The N63 is the 4.4 twin-turbo V8 in the 550i, 750i, X5 50i and X6. The turbos sit in the valley between the cylinder heads, close to the heat. That layout is why these engines have a name for oil use, and why a cheap early N63 can become an expensive engine after it is fitted.
Why it uses oil
On early N63B44A engines the valve stem seals harden and the engine drinks oil. BMW later revised the seals, the turbos and the cooling on the TU and TU2 codes, often written N63B44O1 and N63B44O2. A car that needed a litre of oil every thousand kilometres may already have had the seal job, or it may be the reason the engine is out. Ask which.
Which code
The letter and number after N63B44 matter. An early A engine and a later O2 engine do not share the same turbos or the same cooling pipes. The car's computer is coded to the engine it left with. Send the VIN. We will not guess from "550i".
What the photos should show
Look at the valley, the coolant pipes across the front, and the oil pan. White crust at a coolant joint means the pipe has been leaking. Oil baked onto the turbos is common on a used hot-V and is not, by itself, a failed turbo. A cracked charge pipe or a turbo with shaft play is a failed turbo.
Fit the engine with new coolant, new oil and a cooling system that has been pressure-tested. An N63 that runs low on coolant will be back out of the car.
Full N63 guide · N63B44O1 from a 550i
Coolant and oil after fitting
Use the coolant the later N63 was designed for, and vacuum-fill it. The pipes across the front and the valley are the joints that weep after the first heat cycle. Look at them again the next morning.
Check the oil level after the first run and again after 100 km. An N63 that is a litre down and was not checked will be the engine that "failed" the following week. Tell the owner the early engines use oil, and tell them to watch the level, so a normal habit is not mistaken for a disaster, and a real leak is not ignored.
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