Originally Posted By: QuadDriver
Originally Posted By: 440Magnum
Ummm... No. To everything you wrote. Use the search function and find where people here have MEASURED the across-filter pressure drop (PSID- PSI differential) and compared it to the bypass valve setting. Filter bypass valves almost *never* open, unless you use 20w50 conventional oil, have a high-volume oil pump and loose or full-groove racing type bearings, and then rev it to redline first thing on a sub-freezing morning.
What you are describing actually does happen on WWII vintage aircraft, where at times the oil in the oil *coolers* can get so cold it won't flow (they call it "coring the coolers") and the oil inside the engine gets too hot as a result... but those things use straight 50-weight oil (or heavier) and operate up where the air is well below 0.
no, what I am describing is what occurs to any motor that does not use a sock filter or an exceedingly large spin on accompanied by a differnt type of filer mount appliance.
do not confuse the oil pump bypass, with the oil filter boss bypass, or even the oil filter bypass - some applications have all 3.
fwiw, the oil filter bypass in the SBC opens at 10psi.
you need to consider the volume of oil pumped PER MINUTE.
you hear the old phrase 'xxxx takes the path of less resistance', well oil, like electricity takes ALL paths. some more than others. with the actual amount flowing due to the oil filter bypass and the total volume actually pumped per minute, all oil essential hits the filter each minute, just not in the manner in which most people think it does.
google up 'grumpysperformance', its a website with hundreds of drawings, charts, millions of links and dispells all the myths I encounter here regarding where oil goes in an engine and what it does. Of get a few hipo rebuilding books for the manufacturer of your choice.
But please dont think the wussy little spin-on on your engine has all the oil pass thru it.
I understand the difference between pressure relief valves, built-in-the-filter bypass valves, and the internal bypass valves in the filter perfectly well. I'm talking about ANY valve that bypasses the oil *filter* and sends unfiltered oil from the oil pump to the engine... NOT about the pressure regulator valve that opens when the oil pressure hits 40 (or 70, or 80, or whatever) PSI and dumps the extra oil the pump is moving but isn't needed to maintain oil pressure BACK to the engine.
Please don't think the "wussy" little spin-on is ever in bypass under normal circumstances. It may have a bypass valve that opens at 10 PSI, but even a smallblock chevy running at 4000 RPM and 40 PSI of oil pressure probably only has a 1-2 PSID *across* the oil filter media. My two 440s with their high volume oil pumps and running 70 PSI of indicated oil pressure also have a 1-3 PSID drop across the media of the PL30001 filters I use.
The bypass valve should almost *never* open. Even with "small" oil filters, if they are properly sized to the engine. I'm sure the teacup sized stock filter on my wife's PT Cruiser is perfectly adequate to pass the full oil flow required by the non-turbo 2.4 with less than a 5 PSID drop.
Again, I refer you to tests documented on *this* site which indicate that filters installed in engines have very *small* PSI Differential across the filter. Tests you find on the web where they pump oil through a filter and then into an open pan (no restrictions such as bearings, lifters, etc. DOWNSTREAM of the filter) are completely UNrepresentative of what happens in an engine. In a real engine, the total pressure inside the filter is high, but the restriction that generates the back-pressure is caused BY THE CLEARANCES IN THE ENGINE, and NOT by the filter. The engine's oil flow restrictions downstream of the filter keep the total flow volume well below what the filter can handle without bypassing any oil.
