Originally Posted By: BAD1
I have a question how or why do they have a mileage restriction on some filter well really all I guess, how do you know when the oil filter is done it's job, finished and ready to be changed because it usefulness is over????
I would assume the manufactures use some kind of "average" contamination rate of the filter due to a "normal" car, and then determine how many miles that equates to in a "normal" car.
Originally Posted By: BAD1
What happens when you push a oil filter past it's limit??
As the filter gets more and more contamination in the media, the pressure drop across the media will also increase more and more. When the pressure drop becomes equal to the setting of the bypass valve, the valve will start to open so the pressure drop doesn't exceed a certain limit.
Of course, if the bypass valve doesn't work correctly and/or the media is weak in spots, the media can start to tear and fail.
The main purpose of the bypass valve is to ensure the engine still gets oil (its unfiltered though) and the media doesn't fail from high pressure difference across it.