Quote:
Originally Posted by stephen wilson
I'm pretty sure all production engines bypass the filter on high pressure (when the oil is cold).
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Some do, some do not. While the concept of an oil filtration by-pass seems like a good idea, a lot depends upon how it is done and how, when, and how dependably the by-pass operates. Approaches have been all over the map, some OEM’s put the by-pass in the filter mount (Porsche), other use a by-pass valve in the disposable filter itself. Others use none at all. Each has its own merits and drawbacks.
In a modern engine running a multi-weight full synthetic oil, there is really no need for a cold engine start by-pass, the oil viscosity change provides that function itself. Some would suggest that even then the by-pass would be a good thing if the filter clogged with debris from failing engine components as it would still allow some oil to circulate; but unfortunately by the time that would happen in a Porsche, the engine would already be toast and need to come apart anyway due to the damage done to the bearing surfaces by the circulating abrasive debris. And if there were a by-pass in this situation, the circulation of the contaminated oil would only worsen the situation; so at least if the oil pressure drops off due to a clogged filter, you would get a warning light and could shut the engine down before things got even worse.
Most by-pass valves are simple spring-loaded devices, which sometimes get stuck in the open position either temporarily or permanently (and why some use the “in the filter” style so it is regularly replaced with a new one). Unfortunately, you get no warning when this the by-pass fails, and dirty oil goes back to the bearings, and things get ugly.
We have had a lot of customers running without the by-pass for a lot of miles and over a wide variety of temperature conditions; to date none has suffered problems that could be tied to the lack of the by-pass, and during those miles every drop of oil was filtered at all times.