During my reading on the internet and especially during sometimes heated discussions about oil starvation on the M96/97 engine family, I heard references to a “bypass” on the stock Porsche oil filter. One inference I came away with was that this was a bad thing with respect to the design of the oiling system. The “fix” was to go with a spin on oil filter modification. I don’t want to wade into that argument except to say that I think it is flawed thinking. More on that below. Regardless, when I was rebuilding my M97 engine, I thought that with all the new parts I was using, I should replace the plastic canister that the oil filter is housed in. I was in a little bit of a hurry and decided to buy the canister at my local Porsche dealership, Porsche Cary. It turns out that Porsche sells the cansister and the filter as a unit,. I guess I’ll never know if they thought the canister had a life limit or whether they were just adding yet another small profit center. The price was not too outrageous and I went for the combo. This left me with an old canister. Months have gone by but the other day I cut the canister open to see what was what. At the bottom of the canister I found a round plastic disc with a metal “button” in the middle. The plastic disc was floating on a collar with obvious openings where fluid could enter/exit. Intrigued, I pried the plastic disc with a screwdriver and it popped right off. What did we have here? The following pictures will be worth many words but underneath the metal button there was a spring. When I pressed on the plastic disc, the metal button popped up. It was basically a spring loaded check valve. If you refer to my Porsche M97 Oiling article, video Part 2, around 4:55 it discusses that oil enters the outside of the filter element and exits up through the middle. So I can see that the bottom of the metal disc, if popped open, would allow a bypass of oil from the outside to the middle. This is certainly the basis of the “bypass” comments.
I did a test of the metal disc. I mounted it on my kitchen scale and measured the force required to open the disc. Around 9 pounds force. I then measured the diameter of the disc underside that would be exposed to oil pressure. I conservatively measured 0.65 inches. Calculating force over area, I obtained an openinng pressure of 27 psi or about 1.8 bar.
So what to make of this? To my thinking, the only way that the relief valve in the bottom of the filter housing would see a differential pressure of 27 psi is if there was a pretty major degredation or clog of the filter element. Google AI says filters typically have a 5 to 15 psi drop, which seems a little high to me. RSMike on Bobs The Oil Guy forum says this (which makes more sense to me): I’ve conducted some testing on my car to see the different pressure drops across different filters. The results? – It was a fizz. When the filters are NEW, they all represent zero restriction to oil flow and pressure. The *actual* loss shown on the graphs will be because of the change of oil flow direction, not the media itself.
So my conclusion is that the relief valve in the bottom of the Porsche OEM filter cansister is there for your engine’s protection, in the event of something very bad going on with your oil filter. It is most certainly not robbing you of critical oil pressure in high G corners! And I would consider buying a new canister every once in a while. It is virtually impossible to test the check valve “in-situ” so it might be a good idea to get new parts in there occasionally. Yeah, I know you are going to hate what Porsche is charging you for an oil filter and canister but considering the fact that we are now routinely ponying up $20/quart for boutique oils to protect our engines from bore scoring, I think the filter/canister purchase is a good idea, while you’re in there.
New Hill Garage 
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