Originally Posted By: goodtimes
So when the holding capacity is reached, that means the pressure drop is higher. How else do they determine holding capacity? So maximizing use of a filter should reduce flow.
With a positive displacement oil pump, the flow is not reduced as the filter loads up ... rather the delta-p increases while the flow stays the same. As the filter loads up, the delta-p increases until the bypass valve opens up. Even then, the flow rate should still be the same as long as the pump isn't in pressure relief mode.
What becomes 'dangerous' when running a filter super long on a dirty engine is that it gets closer and closer to running near the bypass valve setting, and therefore bypass events can occur way more often (especially in cold temperatures), which isn't really desirable.
And as you mentioned earlier, I believe the 'holding capacity' is defined when a certain delta-p is achieve ... probably somewhere close to the bypass valve setting.
Originally Posted By: goodtimes
Filters vary greatly in size, how can a thimble size hold the same as the garbage can size? They say one amount of grams, say 32g. They also say 15k or whatever, on what car, a new one or the oldest, most worn out one that exists? A person would have to cut open their filters and try to assess what is the best plan.
Yes, this is a somewhat nebulous area and hard to nail down. Typically the holding capacity will be linked to a specific filter model number - so that's pretty easy to get.
Not sure about how they come up with the mileage rating. The statement format used is typically ... "provides up to 15,000 miles of engine protection." Key words are "up to". I would assume the mileage claim would hold true on most engines in pretty good condition that have had good regular oil and filter changes.