There's an unfortunate confusion built into the nomenclature. Your primary filter will be bypassed by a pressure actuated valve if it becomes clogged, allowing unfiltered oil to circulate.

But this is not to be confused with the bypass section of your filter, which is a separate system. The bypass section is constantly in use, providing "slow deep" filtration of a small portion of the oil flow, which is then returned to the pan. The top 2/3 of your oil filter is the bypass section. The idea is that the primary filter can pass large volumes of oil to keep the system pressurized, but can't be very efficient, otherwise it would clog. But the bypass section doesn't have to feed the demands of the engine, so it can have very efficient media and will scrub the oil more slowly and thoroughly. In time, all the oil circulates through the bypass section.

Thanks, that helps clear up the confusion - checked a few videos on the spin on type which seem pretty straightforward as the bypass does just that, bypass the filter element to keep the bearings from seizing.

In essence the lower part of folded fabric is for higher viscosity (cold) oil to pass through similar to bypass mentioned in below link, as the oil thins it can then enter the spun cotton portion?

The difference being no physical valve.

https://www.youtube.com/watch?v=ecpkvsnKKNg

No. If the oil is too viscous to pass through the pleated filter, a bypass valve in the filter housing (not the filter element) routes oil directly to the oil galleries. Otherwise, all oil enroute to the galleries passes through the pleated element. Oil passing through the bypass portion of the filter is returned to the oil pan, rather than being routed directly to the oil galleries.

There is a physical bypass valve. It's located in the filter housing, rather than being incorporated into the filter itself, as is the case with many spin-on filters.

As infrequently as filters are changed, once or twice per year, I stick with OE from the dealer. Too much shady cost-cutting with the non Genuine filters. With all the globalization, mergers, subcontracting, etc. one brand/model filter that was good last year might be crap this year. Same looks same packaging but comes from a different factory. I would not rely on that media comparison thread from 2006 to be accurate in 2019. You can't go wrong with OE, and given the importance of the oil filter's role, I don't mind paying the five dollar premium or whatever to buy a Genuine part.

The floor sweepings media works good - (benz have millions of miles on them to prove that). And to be honest its a very "green" filter (our cars are very eco freindly :D)

As long as I owned my diesel W124, it got MANN filters or hastings (if found cheaper on ebay - like bent boxes etc) - they worked super. I did encounter one filter which literally was shedding the floor sweep media so I binned it.

That's nice. Your '98 E300 filter doesn't have the separate bypass section.

Thanks. My comment was not vehicle specific.

Here's a good video of some generic filters cut open
 

Are you sure this is how it works for the 605/6 type filters, seems a little complicated ? - what's to stop oil passing through both the pleated element and hidden cotton balls, the tube runs right through the middle on these filters with no obvious mechanism to divert.

Does the oil not just pass up through the middle exiting folded element part when cold, moving up to the use entire filter when hot - if filter gets blocked then valve bypasses the filter draining back down to pan.

The cartridge filters differ with oil pump to the inside out as opposed to outside in fir spin-on.

- just watched that last video, no way I am buying a Fram filter !!:eek:

I always liked the look of the Ferrari v12s with two Fram filters up top in front....so I like to buy Frams and channel Ferrari.

Besides I like Orange.

My comments were applicable to engines which utilize a two-stage oil filter, like the ones that you posted pictures of in post #1.

Perhaps you need to decide if you are inquiring about specific oil filters or specific engines.

Really?