I looked again and it was coming out again.
We landed at MIA without incident, and at no point did the FAs or pilot advise or do anything out of the ordinary, so I assume this was a normal event. Anybody has any idea of what this was? Sorry if it's a dumb question, I just never noticed this before.