As the title says my e550 is burning oil extremely fast. No visible leaks and no oil under the car. Since last summer I've had to top up oil twice. Any ideas?

 

Which cylinder(s) is/are scored? A borescope will tell the tale.
How many miles between top ups?
How long have you waited between oil changes? Once a year, no matter mileage, should be the absolute minimum.

 

Do you have oil in the coolant, how about coolant in oil?

You could have a leak at the oil cooler letting oil go in the coolant system.

Is your tail pipe very black? If engine burns oil the tail pipe tells about it.

 

Coolant was flushed at dealership in the fall, no sign of oil there. Had a coolant leak and I also didnt see any oil in coolant that was on my driveway. Tail pipe isn't extremely black from what I remember, picking the car up tmrw morning I'll have a look then

 

I will remember that point about the borescope as I have not had the issue diagnosed yet, just looking for tips for now. Picking up the car tmrw morning and it had a fresh oil change so I will keep track of how many miles the oil lasts. Have not had a regular oil change in a while, just been topping up but again I will keep track of that

 

How much is "top up"? Is oil being sold in "top up" size containers now? (lol).

 

The splash pan will prevent you from seeing anything anyway, at this age the oil cooler gasket will start leaking, cam sensors, cam magnets, PCV on the back of the engine

 

What's your oil change interval?

Mercedes says something like 1L per 1000km is "normal", which sounds insane and is definitely not normal in the sense that it's the experience most people have.

I probably add 1L per 4000miles, which still seems like a lot to me, but I do have some leaks I need to address.

 

I'm assuming it just went low enough for the sensor to trip and tell you to check the oil level at next gas stop and took about a liter to get it back up.

Two top ups in a year is not unusual for the biturbo V8s, it's just part of owning a turbocharged car.

If you're going longer than 5000 miles (8000 km) or 1 year between oil changes, stop doing that.