I understand what the anit-drainback oil filters do, and I also understand that most oil filters come with anti-drainback valves. I've heard that the OEM filters and the Mann filters are properly equipt with anti-drainback valves, but I also know that Fram filters also contain an anti-drainback valve. I now because I changed my oil yersterday and saw the valve.

But why the fixation on this valve?

Here is why I ask.

On a Honda, or a Toyota, or a Mazda, or, as with most cars, the oil filter sits on the side of the block. When you shut off the engine, if your oil filter does not have an anti-drainback valve, most of the oil in the filter will drain back into the engine's sump, leaving only minor amounts in the oil filter. The next time you start your car, your engined has to fill up the oil filter before it ever starts pumping oil to the rest of your engine. A bad scene.

But with the 850, where the oil filter is mounted upside down, practically below the engine's sump, why is it necessary to have an anti-drainback valve?

If the oil filter was mounted horizontally, or even right-side up (with the screw-on at the bottom of the filter), then I could understand. But with the filter being mounted upside down, what is the use of an anti-drainback valve?

Siphon effect?

Someone tell me why this is an issue on an 850.