When running the centrifugal filter is spinning at anything up to 15000 rpm. The oil pressure typically goes something like this: cold start = 3 bar, hot 1.5 - 3.0 bar, pressure relief valve opens at 4.0 bar. When I change my oil I find that two 4 litre cans take it up to a fraction over the top notch on the dipstick, so once it's filled the filter cannisters and gone round all the galleries I'm usually bang on the top notch. I tend to change all the filters when I change the oil, at 6,000 mile intervals, but I believe the official service schedule says you can leave it for 12,000 miles. I change everything because it comes in the service kit and there doesn't seem any point putting clean oil through dirty filters.