BMW boxer engines (the OILHEAD version) are merely glorified lawnmower engines resembling half of an old VW air cooled 4-cylinder engine but fitted with some rather interesting cylinder construction. The cylinders on oilheads are aluminum WITHOUT steel sleeves. Nikasil, a process of depositing nickel, silicon carbide on the aluminum cylinder walls is used in place of costly sleeves. This provides several benefits;
1- Cylinder walls are not wear items in the oilhead engine.
2- These cylinders cool better than steel lined cylinders.
3- Reliable, long life ring to cylinder wall sealing.
What this design does NOT like is detonation due to low octane fuels or poor engine tune.
Also, valve spring pressures are rather low for the solid tappet valve train design in this engine. Therefore cam faces are not under high shear and surface friction as in other engine designs. As a result, oils with low ZDDP levels provide adequate lubrication of critical valve gear. The remainder of the engine is very robust and is lubricated using a two-pump design; one for the lube circuit, the other for the oil cooling circuit (remember, this is an air/oil cooled engine).
As a result, oils that tolerate high heat without viscosity breakdown are desirable. High levels of ZDDP are not required. These engines are 3-way CAT equipped so, high levels of ZDDP are undesirable as this additive can render the CAT inoperative.
The oilhead design also utilizes a separate gearbox that is lubed with GL-5 hypoid gear oil in its own reservoir. Finally, the clutch is an automotive design, again, much like the old VW 4-cylinder design and suffers only when the rear engine seal fails and wets the dry clutch, necessitating a change.
Given that the engine lube oil must lube only the internal engine parts, this simplifies the task of the engine oil considerably, leaving the owner with a number of choices for engine lube oil.
My BMW boxer, a 2001 vintage R1150GS has a factory recommendation as follows;
Engine oil grade: brand-name HD oil for four-stroke spark-ignition engines, API classes SE, SF, SG; combination with CC or CD specification.
The recommended OCI is 6000 miles for normal operation. Viscosity recommended is 15W-50 for temperatures here in the Houston, TX area.
Given these requirements, BMW boxer owners have a wide range of oils to choose from.
I have run Mobil 1 15W-50 EP auto oil in my boxer ever since the factory fill was changed. My engine uses no oil, routinely gives 42-43 MPG commuting and the engine stays clean and quiet.
With 35,000 miles, I have yet to begin UOAs. I use Mobil 1 due to availability, tolerance for heat as well as price.
