The Subaru bypass pressure thread got me thinking.....I've read that some people don't recommend Mobil-1 and K&N Filters due to the low pressure of the Pressure Relief Valve, basically saying that the oil pressure, even at idle, was higher than the rated pressure for the filter, therefore, oil is not being filtered, but bypassing the element. Owning a 1.8T Passat, you tend to get a little paranoid. I checked into some filter specs for bypass relief valve pressure: Mann: 36 psi Purolator: 20-25psi K&N: 8-11 psi I decided to e-mail someone at K&N to see what they said: my e-mail: I have a 2004 VW Passat with the 1.8T engine. While trying to select the best filter for my application, I came across the tech specs (http://www.knfilters.com/search/product.aspx?Prod=HP-3001 ) for the oil specified filter, the HP-3001. Under the specifications the Relief Valve PSI is listed as 8-11. Could this be a misprint? Other filters, including the OEM version, have a Relief Valve PSI of around 30PSI. I’m worried if the listed pressure is accurate, that the relief valve is open all the time, as the minimum hot oil pressure for my engine at idle is 18.9. Anything you can do to clear this up would be greatly appreciated. Thanks, Mike His reply: The 8-11 psi setting is the correct specification for the HP-3001. This is a differential pressure rated at a 1/10 gpm flow rate. I do not know what flow rates our competitors use for their published relief pressure specification, however I know that VW typically rates their pressure at slightly over 1/4 gpm flow and "around 30" psi would be close. However, the relief valve will not be open all the time as the consumer is concerned. The 18.9 engine psi at idle you mention is system pressure, typically monitored downstream of the filter. The filter relief valve setting pressure is differential pressure, that being the difference in pressure upstream versus downstream of the filter. The relief valve is designed to open when the oil is cold (high viscosity) or if the filter media becomes clogged due to extreme contaminant build-up. This is so that an adequate amount of oil can bypass the filter and reach the engine bearings and other critical areas. Example: With a clean filter and the engine warmed up the upstream filter pressure might be 19.9 psi at idle. The downstream pressure is 18.9 psi, which the customer reads on the oil pressure gauge, therefore the differential pressure is only 1 psi. At highway speeds the upstream filter pressure might be 45 psi, and the oil pressure gauge may show 43 PSI downstream for a differential pressure of only 2 psi. The bypass valve would not be open under normal operating conditions unless the differential pressure reached the range of 8 to 11 psi for the reasons stated previously. I hope this clears up your concern, this is not an uncommon question or concern. This makes me feel a little better. Does this sound good to you guys?