Re: Zddp question

Posted by su8overdrive On 2022/9/30 20:13:39

Re: by-pass vs. full flow oil filters, addreessed that on these forums a couple years ago:

Most Packards, if they have an oil filter, have a bypass, other than 1934-39 senior eights and 1935-39 Twelve, a rarity shared with the 1933-on Pierce-Arrows, which introduced hydraulic valve lifters, and 1931-33 Auburn Twelve, the latter surely the best buy in automotive history. So the below may be of interest.

Expanding on the above discussion of bypass vs. full flow filtration, here's an interesting letter in the 2006, No.5 Auburn-Cord-Duesenberg Newsletter by Al Light, Williamsport, PA, which is, coincidentally, where Lycoming, builder of all A-C-D engines, is still based:

"I really enjoyed the editor's comments on the club website about the real value of having an oil filter.

In the early 1950s while at Ford Engineering I was fortunate to hear an argument of "Full Flow" vs. "Partial Flow" oil filtration. The pro "Full Flow" people seemed to be more interested in the positive sales pitch that this system provided while the "Partial Flow" people seemed to
have a more solid engineering approach. The chief engineer from Fram Corporation stated the big difference was the allowable filter pressure drop. The larger the pressure drop, the finer and more material will be caught. With the full flow system you are restricted to approximately 10 pounds per inch drop across the element, and also require a bypass valve that will open when this pressure drop is exceeded. This of course is to protect the engine from oil starvation in the event of a plugged filter. With the partial flow, or sometimes called bypass system, the pressure drop is full engine oil pressure since
the oil discharges from the filter directly into the oil pan and not under any pressure. The system is automatically
bypassed if the filter plugs. It was also noted that a denser filter element is used on the partial flow system.

The Fram engineer summed up his thought by stating the answer to the argument was obtained by considering the following question: "Is it better to filter all of the dirt from part of the oil or to filter part of the dirt from all of the oil?"

He also stated that with the full flow system the bypass valve may open under cold starts and sometimes opens at high engine RPM when the allowable pressure drop may be exceeded. This results in no filtration under these conditions. His other comment was that the biggest advantage to full flow was to catch the machining chips, etc. in new engines. Fram's final approach was to propose the use of a combination system that did both full and partial filtering. I'm sure that this would have increased their filter business. I am not aware of any such system ever being used."


I can only add my auld aircraft/auto mechanic/machinist/pilot, blown '37 Cord, Auburn 12, Marmon 16-owning friend said they were taught in tech school that a bypass filter will eventually filter all your engine's oil after a drive of 50 or so miles.

Another friend with '59 and '63 Ferraris showed me they left Modena with both full and bypass filters, as do some more recent trucks and heavy equipment, some of the latter coming only with bypass filtration.
Such equipment is likely to run hour after hour, shift after shift, so all the oil would easily be filtered.

As we've observed, for all the technological breakthroughs since Packard folded, much engineering is cost engineering,
but don't know if this is the case regarding bypass vs. full flow oil filtration.