Originally Posted By: E150GT
I do in the Mazda since I can. I don't in the truck since it would make a mess. Some say not to do it since it's allowing unfiltered oil to go through the engine but I don't think it's any different than dumping your oil through the valve cover.
I always thought the same thing. Worrying about "unfiltered" oil from a clean bottle of oil being poured into the filter, maybe 50-100cc max, when you are pouring 4+ qts into the fill tube.
On vertical filters with the opening up, I do prefill them, if horiaontal, I fill them, let the media absorb the oil, and do it a few times so their is no free oil in the center tube but the media is saturated. No idea if it really helps anything or not, but it makes me feel good.