I am highly skeptical of a claim that Frantz removes "everything above 0.5 microns." I hope nobody here is taking that as gospel. Most importantly, the source of the quote is not what I would call reliable. Some "guy" on a post who "claims" some VW mag in the '60s did it. So far, I have not seen ANY credible sources or testing on Frantz efficiency that give us much of an indication of their actual performance.... good or bad.
I not against TP filters or bypass at all, but the Frantz thing seems to be based more on some widespread "belief" that it's great versus anything concrete. I admit to being bothered by that, which is why I chime in most times when the subject comes up. I promise that I will shut up or join the chorus if someone can produce credible (by a reasonably objective, scientific standard) test results.
FYI, I am using bypass on two of my trucks, Racor ABS 3 um absolute units that are very similar in operation to the Frantz. The difference is that the paper is engineered for filtration purposes and rolled in such a way to create a specific flow, efficiency and capacity. In other words, you know that what you install in there will deliver a specific effect.
With a TP filter, you might get great performance from one roll and lousy from another but you really don't know exactly what you are getting either way because you can't rate the efficiency of a roll of toilet paper before you stuff it into the canister.
Going back to that supposed test in the VW magazine, if that's a real deal you would want to know specifically what brand and type of paper they used because that would be key. As widespread as the Frantz has been for so long, it seems incomprehensible to me that there isn't just a ton of test data and a lot of specific advice on which paper produces the best efficiency.
I will agree with the point that someone will likely make that any bypass is better than none. Thing is, for all anyone knows, the efficiency is no better than the FF filter that's already in there and maybe worse than some of the top dollar premium full-flows you can buy.
As to bypass filtration itself, I look at it as an oil life extender, not so much an engine life extender. The reduction of engine wear via filtration is on a curve, a curve that gets very shallow below a certain threshold of oil cleanliness. The flattening of the curve seems to start at absolute filtration near 35um. We have no real world tests (that I know of) that really show the difference in wear at points in that flat part of the curve. By "real world" I do not include those accelerated tests where engines are run on a dyno and fed large amounts (pounds) of contaminants and they measure how fast the engine wears out with different levels of filtration. Those test only serve to show how high a contamination level the engine can withstand.
In the real world of light duty stuff, what you and I drive mostly, contamination inputs are very low. A lightly stressed gas engine produces about 2 ppm of iron per 1000 miles. So in 10K miles, it has gained 20 ppm of iron. That's 20 PARTS PER MILLION, essentially nothing and well below any engine manufacturer's caution thresholds, some of which run as high as 150 ppm or greater. The contamination levels of a lightly stressed engine with few external contamination inputs (these inputs come mostly from faulty air filtration or crankcase sealing), the need for bypass is greatly reduced if not eliminated because the contamination levels of the oil never reach a dangerous level and the difference in wear between "clean oil" and "really clean oil" is not much. As a result, looking at it strictly from a financial POV, bypass doesn't pay for itself from the engine wear perspective in the short run or for easily run engines in clean environments. They pay off best with engine are are worked hard, long, long OCIs and/or with a high rate external contamination (e.g.HD engines, worked hard in dirty environments with spotty maintenance).
The Frantz and other similar setups were viable for everyday owners back in the era when oil wasn't so great, air filters were only 85 percent efficient, full flow oil filters (if they even had a filter or a full flow filter) were doing good to break the 50um absolute barrier, and engines shed metal like mad from flat tappets, Morse chains, marginal metallurgy and so-so machining (versus todays's standards on those things). All that contributed to very much higher levels of wear metal in the oils and the 3K OCI was as much based on these contamination levels as it was the actual condition of the oil. You could see a substantial benefit with a Frantz in those days (even if the absolute efficiency was only 35 um or so) because the contamination inputs were so high. Most of todays engines produce only a fraction of that contamination. There are a few exceptions yet, and the old timers are still on the road, but you can see the differences in contamination if you start comparing modern engine UOA with old ones. Moderr oils can really help an old engine wear better but even given the same oil, an older engine will shed more metal than a modern one.
Bypass is a great oil life extender, so if you plan to run long OCIs, 15K and up, the bypass can make itself financially viable from that angle if you plan to keep your vehicle long term.
I am nearing the end of a 2+ year, 15K OCI on conventional 10W30 on my truck for which a bypass system has been installed for 10K of those miles. I tested the oil at 10K and it was in great shape... though that is no feat in itself really because you will see it's done quite regularly and successfully without bypass if you peruse the UOA section.
