Originally Posted by dguru

You would have had to drill and thread a fitting on the filter housing because an engine designer would never provide an access plug to the unfiltered side of the filter in order to insure that the average shade tree would not connect anything to the unfiltered side. I bet if you removed the filter housing you would see this. However this is all moot because again the deposits that the spinner filter gets would go through the main filter anyway. Also the spinner filter does not have much room for trash as it would reduce efficiency as it builds up. It also hard to clean and thats why most truck makers opt for a throw away spinner filter.

Again the point of a bypass filter is NOT to make the main filter last longer! The reason you use a bypass filter is to "finish" the oil. In other words clean it to a finer level so that these small deposits don't continue to circulate through your bearings. Thus reducing the need for frequent oil changes. It makes your oil last longer. It has nothing to do with the main filter service.

Now one might say well why don't they use a finer main filter. The answer the finer you filter the more you restrict the oil flow and the larger the filter you would need to compensate for that restriction at that flow rate. Thats why the bypass method is used. It filters a small amount of oil to the micron level on order to extend oil life.

There is one drawback to adding a bypass filter to an engine that was not designed for one. It takes some oil away from lubing the engine. Most engine designers install a higher output pump when the specs call for a bypass filter. Now that does not mean adding a bypass filter is going to create a problem but when you add twin turbos or anything else along with it you may or may not run into a problem. Just something to think about.