Do you beleive this MOBIL1 FAQ? Seems off base to me. 06/17/2002 Bypass Oil Filtering I read through the archive but could find nothing on "bypass oil filtering." I'd like to add the Oilguard System to my 1995 Ford F-150 with 50,000 miles. The literature and reports of performance of this type of system are quite positive. I've been using Mobil 1 in all my vehicles for 20 years and plan to continue that use. Has Mobil done any tests or does it have any recommendation regarding bypass filtering? -- Paul Edstrom, Stanchfield The average conventional spin-on filter for an automobile typically has a 40-50 micron absolute rating. That means particles larger than this size will be caught by the filter element. The Mobil 1 oil filter has a 15 micron absolute rating. Some bypass systems are rated at 1-3 microns absolute. We have not done any performance testing with the bypass oil filtering system you have suggested. Although a good filter is vital to the health of an engine, bypass oil filtering systems are capable of extremely fine filtration. It is usually not necessary to filter an engine oil down to cleanliness levels below the 10-15 micron range. We do not recommend filtering an engine oil down to below 1 micron particle size. Below this size, a filter may begin to capture vital components of the additive package.