Full-flow oil filters have been around so long that I doubt many in the trade remember anything else. Did you know that in 1955, the first of the legendary small-block Chevrolets didn't have built-in oil filtration? That oversight was quickly...
Full-flow oil filters have been around so long that I doubt many in the trade remember anything else. Did you know that in 1955, the first of the legendary small-block Chevrolets didn’t have built-in oil filtration? That oversight was quickly corrected the following year when the engine grew from 265 to 283 cubic inches, but it’s curious that the filter was omitted in a high-wear, low oil quality era of the 1950s. In those days oil filtration was a hot topic when “bench racing” and the argument broke down into two opposing opinions: full-flow and bypass filtration. Full-flow, originally with canister and later with spin-on filters emerged as the standard, mainly because it filtered every drop of oil circulated in the system. Bypass filtration tapped pressure from a convenient gallery, filtered it and dumped the clean oil into the oil pan. Only a small percentage of the oil was filtered in any one circuit around the engine, so it’s a little like emptying an aquarium with a dip net … you get it all eventually, but it takes a few scoops.
Full-flow is better, right? I’m not so sure. Clog a full-flow filter and get into the bypass valve and the result is no filtration at all. Varnish and/or sludge the valve shut and it’s even possible to balloon or rupture the filter can, especially with cheap white-box parts. Bypass filtration, because it doesn’t act as a restriction in the oil system, can use more, finer filter media, allowing not only better filtration, but longer filter life. And with today’s long-life high tech engine oils, the additive packages last longer. Particulates, however, are hard to suspend and disperse in higher loadings as the drain interval gets longer and longer. Better full-flow products are the current answer, but I can’t help feeling that a big bypass cartridge filter would do the job better, longer. If it clogs, no bypass valve is needed, as the system simply taps less pressure from its supply gallery. You could even measure this back-pressure and sense remaining filter life with accuracy.
Bypass filter kits were once popular aftermarket accessories and some were still around when I first picked up a wrench in the 70s. The problem with the aftermarket solution was and I suppose still is that you need to tap a gallery, find a place to mount the unit and then rig up the drain. The source could be as easy as “teeing” the oil pressure sender fitting, but getting the oil back into the pan is another matter. Drilling the oil pan is dangerous business, and who wants to pull it to weld or braze in a fitting just for an oil filter? And these days there isn’t much under hood room to mount the unit anyway, unlike my 1974 Slant Six Valiant. The kit I really wanted used, believe it or not, a roll of toilet paper as the filter medium. It was supposedly cheap and effective, but there was an issue bigger than hacking the engine’s oil system: putting up with the jokes from my buddies.