"Double-VANOS" is BMW-speak for variable valve timing. Car is a 2000 BMW 528i, it had a little bit of a hesitation from a standing start when using thicker oils (oils like 15W-40 fleet dino [used during an A-Rx rinse], and BMW's HP Syn 5W-30 during extended intervals, as it thickens up beyond a 30 wt.) When accelerating from rest with a constant throttle opening, the car felt as if you were pressing the gas, letting off the gas a bit, and then pressing again. Kinda subtle but definitely present. The slight hesitation just off idle is completely gone when using thinner oils like Chevron 10W-30 [used during an A-Rx wash cycle] and German Castrol 0W-30. I thought it might be a dirty throttle body, clogged fuel filter/injectors, or intake leak. Nope, it seems to be related to oil viscosity! Huge improvement after I dumped the 15W-40 and installed the GC 0W-30. In fact, with GC, the engine runs spectacularly: there is a nice high-rpm "kick" present, similar to a Honda VTEC engine. So far, this engine and GC seem to be an ideal match! I just hope the GC doesn't thicken up to a 40 wt. I found this regarding double-VANOS:
quote:I'm theorizing that an oil which is too thick will not flow quickly enough in the double-VANOS mechanism, and hence the slight hesitation. Things may be different in the "M" engines (and the earlier BMW engines), which are spec'd to use thicker oils, but with this engine, there is a noticeable performance decrease with thicker oils. I also find it interesting that for this series of engine, BMW explicitly approves of Mobil 1 5W-30, which as everyone knows is a thin 30 weight. Currently, most of the other Euro manufacturers call for an ACEA A3 oil, which would mean M1 0W-40 or 15W-50. Jason
At idle, the cam timing is retarded. Just off idle, the DME energizes a solenoid which allows oil pressure to move that cup gear to advance the cam 12.5 degrees at midrange, and then at about 5000 rpm, it allows it to come back to the original position. The greater advance causes better cylinder fill at mid rpms for better torque.