http://www.nascar.com/2005/auto/09/12/filters.npn/index.html Many of us older mechanics or technicians remember oil bath air filters and canister type oil filters where in a pinch, a roll of toilet paper would do. Those filters worked well, they were easy to maintain, cost little to buy and replace, simple to service. Today's cars and trucks have filters by the bunches: Oil filters, air filters, fuel filters, cabin filters, canister filters, coolant filters, transmission filters and in-tank sock filters. All of these filters have one job, to trap solids and prevent their circulation. Top-quality oil filters will trap and filter out particles of dirt, trash and metal that is 10 to 14 microns in size. Other, lower quality, oil filters may only be capable of filtering trash smaller than 40 microns. The element of the filter is very important, but so is the way it is constructed and the materials used to build it. Last, the testing it receives before being placed on the auto parts shelf should create a comfort zone for those wanting to keep their car forever. So buy top quality filers, like Wix, to insure trash, created by a gas consuming engine, isn't going to cause excessive engine wear. There is always a pump that sends the respective fluid to the filter first. The idea is to filter the fluid before it is pumped to the critical rubbing or revolving components. But in certain instances, commonly on a very cold morning, the filter is filled with oil that is almost a gel. When this occurs, the pressure to the filter is much greater than the oil pressure exiting the filter because the pumped oil is trying to push this very thick, very cold oil out of the filter. When this occurs, the bypass valve will open (if the pressure differential is 15-25 psi depending on import versus domestic) and allow unfiltered oil to be circulated until the oil is warmed up enough to move the cold thick oil from inside the oil filter. This is exactly why you should always allow your 1986 or newer car to idle for 30 to 60 seconds before placing it in gear and driving it away. That short time frame is when unfiltered oil is being circulated and damage may occur if the engine is loaded and accelerated. It is far better to just let the engine idle, unloaded until the oil filter begins to filter the incoming oil. Other than my Dad and a few of his old-time buddies, no one in the auto industry that is "oil smart" suggests you change the filter every other oil change or change the oil and not the filter. Always change your oil and filter at the same time. ASE-Master Technician and NASCAR Performance's Consumer Crew Chief, Mark Salem, owns Salem Boys Auto in Phoenix, a Member of the NASCAR Performance Network. For more Car Care Tips or to find a technician you're going to love -- just go to NASCAR.COM and click on Auto Service.