I've been doing oil changes on my own vehicles for 30 years now, and just experienced something that disturbed me a little. I've been using Wix filters now for 15 or 20 years, and as far as I know, they're great filters. On my Tahoe, I noticed that the oil pressure dropped earlier this spring. After I did an oil change I noticed a lot of sludge in the oil after switching to Valvoline synthetic. After changing the oil/filter, the oil pressure returned to normal. A couple of months later, before the next oil change was due, I noticed the oil pressure dropping again. I changed the oil filter again, and the oil pressure returned to normal, once again. Only this time, I didn't have access to a Wix, so I had to use another brand. This time I wasn't losing any oil pressure, or very little, even when it was time to change my oil again this month. When I removed the drain plug, the oil wouldn't even come out right away, and came out in globs! It was all sludged up, but I wasn't losing oil pressure. I figure that the Wix does not have a bypass valve, so when the filter gets plugged up with sludged oil, the pressure drops giving you warning that something needs attention ASAP. This other brand of filter had a bypass valve and allowed the sludge to pass straight through, all over my valve train and everything. ------------- I had never thought of the cons to having a bypass valve until today. I will now always keep a stock of a few Wix filters (or ACDelco, or other decent brand that does not have a bypass filter). If I see the pressure dropping, I know to change the oil pronto, even if the usual oil change interval has not yet passed.